Differential Amplifiers

Why differential?

It is quite rare to find single-ended amplifiers. Why should we choose a differential amplifier over a single-ended one?

Rejection of supply noise

Fig. 57 Singled-ended amplifier.

Fig. 58 Differential amplifier cancels out voltage source noise.

Rejection of coupling

Fig. 59 Singled-ended amplifier picks up clock signal.

Fig. 60 Differential amplifier cancels out clock signal noise.

Rejection of coupling to other circuits

Fig. 61 Singled-ended amplifier couples to other circuits.

Fig. 62 Differential amplifier are layed out in such a way that parastitic capacitance is approximately the same between the two signals, cancelling each other out.

Summary

• ✅ The max swing of a differential amplifier is about double that of a single-ended amplifier.

• ✅ Even-mode distortion is suppressed.

• ❌ 2x the power consumption.

• ❌ 2x the area (footprint).