Decreasing the effects of BJT's parasitics of computing cells for analog decoders

Abstract

This paper presents an analog decoder computing cell less sensitive to bipolar jnnction transistor (BJT) parasitic elements. Unlike customary cells, the proposed cell does not invert the output probabilities ranking, hence limiting the wrong decoding outcome. This is achieved with a slight complexity increase as only two diodes are added to the basic computing cell. It is also shown that the proposed cell can improve the decoding performance even for large biasing current, opening the way to improve the decoding convergence of an analog BiCMOS decoder. Simulation results are shown for a O.25-p,m BiCMOS process from NXP with minimal size transistors.

Trade-off between surface, biasing current and performance of an analog turbo decoder

“…However, it has been shown in [6] that the parasitic emitter resistor R E of BJTs can significantly alter the conversion of LLRs into probabilities. The collector current is thus better described by:…”

“…No work has been published studying the effect of non random effects like parasitic emitter resistor and biasing current on the performance deterioration of BJT-based analog decoding in term of BER. It has only been shown in [6] that the parasitic emitter resistor R E of BJTs can significantly alter the conversion of Log-Likelihood Ratios (LLR) into probabilities. The study was limited to the computing cells and the performance of a decoder was not assessed.…”