CS5016 datasheet(25/40 Pages) CIRRUS

25 / 40 page

Since bits (and their errors) switch in and out

throughout the transfer curve, their effect is sig-

nal dependent. That is, harmonic and

intermodulation distortion, as well as noise, can

vary with different input conditions. Designing a

system around characterization data is risky since

transfer curves can differ drastically unit-to-unit

and lot-to-lot.

The CS5012A/14/16 achieves repeatable signal-

to-noise and harmonic distortion performance

using an on-chip self-calibration scheme. The

CS5012A calibrates its bit weight errors to a

small fraction of an LSB at 12-bits yielding peak

distortion below the noise floor (see Figure 18).

The CS5014 calibrates its bit weights to within

±1/16 LSB at 14-bits (±0.0004% FS) yielding

peak distortion as low as -105 dB (see Fig-

ure 21). The CS5016 calibrates its bit weights to

within

±1/4 LSB at 16-bits (±0.0004% FS) yield-

ing peak distortion as low as -105 dB (see

Figure 23). Unlike traditional ADC’s, the linear-

ity of the CS5012A/14/16 are not limited by

bit-weight errors; their performance is therefore

extremely repeatable and independent of input

signal conditions.

Quantization Noise

The error due to quantization of the analog input

ultimately dictates the accuracy of any A/D con-

verter. The continuous analog input must be

represented by one of a finite number of digital

codes, so the best accuracy to which an analog

input can be known from its digital code is

±1/2 LSB. Under circumstances commonly en-

countered in signal processing applications, this

quantization error can be treated as a random

variable. The magnitude of the error is limited to

±1/2 LSB, but any value within this range has

equal probability of occurrence. Such a prob-

ability distribution leads to an error "signal" with

an rms value of 1 LSB/

√12. Using an rms signal

value of FS/

√8 (amplitude = FS/2), this relates to

ideal 12-, 14-, and 16-bit signal-to-noise ratios

of 74, 86, and 98 dB respectively.

Equally important is the spectral content of this

error signal. It can be shown to be approximately

white, with its energy spread uniformly over the

band from dc to one-half the sampling rate. Ad-

vantage of this characteristic can be made by

judicious use of filtering. If the signal is ban-

dlimited, much of the quantization error can be

filtered out, and improved system performance

can be attained.

FFT Tests and Windowing

In the factory, the CS5012A/14/16 are tested us-

ing Fast Fourier Transform (FFT) techniques to

analyze the converter’s dynamic performance. A

pure sinewave is applied to the CS5012A/14/16,

and a "time record" of 1024 samples is captured

and processed. The FFT algorithm analyzes the

spectral content of the digital waveform and dis-

tributes its energy among 512 "frequency bins."

Assuming an ideal sinewave, distribution of en-

ergy in bins outside of the fundamental and dc

can only be due to quantization effects and errors

in the CS5012A/14/16.

If sampling is not synchronized to the input sine-

wave, it is highly unlikely that the time record

will contain an integer number of periods of the

input signal. However, the FFT assumes that the

signal is periodic, and will calculate the spectrum

of a signal that appears to have large discontinui-

ties, thereby yielding a severely distorted

spectrum. To avoid this problem, the time record

is multiplied by a window function prior to per-

forming the FFT. The window function smoothly

forces the endpoints of the time record to zero,

thereby removing the discontinuities. The effect

of the window in the frequency-domain is to con-

volute the spectrum of the window with that of

the actual input.

Figure 17 shows an FFT computed from an ideal

12-bit sinewave. The quality of the window used

for harmonic analysis is typically judged by its

highest side-lobe level. The Blackman-Harris

window used for testing the CS5014 and CS5016

has a maximum side-lobe level of -92 dB. Fig-

CS5012A, CS5014, CS5016

DS14F8

2-31

CS5012A CS5014 CS5016

DS14F9

CS5016 датащи(PDF) 25 Page - Cirrus Logic

CS5016 датащи(HTML) 25 Page - Cirrus Logic

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

датащи скачать

ссылки URL