A robust CMOS compander circuit meeting all of the requirements for analog cellular telephony and using an improved sigma-delta compander topology is presented. Rather than digitizing and reconstructing the input signal using a sigma-delta modulator as has been done previously, only the amplitude path is digitized while the voice path remains analog. The amplitude information is obtained digitally, and is reduced to a single bit using a first-order sigma-delta modulator. Performing this function digitally eliminates problems due to analog offsets and in implementing the long time constant required. The output signal is formed by gating the analog input signal under control of the amplitude signal. The expander and compressor circuits each consist of a single op amp and 2000 gates of digital logic, and have been implemented on 0.8-/spl mu/m CMOS processes. The ADC for the amplitude path uses a compact switched-capacitor second-order sigma-delta modulator implemented using a single amplifier. No external components are required. Tracking error for the compressor was measured to be less than 0.3 dB over a 60-dB input range when operating on a 3.0-V supply. The test time, when compared to conventional compander implementations, is considerably reduced.
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机译：提出了一种健壮的CMOS压缩扩展器电路，该电路可以满足模拟蜂窝电话的所有要求，并使用改进的sigma-delta压缩扩展器拓扑。与其像以前那样使用sigma-delta调制器对输入信号进行数字化和重构，不如仅对幅度路径进行数字化而语音路径保持模拟。振幅信息是通过数字方式获得的，并使用一阶sigma-delta调制器将其减小到一位。以数字方式执行此功能可消除由于模拟偏移和实现所需的长时间常数而引起的问题。通过在幅度信号的控制下对模拟输入信号进行门控来形成输出信号。扩展器和压缩器电路每个都由一个运算放大器和2000个数字逻辑门组成，并已在0.8- / spl mu / m CMOS工艺上实现。用于幅度路径的ADC使用紧凑的开关电容器二阶sigma-delta调制器，该调制器使用单个放大器实现。无需外部组件。在3.0V电源下工作时，在60dB输入范围内，压缩机的跟踪误差测得小于0.3dB。与传统的压缩扩展器相比，测试时间大大减少了。
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