![]() This paper presents a new Zener diode compact model that accounts for frequency band limited shot and flicker noise, and resister thermal noise in the time domain. Zener diode transient noise simulation adds an important tool to the available circuit design and analysis repertoire. The omission of a simple method for time domain noise generation was a serious limitation because Zener diodes are often a central component in the design of low cost noise generator circuits for test equipment, particularly analogue dithering signal generation for A/D dynamic range analysis, spectrum analyser calibration, and communications receiver performance testing under fading and EMI conditions. 8 These tools support time domain noise generation as a transient simulation progresses. Today this situation has changed through on-going improvements to freely available circuit simulation tools, including Ngspice, 6 Xyce, 7 and Qucs-S. Such an approach is not very practical for noise because it is very inflexible and potentially error prone. Early versions of SPICE did not implement a simple method for time domain noise generation but relied on piece-wise linear sources for complex signal waveform construction. There is at least one application area where the existing Zener diode models are inappropriate. Moreover, it is common practice for device manufacturers to characterise SPICE models for their products. or low frequency analogue signal processing, for example, voltage stabilisers and wave shaping circuits, the improved Zener diode models have acceptable functionality and accuracy. For a high percentage of the Zener diode applications at d.c. Of particular interest is the paper by Deveney 5 that presents a temperature dependent macro-model for Zener and avalanche diodes. Piotrowski also added a series resistance in the Zener or avalanche breakdown regions improving model performance at high diode currents. The 1988 paper by Piotrowski 4 reported a reverse diode model that improved modelling of low leakage currents. To ensure numerical stability a new limiting algorithm was implemented and merged with the SPICE simulator code. This extension was added to the original SPICE 2 diode model. In 1981 Laha and Smart 3 introduced a breakdown mechanism modelled as the sum of exponential terms. Since the SPICE Zener diode model was first released a series of publications have reported improvements to its simulated d.c. It has a number of limitations however, including poor reverse bias leakage current accuracy, a common series resistance for both the high current forward and reverse bias regions of operation, limited control of the slope of the Zener or avalanche breakdown regions and no mechanism for setting temperature variation of the Zener or avalanche breakdown voltage. The SPICE 1, 2 diode model is a core element in Zener and avalanche breakdown diode modelling.
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