Noise shaping achieved using spectrum where it can be removed by the digital filter. In general, over-sampling alone is not enough to achieve the required resolution. Thus the noise density in the band of interest is much reduced. The modulator over-samples the input and spreads the quantization noise from DC up to a bandwidth of fs/2. It also minimizes the effects of component drift with time making the sigma-delta very stable compared with other architectures. This action forms a high gain, negative feedback loop which gives the sigma-delta ADC excellent linearity and no missing codes. Any deviation will quickly result in the average bit-stream density from the comparator being adjusted to follow the analog input signal. The average density of the bit-stream closely tracks the analog input signal. This is then integrated and enters a comparator that outputs a 0 or 1 depending on whether the output of the integrator is below or above the comparator's threshold. With the circuit shown in figure 2, the analog input signal and a bit-stream whose 1's bit density is a representation of the magnitude of the analog signal are fed into a summing amplifier. This procedure is essentially a digital process and the linearity performance is determined by the sampling capacitor. The feedback works to minimize the error between the input signal and the feedback signal. The analog modulator consists of a sampling capacitor and a 1-bit A/D converter in an analog negative feedback loop with high open loop gain. A model for a typical first order sigma-delta modulator is illustrated in Figure 2.įigure 2. This one bit data stream is processed by a digital filter to produce a high resolution conversion result. The sigma delta modulator samples the analog input at many times the Nyquist rate and produces a 1-bit output whose average value tracks the analog input. The main components of a sigma delta converter are a sigma delta modulator and a digital filter as shown in Figure 1. Source: Sigma delta conversion is a technique that has gained popularity for high-resolution applications. Back to library What is a sigma delta converter and how does it function?
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