If sampling 4th order bandpass ΔΣ modulator for digital receiver applications

Bandpass modulators sampling at high IFs (similar to200 MHz) allows direct sampling of the RF signal, reducing analog hardware, and makes it easier to realize completely software programmable receivers. This paper presents the circuit design of and test results from a continuous time tunable IF sampling 4(th) order bandpass delta-sigma modulator implemented in InP HBT IC technology for use in a multi-mode digital receiver application. The bandpass DeltaSigma modulator is fabricated in AlInAs/GaInAs heterojunction bipolar technology with a peak unity current gain cutoff frequency (f(T)) of 130 GHz and a maximum frequency of oscillation (f(MAX)) of 130 GHz. The 4(th) order bandpass DeltaSigma modulator consists of two bandpass resonators that can be tuned to optimize both wideband and narrowband operation. The IF is tunable from 140 MHz to 210 MHz in this DeltaSigma modulator for use in multiple platform applications. Operating from +/-5 V power supplies, the fabricated 4(th) order DeltaSigma modulator sampling at 4 GSPS demonstrates stable behavior and achieves a signal to (noise + distortion) ratio (SNDR) of 78 dB @ 1 MHz BW and 50 dB @ 60 MHz BW. The average SNDR performance measured on over 250 parts is 72.5 dB @ 1 MHz BW and 47.7 dB @ 60 MHz BW.