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 200MHz is utilized. The effective RC time constant is controlled by the duty ratio of the 1b tuning pulse. △∑ 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 6.3kHz-step cutoff -frequency control and less than 1.8kHz of differential linearity. The transceiver is implemented in a 1.2V 90nm CMOS process.