Op Amps Flashcards
(28 cards)
What is the gain defined as?
A = Vout/Vin
What input resistance/impedance?
Rin = Vin / Iin (impedance r)
What does Vin equal?
(Vout*Rin)/(Rin+Rs)
Define voltage swing
The max and min voltage, determined by the power supply
What are the three golden rules/common assumptions for ideal op-amps?
1) V+ = V-
2) I+ = I- = 0
3) Output voltage is whatever it has to be to satisfy 1 and 2
What is Vout when no feedback is applied?
Vout = A0 ( V+ - V_)
What is the first order approximation of open loop gain vs frequency?
A0(f) = K/jw = K/s
What is the gain bandwidth product equal to?
Cut off freq * designed gain
What is the cut off frequency
The intersection of the low and high frequency asymptotes
The –3dB point
The gain-bandwidth product divided by the mid-band gain
What is the slew rate?
Maximum rate of change of voltage associated with the output for an op-amp
How do you avoid slew rate limiting?
dvout/dt «_space;SR
2pi*fA «_space;SR
Define full power bandwidth
max frequency at which an undistorted sine wave output can be obtained
What is saturation?
V out cannot exceed the supply voltages so levels off at v max and v min
Why would you use hysteresis?
To provide some resilience against noise
What do you ideally want the voltage swing to equal?
Vmax = 2Vs
What happens to the voltage swing if there is a significant DC offset in the output voltage?
Vmax = 2 (Vs - V off)
Why is negative feedback used?
- To minimise error
- to compensate for non ideal properties
What is the closed loop gain?
A (v) = Vout/ Vin
= 1 + R2/R1
What is the point of a buffer amplifier?
Negative feedback loop insures that inputs impedances are the same
What is the output impedance?
rout = Rout Av/ A0
What is the threshold voltage?
V thresh = +/- V sat R1/ R1R2 + VrefR2/R2R1
What is an oscillator circuit?
A schmidt trigger with a capacitor and restore
What does Vr(t) equal in an oscillator circuit?
Vr(t) = e^(-t/RC)
What does Vc(t) equal in an oscillator circuit?
Vc(t) = Vs- (vs-vc) e^(-t/RC)
