A power-efficient high GBW operational amplifier with its analog baseband IC implementation in 40-nm CMOS technology

This paper presented a power-efficient, relatively high voltage gain, high GBW (gain-bandwidth-product) operational amplifier (OPAMP) with a pole cancellation technique and adaptive common-mode (CM) bias circuit. A typical two-stage topology is adopted in the OPAMP prototype design while the 1st amplifier stage is in class-A mode for high voltage gain and the 2nd buffer stage is in class-AB mode for both large drive capability and additional voltage gain. In order to improve GBW and set appropriate CM voltages, an actively biased resistor-capacitor pair is inserted in between the two stages with the overall frequency response of the OPAMP nearly unaffected. Thus, a little increase in area and power consumption is traded for pole cancellation while adaptive CM bias circuits are introduced to critical current-biased transistors with the outcome of excellent CM voltage stability across all process, voltage, temperature corners. In order to verify the practicality of the proposed OPAMP, a fully programmable analog baseband IC is designed with three key blocks, including trans-impedance amplifier, LPF (low pass filter)/HPF (high pass filter)/PGA (programmable gain amplifier) hybrid bi-quads, test buffer and power supply management units, and its - 3 dB bandwidth with voltage gain is fully programmable. What is more, two class-AB power efficient PMOS-only buffers are designed to ensure input and output test adaptability. Fabricated in a 40-nm Bulk CMOS process, the chip prototype achieves an LPF's - 3 dB bandwidth of 28-35 MHz with 3-bit digital control and 1 MHz/step programmability, an HPF's - 3 dB bandwidth of 3-15 MHz with 3-bit digital control, and a voltage gain of 0-63 dB with 6-bit digital control and 1 dB/step programmability. With a 20 dB voltage gain, HPF corner at 3 MHz and LPF corner at 35 MHz, the measured output P-1 dB is 12.1 dBm@20 MHz, and the output IP3 is 21.1 dBm@20 MHz. The total current consumption is around 3 mA@1.5 V and 2 mA@2.5 V.