Optimal NTF zero placement in MASH VCO-ADCs with higher order noise shaping

This paper presents a novel architecture for a multistage (MASH) voltage controlled oscillator based analog-to-digital converter (VCO-ADC). The innovation allows control over the position of noise-transfer-function (NTF) zeros, which allows to optimize the modulator's noise shaping. To achieve this, a feedback over two successive first-order MASH stages is added. Two modulator examples are elaborated. Firstly, a 2
^nd
-order MASH architecture consisting of two cascaded first-order stages (a so-called 1-1 structure) is discussed, and it is demonstrated based on computer simulations that the technique functions adequately. Afterwards, a 3
^rd
-order MASH architecture consisting of three cascaded first-order stages (a so-called 1-1-1 structure) is shown. Also here, the approach is found to operate as expected.