Category Archive for: SPECIAL PURPOSE CIRCUITS

The 8038 Clntegrated Circuit Function Generator

Function generators capable of producing sinusoidal, triangular, and rectangular waveforms are commercially available in integrated-circuit form. An example is the 8038, manufactured by Intersil as the ICL8038 and also available from other manufacturers. This versatile circuit is capable of generating the aforementioned waveforms simultaneously (at three separate output terminals) over a frequency range from Hz to 1 MHz. Frequency is…

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FM Demodulation

Recall that frequency modulation (FM) is the process in which the frequency of one signal is controlled by the magnitude of another signal. A yea generates an FM signal, as illustrated in Figure 15-37. In this example, the input to the yea (the modulating signal) ia a ramp voltage whose amplitude increases with time Consequently, the output of…

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Phase Lockedloops

A phase-locked loop (PLL) is a set of components that, through the use of feedback, generate a signal whose frequency tracks that of another externally connected input signal. The term phase-locked is derived from the fact that the (apparent) phase difference between two signals of different frequencies is used to control, or maintain, the frequency of the output, as…

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TRANSCONDUCTANCE AMPLIFIERS

A transconductance amplifier is basically a voltage-controlled current source. As shown in Figure 15-28. the amplifier typically has a differential input and singleended output. Recall that transconductance is defined to be output current divided by input voltage. The transconductance of the amplifier. A programmable transconductance amplifier is one whose value of gm is determined by the value of an…

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LOGARITHMIC AND ANTILOGARITHMIC AMPLIFIERS

A logarithmic (log) amplifier produces an output that is proportional to the logarithm of its input. Since the log function is nonlinear, it is clear that a log amplifier is not linear in the sense discussed in Chapter 3. A logarithmic transfer characteristic is shown in Figure 15-24. We see that the slope of the characteristic,and hence the…

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CLAMPING CIRCUITS

Clamping circuits are used to shift an ac waveform up or down by adding a de level equal to the positive or negative peak value of the ac signal. In the author’s opinion, “clamping;’ is not a particularly good term for this operation: Level shifting is more descriptive. Clamping circuits are also called dc level restorers because…

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Precision Rectifying Circuits

Recall that a rectifier is a device that allows current to pass through it in one direction only. A diode can serve as a rectifier because it permits generous current flow in only one direction-the direction of forward bias. Rectification k +,he same as clipping at the 0-V level: all of the waveform below (or above) the zero-axis is…

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Clipping Circuits

In Chapter 5, we referred to clipping as the undesirable result of overdriving an amplifier. We have seen that any attempt to push an output voltage beyond the limits through which it can “swing” causes the tops and/or bottoms of a waveform to be “clipped” off, resulting in distortion. However, in numerous practical applications, including waveshaping and nonlinear function…

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An Astable Multivibrator

The word astable means “unstable,” and, like other unstable devices, an astable rnultivibrator is a (square-wave) oscillator. (A bistable multivibrator, also called a flip-flop, is a digital device with two stable stages; a monostable multivibrator h:> one stable state, and an astable mu1tivibrator has zero stable states.) An ,W;’ multivibrator can be constructed by using an operational amplifier as…

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Hysteresis and Schmitt Triggers

In its most general sense; hysteresis is a property that means a device behaves differently when its input is increasing from the way it behaves when its input is decreasing. In the context of a voltage comparator, hysteresis means that the output will switch when the input increases to one level but will not switch back until the input…

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