A Multirate Switched-Current Filter Using Class-AB Cascoded Memory

Switched-current (SI) techniques for modern short-range wireless filters are described. The cascoded Class-AB SI is employed for improved memory accuracy with minimum loss of overall performance. With emphasis on low power, a multirate SI scheme that features order reduction and simple interfacing of the continuous-time anti-alias filter to the sampled data SI filter is introduced. Implemented using a 3-V 0.35-mum digital CMOS process, the fifth-order complex bandpass SI filter was designed and optimized at 2.0-V supply voltage for Bluetooth application with 1-MHz center frequency and 1.2-MHz bandwidth. It has a voltage gain of 20.5 dB and achieves an image rejection of 45 dB, a spurious-free dynamic range of 64 dB and the signal-to-noise ratio of 67 dB