| This thesis investigates high performance building blocks for switched-current circuits in digital-CMOS processes. The building blocks, called memory cells, are designed to have low charge-injection and hence low harmonic distortion. Low charge-injection in the memory cells is achieved by using a technique called the constant-voltage switching technique. This technique is based on the operation of the switches in the memory cell at a virtual-ground node. This results in near signal-independent charge-injection and causes a constant voltage offset. This voltage offset is rejected using a fully-differential scheme. Two types of memory cells, one with virtual-ground nodes at drains of transistors, named the virtually-grounded drain (VGD) cell, and the other with virtual-ground nodes at sources of transistors, named the virtually-grounded source (VGS) cell, are studied. Various topologies for these cells are developed and their aspects analyzed and verified through simulation.; In order to demonstrate the efficacy of the constant-voltage switching technique, a fully-differential, 3rd order switched-current elliptic lowpass filter with memory cells based on the VGD scheme, is designed, fabricated and tested. The filter is designed for a nominal clock frequency of 10MHz and a cut-off frequency of 1MHz and consumes 29mW of power. The experimental transfer function of the filter matches its ideal transfer function to a very high degree, thus demonstrating the accuracy of SI circuits. The prototype filter also shows a good harmonic distortion of over −57dB for inband current signals of amplitude 300μA-peak differential (corresponding to a 50% modulation index). This illustrates that the problem of charge-injection is solved to a high degree. |
