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

This 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 (<1Hz) 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 43.8mA from a 1.2V DC supply voltage. The measured gain variation is from 65.6 to -3.3dB with a resolution of 1dB at a bandwidth of 5MHz. The bandwidth is adjustable from 1.75 to 10MHz.