Differential Amplifier is an electronic circuit which amplifies the difference between two input voltage, but rejects any signal common to both the inputs [Source].
Following is the circuit for Designing a Differential Amplifier-
© Copyright – Gautam Vashisht
You may also face these questions while designing a differential amplifier.
Differential Amplifier can be designed by following 5 simple steps –
Step 1:
Assume some specifications such as the Gain Bandwidth, Slew-rate, Load Capacitance, ICMR range etc. for designing the differential amplifier accordingly.
Step 2:
Determine the technology-dependent parameters like VDD, threshold voltage of pMOS and nMOS (Vtp and Vtn), µnCox , µpCox etc. from the model files in the circuit simulation tool used. Using the standard equations, determine the value of drain current.
Step 3:
Find (w/L) ratio of the top 2 transistors (M3 & M4) using the above assumed ICMR (max) value, (w/L) ratio of the middle 2 transistors (M1 & M2) using the assumed Gain Bandwidth product value, and (w/L) ratio of the bottom 2 transistors (M5 & M6) using the assumed ICMR (min) value.
Step 4:
Finally, test the circuit with the above determined values in a circuit simulation tool such as Cadence or ADS etc. & determine the values of the parameters you assumed in Step 1 from the tool.
Step 5:
If they come out to be approximately equal to that you assumed, you are done! (but you can still improve the circuit if you want).
If they do not come out to be what you assumed, check your calculations, values of technology-dependent tool parameters & the values you entered in the circuit simulation tool.
Gautam Vashisht