Power consumption reduction in high-speed ΣΔ bandpass modulators

Power consumption is a key point in the design of high-speed switched capacitor (SC) circuits, which allow to efficiently implement a number of analog functions. Among them, SC ΣΔ modulators are very popular for A/D conversion: in this kind of circuits, operational amplifiers are the most consuming cells because of their requirements in terms of DC gain and unity-gain frequency. A new amplifier with 110 dB DC gain and a unity-gain frequency of 250 MHz is presented. The large power consumption (20 mW) makes critical its use in commercial applications: however, combining this cell with a fast adaptive biasing circuit, high performance may be achieved with a reasonable dissipation. This approach has been used in the design of a 6th-order bandpass ΣΔ modulator featuring 73 dB DR and suitable for the conversion at IF (10.7 MHz) of the FM radio signal.