A 0.49-13.3 MHz Tunable Fourth-Order LPF with Complex Poles Achieving 28.7 dBm OIP3

A novel switched-capacitor low-pass filter architecture is presented. In the proposed scheme, a feedback path is added to a charge-rotating real-pole filter to implement complex poles. The selectivity is enhanced, and the in-band loss is reduced compared with the real-pole filter. The output thermal noise level and the tuning range are both close to those of the real-pole filter. These features make the filter suitable for high speed, low noise, and low power applications. A fourth-order filter prototype was implemented in a 180-nm CMOS technology. The measured in-band loss is reduced by 3.3 dB compared with that of a real-pole filter. The sampling rate of the filter is programmable from 65 to 300 MS/s with a constant dc gain. The 3-dB cut-off frequency of the filter can be tuned from 490 to 13.3 MHz with over 100-dB maximum stop-band rejection. The measured in-band third-order output intercept point is 28.7 dBm, and the averaged spot noise is 6.54 nV/root Hz. The filter consumes 4.3 mW from a 1.8 V supply.