Internalization theory best explains CEMEX’s FDI Essay

1.Which theoretical explanation (or explanations) of FDI best explains CEMEX’s FDI? 1.Internalization theory best explains CEMEX’s FDI because CEMEX entered into many countries and bought domestic cement businesses instead of licensing. CEMEX has a great system and needs to protect it from competitors. 2.What value does CEMEX bring to a host economy? Can you see any potential drawbacks of inward investment by CEMEX in an economy? 1.The value is that CEMEX has a â€Å"Midas touch† that transforms a cement business into a thriving business. This brings great stimulation to the host economy and also helps in the construction field, which in turn helps to build cities and civilization. No, CEMEX would do well to invest inwardly, yet, CEMEX is better at acquisitioning businesses. 3.CEMEX has a strong preference for acquisitions over greenfield ventures as an entry mode. Why? 1.Acquisitions are solid because the business in the host economy already knows the demographics and the market. CEMEX just has to make the business better with little research. A greenfield venture would prove risky and not cost effective. 4.Why do you think CEMEX decided to exit Indonesia after failing to gain majority control of Semen Gresik? Why is majority control so important to CEMEX? 1.A licensing is very dangerous. CEMEX only have a 25% push with Semen Gresik. It did not have full control and the methods of CEMEX would be exposed and vulnerable to be stolen. CEMEX has a great system and does not want anyone interfering. 5.Why do you think politicians in Indonesia tried to block CEMEX’s attempt to gain majority control over Semen Gresik? Do you think Indonesia’s best interests were served by limiting CEMEX’s FDI in the country? 1.Indonesian politicians did not like the possibility of CEMEX taking over the cement market. Their interests were in domestic businesses and protecting the â€Å"purity† of their economy. No, Indonesia would have benefitted greatly if CEMEX was allowed an in. 6.What is CEMEX doing today? Do they still engage in FDI? 1.â€Å"MONTERREY, MEXICO- OCTOBER 8, 2010 – CEMEX (NYSE: CX), announced today that pursuant to the exercise of a put option by Ready Mix USA it will acquire its partner’s interests in the two joint ventures between CEMEX and Ready Mix USA which hav

King Hammurabis Code of Law essays

King Hammurabi's Code of Law essays King Hammurabi envisioned his code of laws to govern the people of Babylonia. Hammurabi's code is said to be a reflection of ancient society. He cared about making a name for himself; he wanted his laws to be carried down through generations and his reign to be talked about long after he was gone. Hammurabi started a civilization based on social structure and economics. In order to build a successful empire, he wanted to have a society that had structure and social order. He knew that he had to have a unified law that everyone could abide by and needed social structure so that he could create equality among the people. He wanted all of his citizens to live under the same set of laws so that they could work towards a common goal and have the same rights as one another. Hammurabi was the first to organize the world's first written set of laws that characterized political and military structures, social structure based on economic power, and social welfare. It was important to him to have the citizens trust the laws and one another so there was no chaos amongst them. However, he did organize the citizens into classes that were impossible for them to get out of and I feel this was ultimately ineffective at accomplishing his Hammurabi's code fulfilled most of the needs of his citizens. He gave them what they needed at that time to prosper: structure. In order to have a great nation you first must start with the people. They are the building blocks of a great nation. But in order to get the maximum productivity out of them, you need to set some ground rules. I feel the code was harsh with some of the punishments, but it was exactly what they needed at that time. These laws set up the structure and framework by which the king or government operated, became a tool for them to interact with each other, and created a justice system to help the people if they were wronged by another person....

Questions on Law Assignment Example | Topics and Well Written Essays - 1250 words

Questions on Law - Assignment Example The police officer who witnessed their act together with his back up team issued citation for the suspects. The gang moved a motion for dismissal of their cases on the ground that their citations were issued by officers who lacked probable cause. Legal principle: Prosecution’s reasoning The case is based on the principle of probable cause for making an arrest. Under the principle, a police officer can make a warrantless arrest, and citation, if there is a sufficient probable cause. A police officer can justify the move under probable cause in two circumstances. The officer must be able to explain the information that led to the assumption that the suspect was involved in a criminal act and the officer’s move must have been based on the suspected cause (Bergman and Berman, 2011). The likely ruling In the cases of Maryland vs. Pringe, Ybarra v Illinois and the case of State v. Sokolow, it was held that the presence of an incriminating evidence and reasonable suspicion for m ground for sufficient probable cause to arrest a suspect. It was further held, in the case of Alabama v. White, existence of probable cause is sufficient. The judge is therefore likely to uphold the case due to sufficiency of probable cause that the officers had (Bergman and Berman, 2011), (Carmen, 2009), (Meeker, 2004).... The gang can use this principal to suppress the paper (Meeker, 2004). Prosecution’s likely argument The law exempts the need for warrant before a search in cases where the searches are immediately related to an arrest. In the case of Colorado v. Bertine, the courts held that searches of a person’s possession are admissible if the search is done within the immediate scope of the arrest. The prosecution can thus argue that the retrieval of the paper was incident to the issuing of citations and therefore admissible (Carmen, 2009). The judge’s likely decision The judge is likely to uphold the evidence. This is because the suspects were under the authority of the police and the case of Colorado v. Bertine would be more applicable (Carmen, 2009). Question 3 Search of Ma’s car Tony accepts citation and gets into Ma’s car. A police officer then asked to search Ma’s car and she sped off. Legal status of the search Ma was obliged to let the police offi cer search her car. Reason Search on motor vehicles are governed by the Fourth amendment. Under warrantless search and frisk, a motorist can be searched on two grounds. The motorist must have been reasonably suspected of association with a criminal act. A search is also called for if the police officer feels threatened. The basis of a motorist’s association with a criminal act was established in the case of Pennsylvania vs. Mimms in which it was held that there must be a legal ground for stopping the car (Carmen, 2009). Persuading the court that the search was invalid A search, considered as a breach of a person’s privacy, is valid if it is done legally. The general rule for warrantless searches is that they have to be done with free consent of the suspect

Islamic finance and conventional finance Research Paper

Islamic finance and conventional finance - Research Paper Example There is a growing global concern of the inequity in the allocation of wealth and income in the modern world, between and within countries, than has been witnessed before, with little hope of bridging the disparity. In this perspective, this essay will discuss ways in which Islamic finance can be seen as an innovative way that could substantively redefine finance and why it is different from conventional finance. Islamic finance is distinguished from conventional finance by the key attribute of adding moral and ethical aspects to fiscal transactions, hence providing a practical alternative to promoting responsibility in a free-market economy (Warner 301). Unlike the conventional financial and banking system, Islamic finance prohibits the opportunities for gambling-like speculation (or maysir), exchanging money for money (or riba) and making profit maximization the only endeavor for investment managers while disregarding other human perspectives of wealth. Instead, Islamic finance has innovatively introduced financial products based on Islamic law and also regulated and reciprocated by conventional monetary rules and regulations. Islamic Finance Products From the below examples, one can see that Islamic finance is geared towards reducing financial exploitation, especially among the less privileged. All rates of return are determined by the asset transaction, unlike conventional finance systems that base the returns on the interest accrued from loaned money (Warde 124). This is why it is increasingly appealing not only to non-Muslim countries, but also non-Muslim individuals, by redefining the way they perceive financial transactions. Istinaa: Also known as Commissioned Manufacture, Istinaa is a contract for the manufacture of goods under the perspective that speculation avoids the sale of a product that a person does not own yet. A promise under agreed specifications is arrived at, and a bank commissions the manufacture, hence undertaking the risk, and later sel ls to the buyer at agreed profit (Timur 799). Ijara: This is a leasing contract in which a party obtains an asset under lease for a specified cost and time from another, often a bank. All the risk is borne by the bank while a portion of the installments pay towards completion of the purchase at the time the asset will be transferred. Mudaraba: This is a trustee-type partnership financing whereby one party offers capital and another labor. Musharakha: This is equity participation whereby the involved parties contribute capital in terms of technical expertise or assets and set an agreed percentage of the risk and returns. If a bank is involved, it purchases property alongside the customers, and repayments are partly constituted of payback and rent. Differences between Islamic Finance and Conventional Finance In Islamic finance, there is the notion of a captive market, where products are based on Islamic principles and the market comprises of customers willing to adhere to the concepts of their religion. All transactions are based on the principle of sharing profit and loss, with returns varying depending on a bank’s performance. Customers can take part in profit sharing in more equitable ways than getting predetermined returns. On the other hand, in conventional finance and banking, customer returns are irrespective of a bank’s profitability or performance (Kadri 53). The banks only treat customers as depositors who do not receive any compensation apart from interest. Unlike conventional

Marketing-Defining a Communication Plan Essay Example | Topics and Well Written Essays - 500 words

Marketing-Defining a Communication Plan - Essay Example Graves Enterprises is doing well in its business activities in the market while it has been focusing attention on business expansion and develop a new customer base for their for their consumer products. However its business operations in particular require the company to adopt far reaching changes to the existing communication strategy and its orientation. Any communication strategy must have a customer retention focus that will ultimately produce the desired results. While this would effectively address the concerns raised by the consumer marketing director, there would be a greater degree of structural changes in communication within and without the organization (Zambardino, 2003). 47% of customers being retained would have a positive impact on revenue and profit related outcomes of the company. However $ 2 per unit in gross profit means nothing in the absence of the breakeven figures. The company may have lot of financial commitments by way of sales cost and therefore the net profit margin can be considerably reduce if the 47% customer retention plan fails. Thus the advertising campaign must be not only focused on the core customer base but also be extended to include the peripheral customer whose retention matters in the long term. As the Marketing Director commercial products suggests the current cash cows of the company would be compelled a carry a greater burden if the slow growth market tend to cash unexpectedly. The company might have a lot of problem children and dogs and as a result there might be a few cash cows and stars. Assuming the communication strategy as based on advertising works out successfully, the net return on the investment must be proportionately higher (Percy, 2008). In other words per unit advertising cost must be much less to support cash cows to move in to sustainable long term profitable stars. Thus the marketing communication plan of the company must be based on a proper alignment of the Boston Matrix with the

Nursing Decision Making Essay Example | Topics and Well Written Essays - 1750 words

Nursing Decision Making - Essay Example The advancement of technology has fueled various practices even in the nursing profession that has in turn caused a revolution in the way that nurses make decisions. Nursing embraces technology especially since there has been tremendous revamp as a consequence of its incorporation in the nursing profession (Hardy, Garbett, Titchen, Manley, 2002, p.200). There are conditions where nurses have to make sober and most feasible decisions when it comes to patients suffering acute conditions. These patients have to be accorded precise care in order to ensure their comfortable recovery in health institutions. Many patients have faced situations where they do not recover out of their illnesses since nurses do not have ample reasoning skills (Del Bueno, 2005, p.202). This is a result of nurses not making correct assessment of the patients they have in their centers, where they are supposed to evaluate the most ill patients and offer them the help they need. This papers purports to evaluate the importance of critical thinking for nurses in their provision of healthcare to patients. The situation in health facilities is that ‘at risk’ patients are fitted with a device that notices complex fatal situations such as cardiac arrests and warns the health administration in order to offer them quick response (Ebright, Urden, Patterson, Chalko, 2003, p.635). Quite often though, the nurses in all over the world do not possess the right planning skills when offering administration of health care to patients. While the degree of complexity in diseases is increasing indefinitely, nursing profession has adopted the information and technology empowerment to offer their patients the best kind of healthcare. However, this has not been totally comprehensive in offering healthcare and it calls for additional endeavors to coach nurses. The profession management found it fit to complement nurses with teaching in critical thinking skills in an effort to reduce poor clinical reason ing. Research conducted by an Australian institution for instance, showed that the level of ‘unsafe’ nurses in the United States stands at 70%. This translates to the high number of fatalities of patients under healthcare and in retaliation critical thinking education scheme has been boosted to allow for better service provision. Critical Reasoning It is defined as the clinical way that nurses and other healthcare providers perceive the situations that face them in providing their services to patients. It may also be called problem solving, critical thinking, clinical judgment or decision making. Clinical judgment is assessing the problem a patient is facing. Nurses therefore need to be well equipped to make a distinction between symptoms, collecting evidence of illness, understanding them, evaluating the possible solutions to ease illness and implement the best possible solution. The process of clinical reasoning is the ability of a nurse to assess the situation of the patients in terms of their symptoms, understand them, evaluate possible solutions, implement the best solution, know the outcomes possible for the patient and to internalize the processes (Thompson & Dowding, 2002, p.50). There is not really a certain way that nurses have to make sober clinical reasoning solutions. The basic process however involves ?collection, description and understanding’. The reason why nurses should learn from these situations is because precedence is also a form of clinical reasoning. When for instance, a nurse encounters a problem in a patient they are best placed to make a decision if they had encountered identical problems in other patients and therefore make decisions based on

Step by step design of a lock

Step by step design of a lock Introduction This paper outlines the step by step design of a lock in amplifier based micro-ohmmeter. This is very useful in measuring small resistances without applying large currents. And find its usefulness in tracing short circuits on printed boards containing sensitive components. The Audio Micro Ohm Meter uses synchronous detection to measure low value resistances. The circuit provides a variable frequency audio tone to indicate the resistance under test. Such a tone is invaluable when troubleshooting shorted tracks on multi-layer circuit boards because it is easier and quicker to observe 1. The source generates a 1KHz, 250mV peak square wave carrier signal that is injected into the unknown resistance, the resulting voltage across the resistor is amplified by the instrumentation amplifier. The phase reversing switch then rectifies the complementary square wave input, the rectified output is not all smooth so a low pass filter is needed. A Voltage controlled is then used to measure and indicate low value resistances such as track resistances on printed circuit boards. To provide a convenient indication, we want a ‘display that has high resolution (like a digital display) but is easy to read (like analogue meter) and that preferably doesnt even need to be looked at, so we can concentrate on the probes. To trace short circuits, the one thing we dont really need is high accuracy, since we are generally moving the probes 1. A muting detector then comes in to compare the control voltage with reference voltage. The Proteus ISIS software is used for the simulation of the circuit while a printed circuit board was used for the verification of the circuit. Resistor selection, analysis of waveforms , sensitivity and linearity of the device to supply voltage and possible improvements of the device were discussed. Excitation Oscillator One of the most useful ICs ever made is the 8-pin 555 timer and it is used in many projects. It can be used to build many circuits by just adding a few external components. NE555 is a popular version and it is suitable in most cases where a 555 timer is specified. Some low power types of the 555 are made, for instance the ICM7555, but can only be used when specified (to increase battery life) because their maximum output current of about 20mA (with a 9V supply) is too low for many standard 555 circuits. The ICM7555 has the same pin arrangement as a standard 555. The circuit symbol for a 555 is a box with the pins arranged to suit the circuit diagram: for example 555 pin 8 at the top for the +Vs supply, 555 pin 3 output on the right. Usually just the pin numbers are used and they are not labeled with their function. Standard 555 ICs create a significant glitch on the supply when their output changes state. This is not a problem in small circuits with no other ICs, but in a complex circuit a smoothing capacitor can be connected across the +Vs and 0V supply near the 555 . The 555 timer operates in different modes. The astable mode suits our design criteria. An astable circuit produces a square wave, this is a digital waveform with sharp transitions between low (0V) and high (+5Vs). It is possible that the durations of the low and high states may be different. The circuit is called an astable because it is not stable in any state: the output is continually changing between low and high. Our circuit needs a square waveform output of 4KHz, for this to be obtained an appropriate resistor value can be estimated by calculation to obtain the needed signal to drive the circuit Duty cycle The duty cycle of an astable circuit is the proportion of the complete cycle for which the output is high (the mark time). It is usually given as a percentage. The duty cycle of our circuit can be determined using Time period. The timeperiod (T) of the square wave is the time for one complete cycle, but it is usually better to consider frequency (f) which is the number of cycles per second 2. The time period can be split into two parts: T = Tm + Ts 5 Mark time (output high): Tm = 0.7 Ãâ€" (R1 + R2) Ãâ€" C1 Space time (output low): Ts = 0.7 Ãâ€" R2 Ãâ€" C1 we can determine our R2 using C3= 10nF, R1=1k and f= 4kHz we calculate our R2 as Tm = 0.7 X (1K + 33K) X 10 X 10^-9 = 238 ÃŽ ¼s While Space-time represents low output, Ts= 0.7 Ãâ€" R2 Ãâ€" C1 Ts = 0.7 X (1K) X 10 X 10^-9 = 0.7 ÃŽ ¼s T = Tm + Ts = 238 + 0.7 = 238.7 ÃŽ ¼s Duty cycle = = 99.7% The Quadrature Divider A quadrature divider, comprises a plurality of flip-flops, it includes at least two flip-flop, the flip-flops are interoperably coupled in series to produce a set dividing ratio 7. Each of the flip-flops includes two differential inputs I, two differential outputs O, and two differential clock inputs C, the outputs O, of one flip-flop is connected to the inputs I, of the next flip-flop, the outputs O, of the last flip-flop is connected inversely to the inputs I, of the first flip-flop, the flip-flops are clocked at their clock inputs C with differential clock signals in a consecutive manner which, for each flip-flop, are individually selected from quadrature clock input signals, 0, 90, 180, and 270, the quadrature divider is an even number divide-by-n circuit comprising a number of 2n flip-flops and providing a number of 4n output signals having 4n equidistant phases. 9 In our case the quadrature divider receives the square waveform signal from excitation oscillator as its clock signal . Figure 4 and 5 of the appendix show the pictorial representation of the quadrature divider as obtained from the circuit simulation and the oscilloscope graphic display. There are four output signals from the quadrature divider and they each have amplitude of about 5V but frequency of 1 KHz. This shows that the quadrature divider effectively divides the clock frequency into four amongst the equidistant phases. Attenuator An attenuator is a circuit that allows a known source of power to be reduced by a known factor usually expressed in decibels. The main advantage of an attenuator is that it is made from non-inductive resistors and therefore able to change a source or load, which might be reactive, into a resistive one that is know. The power reduction is achieved by the attenuator without introducing distortion. The attenuator used in our circuit is a pi type It is used to attenuate the 0 and 180 degrees antiphase 5V signal form the quadrature divider to 250mV at 1KHz. In order to get this value we need to select R5 in this attenuator circuit. Using Thevenins theorem. RTH = R5// (R3 + R4) where RTH = 100 ohms, R3 = 1K1ohms and R4 = 1K1 ohms. R5 = = 104.76 ohms. The best resistor to this to this value is a110 ohms resistor. So R5 = 110 ohms. figure 6 of the Appendix shows the graphical output of the attenuator with amplitude of about 250mV and frequency of 1 KHz. The attenuators gain in decibels is obtained by finding the ratio of the voltage corresponding to a known factor. Using the formula: , where R1 = 1100 ohms and the Z = 100, K = = 1.2 The value of attenuation, A in dB is obtained using K = 10 (A / 20) 1.2 = 10 (A / 20) A = 20 log 1.2 = 1.584 dB Instrumentation Amplifier An instrumentation amplifier is a variation of differential amplifier with input buffers that eliminates the need for input impedance matching making the amplifier suitable for use in measurement 5. It is a differential op-amp circuit providing high input impedances with the pleasure of gain adjustment through the adjustment of a single resistor. Instrumentation amplifier has very low DC offset, low drift, low noise, very high open-loop gain, very high common-mode rejection ratio, and very high input impedances. The instrumentation amplifier used in this circuit affected its accuracy and stability. The attenuated signal is applied across a resistor with very small resistance. The voltage drop across the resistor is small and needs to be amplified. The instrumentation amplifier does this, it composes of three op-amps arranged so that there is one op-amp to buffer each input signal and one to produce the desired output with adequate impedance matching for the function.3 The gain of the instrumentation amplifier circuit used for this micro-ohmmeter design is known to be 60 dB. Using the formula below then, Av =where AV = 60 dB, R = 10 k, 60 =, R9 = = 338.98 ÃŽ © The best resistor to this value is 340 ÃŽ © and it controls the gain of the instrumentation amplifier. The negative feedback of U3:A makes the voltage at pin 2 of U3:A to be equal to Voltage across R8. while, the voltage at pin 6 of U3:B is held to a value equal to Voltage across R14. This establishes a voltage drop across R9 equivalent to the voltage difference between V1 and V2 and subsequently a current through R9 and since no current is drawn by the feedback loops of the two input op-amps , the same amount of current through R9 must be going through R10 and R12 resistors above and below it. This produces a voltage drop between points A and B equal to V The ordinary differential amplifier part of the circuit then amplifies this voltage drop by a gain of 1. The post- differential amplifier circuit, with gain = R19 / R15 and differential input resistance = 2*R15. The two amplifiers on the left are the buffers. With R9 = Rgain removed (open circuited), they are simple unity gain buffers; the circuit will work in that state, with gain simply equal to R19 / R15 and high input impedance because of the buffers. The buffer gain is increased by putting resistors between the buffer inverting inputs and ground to shunt away some of the negative feedback; however, the single resistor Rgain between the two inverting inputs is a much more elegant method: it increases the differential-mode gain of the buffer pair while leaving the common-mode gain equal to 1. This increases the common-mode rejection ratio (CMRR) of the circuit and enables the buffers to handle much larger common-mode signals without clipping than would be the case if they were sep arate and had the same gain. Another benefit of the method is that it boosts the gain using a single resistor rather than a pair, thus avoiding a resistor-matching problem. The ideal common-mode gain of an instrumentation amplifier is zero. The common-mode gain of the instrumentation amplifier used in this design is near zero because of the equally numbered resistors and by the matched common-mode gains of the two buffer op-amps of the instrumentation amplifier. To obtain a closely matched resistors is difficult, as is optimizing the common mode performance of the input op-amps. All resistors are of equal value for this instrumentation amplifier except for R9. This method has the advantage of possessing extremely high input impedances on the input voltage across R=39 because they connect straight into the non-inverting inputs of their respective op-amps and adjustable gain that can be set by a single resistor. The lowest gain possible is obtained from the above circuit with R9 completely open (infinite resistance), and that gain value is 1. The output of the instrumentation amplifier is an anti-phase square wave signal from the that connects to the phase shift detector for further modification. Lock-In Amplifier A lock-inamplifier otherwise known as a phase-sensitive detector is a type of amplifier that can extract a signal with a known carrier wave from extremely noisy environment. It is a homodyne with a very low pass filter making it very narrow band. Lock-in amplifiers utilizes mixing, via a frequency mixer, to convert the signals amplitude and phase to a DC—in fact a time-varying low-frequency—voltage signal. It is often used to measure phase shift, even when the signals are of a high value and of high signal-to-noise ratio, and do not need any other improvement.To obtain signal at low signal-to-noise ratios, it is necessary that a strong, undiluted reference signal is made available at the same frequency as the signal to be measured. Phase Difference Two oscillators that have the same frequency and different phases that is, a phase difference, the oscillators are said to be out of phase with each other. The amount by which such oscillators are out of step with each other can be expressed in radians from 0 to 2Ï€ or in degrees from 0 ° to 360 °, If the phase difference is 180 degrees (Ï€ radians), then the two oscillators are said to be in antiphase. If two interacting waves meet at a point where they are in antiphase, then destructive interference will occur. It is common for waves of electromagnetic (light, RF), acoustic (sound) or other energy to become superposed in their transmission medium. When that happens, the phase difference determines whether they reinforce or weaken each other. Complete cancellation is possible for waves with equal amplitudes. Phase compensation This is the correction of phase error (i.e., the difference between the actually needed phase and the obtained phase). To obtain stability in an operational amplifier a phase compensation is required. To keep a phase margin in the phase compensation a capacitor/RC network is usually used . A phase compensator works by subtracting out an amount of phase shift from a signal which is equal to the amount of phase shift added by switching some additional amplifier stages into the amplification signal path. Low-Pass Filter A low-pass filter is a filter that passes low-frequency signals but attenuates (reduces the amplitude of) signals with frequencies higher than the cutoff frequency. An ideal low-pass filter completely eliminates all frequencies above the cutoff frequency while passing those below unchanged: its frequency response is a rectangular function, and is a brick-wall filter 8. If we need to get rid of an interfering signal in order to get a lot of attenuation, several RC filters can be cascaded. Unfortunately, the impedance of one RC section affects the next. What this means is that the transition between the pass and stop bands will not be sharp. A sharp transition helps reduce the interfering signal without causing degradation to the desired signals. In this case, the Sallen-Key active filter can do the job well. This circuit uses a 2-pole filter. Cascading a number of stages can give a steep attenuation transition with a very sharp knee. This cut-off frequency aids in selecting the R20 an d R22 resistor values to be used in the low pass filter design to average noise in the DC signal 6. The required Q for the butterworth filter = 1.414. The op-amp stage is a unity gain follower when R20 = R22. if C9 and C10 are equal, then the Q = 1.5858 for Butterworth response. Using convenient near values gain of 1.56 in the formula, R20 = R22 = Q / (4 ·Ãâ‚¬Ã‚ ·fo ·C9) where, fo = cut-off frequency = 4Hz, C9 = C10 = 0.1ÃŽ ¼F R20 = R20 = 310.31kÃŽ © The nearest standard resistor value to this calcualted resistor value is 330k Voltage Controlled Oscillator A voltage-controlled oscillator is an oscillator whose frequency is determined by a control voltage. As the control voltage causes the frequency to rise slowly until it hits a maximum and then falls back to the starting frequency. The first op-amp is an integrator(U7:A). A voltage divider puts the + input at half the control voltage. The op-amp attempts to keep its input at the same voltage, which requires a current flow across the 100k to ensure that its voltage drop is half the control voltage. When the MOSFET at the bottom is on, the current from the 200k goes through the MOSFET. Since the 100k resistor has the same voltage drop as the 100k but half the resistance, it must have twice as much current flowing through it. The additional current comes from the capacitor, charging it, so the first op-amp must provide a steadily rising output voltage to source this current. When the MOSFET at the bottom is off, the current from the 200k goes through the capacitor, discharging it, so a steadily falling output voltage is needed from the first op-amp. The result of the operation of this integrator circuit is a triangular waveform confirmed by figure 13 of the appendix. The capacitance of the capacitor in our circuit is determined thus: The second op-amp is a Schmitt trigger. It takes the triangle wave as input. When the input voltage rises above the threshold of 3.33 V, it outputs 5 V and the threshold voltage falls to 1.67 V. When the input voltage falls below that, the output goes to 0 V and the threshold moves back up. The output is a square wave. Its connected to the MOSFET, causing the integrator to raise or lower its output voltage as needed 4. Figure 14 shows the graphical representation of this circuit . The variation of the supply voltage from 3V to 9V while observing the output signal frequency obtains the sensitivity of the overall voltage- controlled oscillator circuit to supply voltage. From the test observation, the VCO produced no output signal at 3Vand beyond 6.2V. The below table shows the values obtained for the during the sensitivity test of the voltage-controlled oscillator. Using the power supply sensitivity formula Sensitivity Percentage change in frequency = Percentage change in power supply voltage = Between 5V to 6V, the percentage change in power supply voltage = = 20% While the percentage change in frequency is = 3.575% VCO sensitivity to this supply voltage variation = = 17.875 % Between 4V to 5V, the percentage change in power supply voltage = = 25% While the percentage change in frequency is = 12.21% VCO sensitivity to this supply voltage variation = = 48.84% The inference from the above calculation shows that the sensitivity of this lock-in amplifier based micro-ohmmeter to power supply voltage increases with reducing supply voltage. The tuning range of the VCO refers to the range of oscillation frequencies Two important parameters in VCO design are linearity and sweep range. Linearity correlates the change in frequency or the VCO output to the change in the control voltage. The sweep range is the range of possible frequencies produced by VCO control voltage. The linearity Muting Detector Circuit The filtered output from the phase sensitive detector is a control voltage which, with Zero input ( short circuited probes) is about Vg volts . It goes more positive with increasing signal level. With maximum input(open circuited probes) the voltage will saturate near the positive supply rail. This would result in a loud high pitched tone from the oscillator, which is not what we want. We want the it to be mute when the probes are disconnected and to do this another operational amplifier is brought in to compare the control voltage with a reference voltage. Whenever the control voltage goes higher than the reference, the output will go negative. This allows a small current to be drawn through D1 and R25, which will keep the oscillator transistor switched off, stopping oscillation. The output voltage of an AM synchronous detector is compared with a reference potential level by a voltage comparator. A muting device connected with the output of the detector is controlled by a control circuit connected with the comparator. Through this control circuit, the detector output is immediately muted when the detector output level falls below the reference potential level, and the muting of the detector output is removed after a predetermined retardation when the detector output level exceeds the reference potential level. References 1 Bateson, S. January 2010, Electronic Signal Conditioning Labs, Teesside University, Middlesbrough 2 Hewes, J, (17.02.2010), 555 Timer, http://www.kpsec.freeuk.com/555timer.htm#astable 3 Instrumentation amplifier, (14.02.2010) http://en.wikipedia.org/wiki/Instrumentation_amplifier 4 Java, (19.01.2001), Voltage controlled oscillator, http://www.falstad.com/circuit/e-vco.html 13022010 5 Kuphaldt, T, (12.02.2010), Differentiator and Integrator Circuits, http://www.allaboutcircuits.com/vol_3/chpt_8/10.html 6 Low pass filter, (14.02.2010) http://en.wikipedia.org/wiki/Low-pass_filter 7 Quadrature Divider, (17.02.2010), http://www.patentstorm.us/patents/7425850/claims.html 8 Sallen-key low-pass filter (13.02.2010), http://www.ecircuitcentezr.com/Circuits/opsalkey1/opsalkey1.htm 9 Widerin, P, (13.02.2010), Quadrature Divider, http://www.freshpatents.com/Quadrature-divider-dt20070111ptan20070009077.php