
Operational Amplifi ers
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2.3 Telescopic and Folded-Cascode Op-Amps
Telescopic and folded-cascode op-amps belong to the cascode op-amp topologies,
where multiple transistors are stacked up to increase the total output impedance,
which in turn boosts the op-amp’s intrinsic dc gain value. A telescopic CMOS op-
amp and a folded-cascode CMOS op-amp are shown in Figures 2.2 (a) and (b),
respectively. Both are fully differential confi gurations while the common-mode
feedback (CMFB) circuits are not shown for simplicity.
Let us start with the telescopic op-amp shown in Figure 2.2(a) [3]. Specifi cally,
note that the unity-gain bandwidth (i.e., the dominant ...