A 90nm CMOS CT BPF for Bluetooth transceivers with DT 1b-switched-resistor cutoff-frequency control

摘要

In this paper, a scheme for tuning cutoff-frequency of filters is presented. Instead of using a multibit resistor bank, a 1b switched-resistor structure operating at 200 MHz is utilized. The effective RC time constant is controlled by the duty ratio of the 1b tuning pulse. DeltaSigma modulation with dithering mitigates the spurious effects. Compared to the conventional tuning scheme, finer cutoff frequency tuning and more linear control are achieved. The tuning scheme is applied to a channel-select filter in a Bluetooth transceiver resulting in 6.3 kHz-step cutoff -frequency control and less than 1.8 kHz of differential linearity. The transceiver is implemented in a 1.2 V 90 nm CMOS process.