Design and Verification of a Switchable Opamp for Switched-Capacitor Integrators

A switchable operational amplifier (opamp) is examined in this brief. It is based on a current-mirror opamp with switchable transconductance values. Contrary to switched opamp (SO) and partial SO, it can be used to realize both half-delay and full-delay switched-capacitor integrators. The added circuit design complexity is shown to be minimal. Optimal switching is developed in this brief. It is also shown in this brief that the absolute average power consumption can be less as compared with an SO design. The experimental results of a delta-sigma modulator prototype (designed in 1-V 65-nm CMOS), employing the designated switchable-opamp technique, show power reduction without any degradation in SNDR (58.5 dB) or SFDR (67 dB).

[1]  Jian Xu,et al.  Ultra low-FOM high-precision ΔΣ modulators with fully-clocked SO and zero static power quantizers , 2011, 2011 IEEE Custom Integrated Circuits Conference (CICC).

[2]  Howard C. Luong,et al.  A 1-V 3.5-mW CMOS switched-opamp quadrature IF circuitry for Bluetooth receivers , 2002, VLSIC 2002.

[3]  F. Maloberti,et al.  Digitally-enhanced 2nd-order ΔΣ modulator with unity-gain signal transfer function , 2008, 2008 IEEE International Symposium on Circuits and Systems.

[4]  R. Castello,et al.  A 1 V 1.8 MHz CMOS switched-opamp SC filter with rail-to-rail output swing , 1997, 1997 IEEE International Solids-State Circuits Conference. Digest of Technical Papers.

[5]  Michiel Steyaert,et al.  Switched-opamp: an approach to realize full CMOS switched-capacitor circuits at very low power supply voltages , 1994, IEEE J. Solid State Circuits.

[6]  Michel Steyaert,et al.  Converter with 77-dB Dynamic Range , 1998 .

[7]  Chien-Hung Kuo,et al.  A Low-Voltage Fourth-Order Cascade Delta–Sigma Modulator in 0.18-$\mu\hbox{m}$ CMOS , 2010, IEEE Transactions on Circuits and Systems I: Regular Papers.

[8]  Anas A. Hamoui,et al.  A current-mirror opamp with switchable transconductances for low-power switched-capacitor integrators , 2013, 2013 IEEE International Symposium on Circuits and Systems (ISCAS2013).

[9]  W. Sansen,et al.  A 900-mV low-power ΔΣ A/D converter with 77-dB dynamic range , 1998, IEEE J. Solid State Circuits.