Digitizing Considerations Typical A/D system Specs Accuracy Linearity Precision Monotonicity Resolution/Dynamic Range Timing Aperture Delay Jitter Settling Maximum Rate (Conversion Time) Temperature Coefficient Noise

A/DD/A N Bit value: Q Digital Channel v in vv v out v in (max) v in (min) - + v in Quantization Noise

If the sampled signal has known S/N S, then it doesn’t make sense to choose a quantization resolution such that S/N Q >> S/N S Let v in be a sinusoid with amplitude Quantization S/N This is the best S/N. If the signal amplitude is half the max amplitude, S/N degrades by 3 dB.

Companding (Compressing/Expanding) A trick to maintain consistent S/N over a wide dynamic range:  – Law Companding Curve v in v out up/dn’.. +_+_ DAC  -1 Binary Counter Digital Data Analog Tx Analog Rx Companding Codec (Coder/Decoder)

PCM –TDM (Time Division Multiplexing) Channel 1 n bits Channel 2 n bits Channel M n bits.. f framing bits 1 Data Frame = (nM + f ) bits Since one frame contains one sample of each channel, the frame rate must equal the sample rate.