# Help with implementation of circuit in LTSpice

#### Alec_t

Joined Sep 17, 2013
11,285
Welcome to AAC!
The nice thing about a simulation is that you can choose component values and see what happens without frying anything.
What is the frequency of your signal Vg?
For starters, I'd suggest :-
Choose C∞ to have a reactance which is much smaller than R1 at that frequency.
Replace I1 with a voltage source as per the reference circuit.
Choose a supply voltage (Vcc).
Choose Vcm to be around Vcc/2 (for both Q1 and Q2 base bias inputs).
Keep Vg peak-to-peak voltage less than Vcm to avoid waveform clipping.
Choose R2 to give a bias current of, say, 100uA.
Have fun!

#### robi10101298

Joined May 7, 2020
9
Welcome to AAC!
The nice thing about a simulation is that you can choose component values and see what happens without frying anything.
What is the frequency of your signal Vg?
For starters, I'd suggest :-
Choose C∞ to have a reactance which is much smaller than R1 at that frequency.
Replace I1 with a voltage source as per the reference circuit.
Choose a supply voltage (Vcc).
Choose Vcm to be around Vcc/2 (for both Q1 and Q2 base bias inputs).
Keep Vg peak-to-peak voltage less than Vcm to avoid waveform clipping.
Choose R2 to give a bias current of, say, 100uA.
Have fun!
Hello, thanks for the answer! VCC= 10V;VCM = 1.5V;vg is a sine wave with a frequency of 1 kHz. Its amplitude will be chosen so as to ensure minimal distortion of the output signal (i.e. voshould also be a sine wave); R1= 15kΩ ;
I need to: a)Calculate the theoretical expressions of the DC collector currents of bipolar transistors Q1–Q8, considering VBE≈ 0.6V. Calculate the theoretical expression of the small-signal voltage gain Av= vo/vg.
b)Implement the schematic in a circuit simulation software (LTSpice). Design the circuit (i.e. select transistor types for Q1–Q8, choose a value for R2and C∞) in order to have a(theoretical)gain value Av= 1000 + 2 ∙ 250,
c)Simulate the circuit(transient, AC sweep), choosing an appropriate amplitude for vg in order to minimize output signal distortion.
d)Compare the theoretical Av value from point b) with the value obtained from the simulation. Name a possible cause for differences between the two values.
e)Specify a method for decreasing the voltage gain (without changing R1, R2, VCC or VCM). Implement the change and re-simulate the circuit in order to demonstrate the effect.