CASCADE PSEUDOMULTIBIT NOISE SHAPING MODULATORS

Cascade and multibit quantisation 1-bit feedback (NA/Dl) noise shaping modulators are presently considered the most attractive topologies fo r implementing high resolution A/D convertors. This is because the cas cade concept allows stable high order noise shaping modulators to be i mplemented easily, and because the NA/D1 architecture allows the amoun t of quantisation noise handled to be reduced while avoiding the disad vantages of using N-bit D/A convertors (N greater-than-or-equal-to 2). The work presented here proposes that cascade and multibit modulators should be seen as particular cases in a wider modulator architecture, here referred to as GaMeS. The design methodology proposed also permi ts several new modulators to be derived. All of them allow us to explo re the three parameters in the design of an A/D convertor, which are t he oversampling ratio, M, the noise shaping order, L, and the quantise r resolution, N. An analytical study is made of integrator gain and po le error effects in the SNR performance, as well as of nonidealities p resent in N-bit quantisers. Simulations made with a user-friendly and behavioural simulator we had developed, prove the correctness of the a nalyses made, and indicate that high resolution wideband A/D convertor s can take advantage of these new topologies.