Op Amps Flashcards
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)
What is the aiming potential?
- When Vc tends to Vs as t tends to infinity. Vc(infinity) is known as the aiming potential
- will be + Vsat or - Vsat
What is the value of input impedance for an ideal operational amplifier?
Infinite
What is the value of output impedance for an ideal operational amplifier?
Zero
What is the value of open loo gain for an ideal operational amplifier?
Infinite
