Oscillators With the addition of a capacitor and resistor, the Schmitt trigger can be turned into a simple oscillator. Technically, it’s known as an astable.
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Presentation on theme: "Oscillators With the addition of a capacitor and resistor, the Schmitt trigger can be turned into a simple oscillator. Technically, it’s known as an astable."— Presentation transcript:
1 OscillatorsWith the addition of a capacitor and resistor, the Schmitt trigger can be turned into a simple oscillator.Technically, it’s known as an astable multivibrator.Before looking at the circuit, it is worth reviewing the transient response of a first order RC network.
3 is a separable first order differential equation. These are the easiest kind to solve!First, rearrange:and integrate each side:The constant, , is the value of VR when time=0, so:
4 VCtVSVC(0) > VSVC(0) < VSNB. In either case, VC ® VS as t ® ¥. VC(¥) is known as the aiming potential.
5 Oscillator CircuitThe op-amp, R1 and R2 form an inverting Schmitt triggerAs R1 = R2, threshold levels are ±VSAT/2The output is fed-back to the inverting input via an RC networkThe aiming potential of the capacitor voltage will be either +VSAT or –VSAT
7 AnalysisTo calculate the time-period, consider just one half-cycle of the oscillation.VVSATt-VSAT
8 Analysis (cont) V t Half-cycle ends when VC reaches VSAT/2 VSAT -VSAT t-VSATFull period of oscillation is 2 half cycles,
9 Oscillator SummaryUsing only a couple of extra components, the Schmitt trigger can be converted into a simple oscillatorR & C set the period of oscillation independently of VSATMany square wave oscillators work using the same basic principles
10 Active Feedback Components There are two broad categories of non-linear op-amp circuitsThose that exploit saturationThose that use active components in the feedback networkWe will concentrate on one example of the latter genre – the precision rectifier
12 Precision rectifier Note that: The current through the diode (and therefore also through RL) can only flow in one directionThe load voltage, VOUT, cannot, therefore, go below 0 VWhen the diode conducts, VOUT » V1 - ½
16 Other Non-Linear Applications Circuits that effectively change the saturation level(s) of the op-amp.Precision rectifierLimitersCircuits that use the exponential V-I curve of PN junctions.Log and antilog amplifiersMultipliers, squarers and dividers
17 Summary Non-Linear applications of op-amps Essentials ComparatorSchmitt TriggerPrecision RectifierAdditions for interestLimitersLog/antilog ampsMultipliers etc.