Problem Statement – Why is this opamp circuit not amplifying over the entire range?
VDD = 3.3 V, IBIAS = 1uA; ICMR = 0V-2.4 V, Output CMR = 0.2V – 3.1V
With the opamp that I designed (which gives unloaded gain of 80 dB and loaded (RL =10K; CL = 12pF), the dc input is amplified till only 550mV above which output saturates at around 1.9V as shown in fig 1.
Re: Why is this opamp circuit not amplifying over entire ran
Ideal opamp has maximum swing at output that is between -ve and +ve supply voltages. But, real opamps not. So, your circuits has real opamp and output voltage can not reach 3.3V, it stops at ~1.9V.
If you want increase output voltage range, just increase supply voltage or use rail-to-rail opamp.
Re: Why is this opamp circuit not amplifying over entire ran
happy2005 said:
Ideal opamp has maximum swing at output that is between -ve and +ve supply voltages. But, real opamps not. So, your circuits has real opamp and output voltage can not reach 3.3V, it stops at ~1.9V.
If you want increase output voltage range, just increase supply voltage or use rail-to-rail opamp.
Re: Why is this opamp circuit not amplifying over entire ran
I think that you don't have big enough current capacity on output. You use 498u to suply feedback, and I don't think that your amplifier can suply more. That's why you enter in saturation mode when you try to raise voltage at output (biger voltage means biger current).
For solution I have to see topology of amplifier.
amic
I agree with happy2005.
as i know, there are 2 type of opamp [from point of view output topology], full swing (or rail to rail) and normal type.
in normal type maximum output voltage are ≈[VCC - (1.5-3)] Volt.
and minimum output voltage are ≈[VEE + (0-1)] volts.
and they are unbalanced.
for more information you can refer to internal circuit of your opamp.