CMOS switched-capacitor DSB-SSB converter using Hilbert transformer

Resumo

The realization of an analog integrated circuit for conversion of double-sideband (DSB) amplitude-modulated signals into single-sideband (SSB) is presented. The converter is implemented by discrete-time switched-capacitor (SC) circuits, and it adopts structurally all-pass filters to realize a Hilbert transformer with low sensitivity to capacitor mismatch. The use of variable-gain amplifiers in place of frequency mixers greatly reduces circuit complexity and associated non-linearities. The chip is fabricated in a 180 nm CMOS technology with metal-metal (MiM) capacitors. For 1.8 V power supply and 1 V differential input/output signals, experimental results show the converter achieves image rejection ratio (IRR) greater than 39.5 dB for lower-sideband (LSB) modulation and 38.0 dB for upper-sideband (USB) modulation with input frequency ranging from 25% to 75% of the carrier frequency. Its silicon area is 1.09 mm² and the converter consumes only 17.7 mW for 1 MHz sampling frequency while its IRR presents standard deviation of only 0.5 dB among 20 chip samples without any circuit trimming.