Programmable Order Multiple Feedback Band-Pass Active-RC filter for FSK Transceiver

An integrated programmable order multiple feedback (MFB) band-pass filter (BPF) implemented in 0.14 um CMOS technology is presented. The modular single ended filter has been used in an FSK transceiver, in both receiver (RX) and transmitter (TX). It is implemented by cascading different types of BP filters with different required bandwidth (BW) of RX and TX. A combination of Bessel and Butterworth filters to maximize stop-band rejection, optimize in-band flatness and minimize group delay variation is used. Each stage of the MFB filter draws 0.3mA of current from a 1.8V supply. A simple and efficient approach to trim center frequency which has minimum impact on area and parasitic components has been used. AC gain change of TX due to mismatches, parasitic and process and trimming has been compensated by a simple gain stage while it is budgeted in RX system SNR. The implemented 23.2MHz center frequency filters have been used in the FSK transceiver of a USB power delivery (PD) system, with a BW of 3.46MHz for RX filter and a BW of 1.3MHz for TX filter. The employed low current and small area architecture with its efficient trimming strategy meets the required performance of the FSK transceiver.