Switched-Capacitor, Low-Pass FilterTargets Battery-Operated Products

In conventional operation, the MSELP, a switched-capacitor, elliptic low-pass filter, has a typical supply current of 1 mA with a maximum corner frequency of 20 kHz at a 100:1 clock-to-corner ratio. In its low-power mode, the filter has a typical supply current of 600 µA with a maximum corner frequency of 5 kHz; in power-down mode, the device rests at a typical supply current of 250 µA. The MSELP operates at 5V, ±10%, or 3V, ±10%. Applications are two-way mobile radio systems such as land mobile radio and family radio service to filter out the voice signal while preserving the low-frequency signaling tones. Because the signaling tones and the voice signal are close together, the sharp roll-off and the stop-band rejection of the MSELP can remove the voice signal without damaging the signaling tones.