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.