AD7864AS-3 datasheet(7/19 Pages) AD

Numer części	AD7864AS-3

Szczegółowy opis	4-Channel, Simultaneous Sampling, High Speed, 12-Bit ADC

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Producent	AD [Analog Devices]

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AD7864

–7–

REV. A

TERMINOLOGY

Signal to (Noise + Distortion) Ratio

This is the measured ratio of signal to (noise + distortion) at the

output of the A/D converter. The signal is the rms amplitude of

the fundamental. Noise is the rms sum of all nonfundamental

signals up to half the sampling frequency (fS/2), excluding dc.

The ratio is dependent upon the number of quantization levels

in the digitization process; the more levels, the smaller the quan-

tization noise. The theoretical signal to (noise + distortion) ratio

for an ideal N-bit converter with a sine wave input is given by:

Signal to (Noise + Distortion) = (6.02 N + 1.76) dB

Thus for a 12-bit converter, this is 74 dB.

Total Harmonic Distortion

Total harmonic distortion (THD) is the ratio of the rms sum of

harmonics to the fundamental. For the AD7864 it is defined as:

THD dB

()=20 log V2

2

+V

3

2

+V

4

2

+V

5

2

+V

6

2

V1

where V1 is the rms amplitude of the fundamental and V2, V3,

V4 and V5 are the rms amplitudes of the second through the fifth

harmonics.

Peak Harmonic or Spurious Noise

Peak harmonic or spurious noise is defined as the ratio of the

rms value of the next largest component in the ADC output

spectrum (up to fS/2 and excluding dc) to the rms value of the

fundamental. Normally, the value of this specification is deter-

mined by the largest harmonic in the spectrum, but for parts

where the harmonics are buried in the noise floor, it will be a

noise peak.

Intermodulation Distortion

With inputs consisting of sine waves at two frequencies, fa and

fb, any active device with nonlinearities will create distortion

products at sum and difference frequencies of mfa

± nfb where

m, n = 0, 1, 2, 3, etc. Intermodulation terms are those for which

neither m nor n are equal to zero. For example, the second

order terms include (fa + fb) and (fa – fb), while the third order

terms include (2 fa + fb), (2 fa – fb), (fa + 2 fb) and (fa – 2 fb).

The AD7864 is tested using the CCIF standard, where two

input frequencies near the top end of the input bandwidth are

used. In this case, the second and third order terms are of differ-

ent significance. The second order terms are usually distanced

in frequency from the original sine waves, while the third order

terms are usually at a frequency close to the input frequencies.

As a result, the second and third order terms are specified sepa-

rately. The calculation of the intermodulation distortion is as

per the THD specification where it is the ratio of the rms sum of

the individual distortion products to the rms amplitude of the

fundamental expressed in dBs.

Channel-to-Channel Isolation

Channel-to-Channel isolation is a measure of the level of

crosstalk between channels. It is measured by applying a full-

scale 50 kHz sine wave signal to all nonselected input channels

and determining how much that signal is attenuated in the

selected channel. The figure given is the worst case across all four

channels.

Relative Accuracy

Relative accuracy or endpoint nonlinearity is the maximum

deviation from a straight line passing through the endpoints of

the ADC transfer function.

Differential Nonlinearity

This is the difference between the measured and the ideal

1 LSB change between any two adjacent codes in the ADC.

Positive Full-Scale Error

This is the deviation of the last code transition (01 . . . 110 to

01 . . . 111) from the ideal 4

× VREF – 3/2 LSB (AD7864-1

±10 V), 2 × VREF – 3/2 LSB (AD7864-1 ±5 V range) or VREF

– 3/2 LSB (AD7864-3,

±2.5 V range), after the Bipolar Offset

Error has been adjusted out.

Positive Full-Scale Error (AD7864-2, 0 V to 2.5 V and 0 V to

5 V)

This is the deviation of the last code transition (11 . . . 110 to

11 . . . 111) from the ideal 2

× VREF – 3/2 LSB (AD7864-2 0 V

to 5 V range), or VREF – 3/2 LSB (AD7864-2 0 V to 2.5 V

range), after the Unipolar Offset Error has been adjusted out.

Bipolar Zero Error (AD7864-1,

10/ 5 V, AD7864-3 ,

2.5 V)

This is the deviation of the midscale transition (all 0s to all 1s)

from the ideal AGND – 1/2 LSB.

Unipolar Offset Error (AD7864-2, 0 V to 2.5 V and 0 V to 5 V)

This is the deviation of the first code transition (00 . . . 000 to

00 . . . 001) from the ideal AGND + 1/2 LSB.

Negative Full-Scale Error (AD7864-1,

10/ 5 V, AD7864-3,

2.5 V)

This is the deviation of the first code transition (10 . . . 000 to

10 . . . 001) from the ideal –4

× VREF + 1/2 LSB (AD7864-1

±10 V), –2 × VREF + 1/2 LSB (AD7864-1 ±5 V range) or

–VREF + 1/2 LSB (AD7864-3,

±2.5 V range), after Bipolar

Zero Error has been adjusted out.

Track/Hold Acquisition Time

Track/Hold acquisition time is the time required for the out-

put of the track/hold amplifier to reach its final value, within

±1/2 LSB, after the end of conversion (the point at which the

track/hold returns to track mode). It also applies to situations

where there is a step input change on the input voltage applied

to the selected VINXA/VINXB input of the AD7864. It means that

the user must wait for the duration of the track/hold acquisition

time after the end of conversion or after a step input change to

VINXA/VINXB before starting another conversion, to ensure that

the part operates to specification.

Podobny numer części - AD7864AS-3

Producent	Numer części	Arkusz danych	Szczegółowy opis
Analog Devices	AD7864ASZ-1	673Kb / 29P	4-Channel, Simultaneous Sampling, High Speed, 12-Bit ADC
	AD7864ASZ-12	760Kb / 28P	4-Channel, Simultaneous Sampling, High Speed, 12-Bit ADC REV. D
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	AD7864ASZ-1REEL2	760Kb / 28P	4-Channel, Simultaneous Sampling, High Speed, 12-Bit ADC REV. D
	AD7864ASZ-2	673Kb / 29P	4-Channel, Simultaneous Sampling, High Speed, 12-Bit ADC

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Producent	Numer części	Arkusz danych	Szczegółowy opis
Analog Devices	AD7864	760Kb / 28P	4-Channel, Simultaneous Sampling, High Speed, 12-Bit ADC REV. D
	AD7864	673Kb / 29P	4-Channel, Simultaneous Sampling, High Speed, 12-Bit ADC
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