A programmable analog baseband filter with DC offset reduction using servo loop feedback

Abstract

SummaryThis paper presents a programmable analog baseband filter with direct current (DC) offset cancelling, using the standard complementary metal‐oxide‐semiconductor process. The servo loop feedback topology is adopted to reject in‐band DC offset at each stage of the receiving system. Furthermore, the proposed back‐to‐back diode‐connected configuration forms an ultrahigh pseudo resistor, which is applied in the feedback path of the integrator to obtain an ultralow cut‐off frequency (<1 Hz) for the high‐pass response. Therefore, low‐frequency application is possible for simultaneously in‐band DC offset and out‐band interference suppression. A servo loop feedback system with a pseudo resistor is used in the analog baseband filter to verify the concept. The chip is fabricated by using the TSMC 0.13‐um complementary metal‐oxide‐semiconductor process and consumes 43.8 mA from a 1.2 V DC supply voltage. The measured gain variation is from 65.6 to −3.3 dB with a resolution of 1 dB at a bandwidth of 5 MHz. The bandwidth is adjustable from 1.75 to 10 MHz.