Determining the output swing, output common-mode range and input common-mode range in a differential amplifer
I am currently learning amplifier design, after constructing the unity gain amplifier(which is a differential-input single-ended-output amplifier) in the unity-gain feedback configuration I have performed a DC sweep of the input common-mode voltage from 0 to 2.4V. Below is the circuit and plot for output voltage with the DC sweep input. How to figure out the input common-mode range, output common-mode range, and output swing from the plot? The resistive load value is 125 Kohms.
-
As per the meaning I understood of input common-mode range, it is the input range for which output will not be clipped. So that means is it the linear voltage from 0.4 V to 1.3 V as we are using unity gain?
-
As per the meaning I understood of output swing, the max output voltage range where it is not clipped. That means the same linear portion from the plot shown below i.e. 0.4 V to 1.3 V.
-
As per the meaning I understood of output common-mode range,it is the same as output swing.
If my understanding is wrong kindly educate me and I request to elaborate to figure this out. Below are the screenshots of the circuit, schematic using the circuit as a symbol and plot.
1 answer
First, common mode is something that only applies to a differential signal. When a signal is encoded in the difference between two voltages, the common mode voltage is the average of the two.
The common mode range is the range of common mode voltage over which a small differential signal can still be correctly detected.
The output swing is as you say, the maximum range the output voltage can vary while still being the expected function of the input voltages.
Common mode output range makes no sense, since the output is single-ended, not differential.
Your plot is unreadably small and the axis poorly defined, so I can't comment on how the above relates to your measurements.
1 comment thread
1 comment thread