A Broadband Spectrum Channelizer With PWM-LO-Based Sub-Band Gain Control

Abstract

A broadband spectrum channelizer employing pulsewidth-modulated local-oscillator (PWM-LO)-based sub-band amplitude control is demonstrated. The channelizer has an analog bandwidth of 800 MHz and partitions the input spectrum into eight contiguous sub-bands. The design employs an approach based on frequency folding from harmonics of multi-phase periodic clocks and allows for scaling the relative gain of the sub-bands over a 20-dB range. This relaxes the compression performance of the channelizer baseband and sub-analog-to-digital converter (ADC) dynamic range in the presence of large sub-bands. Gain control on individual sub-bands is performed by employing customized PWM-LO waveforms, where the PWM-LO pulses are generated using delay-locked loops (DLLs). Off-chip learning employing a neural network is used to estimate the PWM symbol pulsewidths required for setting the desired LO harmonic levels. A 1.6-GS/s spectrum channelizer integrated circuit (IC) is implemented in a 65-nm CMOS process to verify the architecture. The measured channelizer gain is 51.6–56.5 dB without gain scaling and provides a range of 37–59 dB with PWM-LO gain control. Gain scaling at a specific harmonic improves blocker compression in an unattenuated sub-band from −34 to −16 dBm. The in-band gain compression with gain scaling also increases from −32 to −17 dBm.