Structure to Decrease the Number of Capacitors in Direct Sampling Mixer

Abstract

Direct sampling mixer is a kind of filters composed of a lot of capacitors and switches. The circuit realizes decimation or mixing as well as filtering by use of multi-rate clocks. Each capacitor performs roles of holding electric charge and transferring delayed voltage signal. After those roles it does not contribute to signal processing until the electric charge is reset and newly supplied charge in the next period. In other words, there are some intervals when capacitors do not work at all. Accordingly, capacitor utilization is increased by removing some capacitors and designing clock signals to keep characteristics unchanged. It achieves reduction of the number of the capacitors to allocate each capacitor plural roles.