COMPUTING

Circuits with Op Amps and Non−Linear Devicessistors, and MOSFETs. In this section we will introduce just a few.Figure 5.73 shows a positive and negative voltage limiter circuit and its transfer characteristics. In thevoltage limiting circuit of Figure 5.73 the Zener diodes D 1 and D 2 limit the peak−to−peak valueof the output voltage. Thus, when the output voltage is positive, its value is limited to the valueV Z1+ V F where V F is the voltage drop across the forward−biased Zener diode and it is typicallyabout 0.7 V . Likewise, when the output voltage is positive, its value is limited to the value–( + ).V Z2V Fv out+−R 1R f−+v inV Z1V Z26.3 V+v out−D1 D 2V Z1+ V FSlope = – R f ⁄ R 1V Z2–( + )V Fv inFigure 5.73. A positive and negative voltage limiter circuit and its transfer characteristicsExample 5.20In the circuit of Figure 5.73, = = , V F = 0.7 V , R 1 = 5 KΩ , and R f = 100 KΩ .Describe the output waveforms whena.v in = 0.3sin10 tb.v in = 0.6cos100tc.v in = 3cos( 1000t + π ⁄ 6)Solution:Since this is an inverting amplifier, its gain is R f ⁄ R 1 = 100 ⁄ 5 = 20* and since we are interestedin peak values, the frequencies and phase angles are immaterial for this example. With the givenvalues, the output peaks on positive half−cycles are limited toV Z1+ = 6.3 + 0.7 = 7 Vand the output peaks on negative half−cycles are limited toV F* The gain is always expressed as a positive quantity. The minus sign simply implies inversion.Electronic Devices and Amplifier Circuits with MATLAB Computing, Second EditionCopyright © Orchard Publications5−47