S/N Optimized, Programmable 1–10 MHz Bandwidth and 0–20 dB Gain, Precision I-Q Communication Channel for Digital Video Applications

Abstract

An analog part of a digital-video quadrature demodulation scheme is built using a 7 GHz, 0.8 μm biCMOS process. The scheme provides for 1–10 MHz cutoff frequency and 0–20 dB gain controls and dissipates 250 mW from a power supply of 5 V. The channel filtering is realized by two identical 4th Order Butterworth lowpass filters built with the g_m - C technique. They are equipped with cutoff programming and in-package trim tuning for cutoff adjustment. A programmable gain amplifier is placed in front of each filter for better joint noise and intermodulation performance. Such an arrangement allows to operate the filter at a maximum signal level improving the worst-case channel S/N by 6.5 dB. For the in-band components the worst case S/N is better than 41 dB, whereas THD and IMD are less than - 48 dB. This single-ended channel achieves PSRR of 42 dB.