AD7273 Просмотр технического описания (PDF) - Analog Devices

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AD7273

3MSPS,10-/12-Bit ADCs in 8-Lead TSOT

Analog Devices 

PRELIMINARY TECHNICAL DATA

AD7273/AD7274

Preliminary Technical Data

TERMINOLOGY

Integral Nonlinearity (INL)

This is the maximum deviation from a straight line pass-

ing through the endpoints of the ADC transfer function.

For the AD7273/AD7274, the endpoints of the transfer

function are zero scale, a 1/2 LSB below the first code

transition, and full scale, a point 1/2 LSB above the last

code transition.

Differential Nonlinearity (DNL)

This is the difference between the measured and the

ideal 1 LSB change between any two adjacent codes in

the ADC.

Offset Error

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

000) to (00 . . . 001) from the ideal, i.e, AGND + 0.5 LSB.

Gain Error

This is the deviation of the last code transition (111 . . .

110) to (111 . . . 111) from the ideal, i.e, VREF –

1.5LSB after the offset error has been adjusted out.

Total Unadjusted Error (TUE)

This is a comprehensive specification which includes gain,

linearity and offset errors.

Track/Hold Acquisition Time

The Track/Hold acquisition time is the time required

for the output of the track/hold amplifier to reach its

final value, within ±0.5 LSB, after the end of

conversion. See Serial Interface section for more details.

Signal to Noise Ratio (SNR)

This is the measured ratio of signal to noise at the

output to the A/D converter. The signal is the rms value

of the sine wave input. Noise is the rms quantization

error within the Nyquist bandwitdh (fs/2). The rms

value of a sine wave is one half its peak to peak value

divided by √2 and the rms value for the quantization

noise is q/√12. The ratio is dependant on the number of

quantization levels in the digitization process; the more

levels, the smaller the quantization noise. For an ideal

N-bit converter, the SNR is defined as:

SNR = 6.02 N + 1.76 dB

Thus for a 12-bit converter this is 74 dB, for a 10-bit

converter it is 62 dB.

Practically, though, various error sources in the ADC

cause the measured SNR to be less than the theoretical

value. These errors occur due to integral and differential

nonlinearities, internal AC noise sources, etc.

Signal-to- (Noise + Distortion) Ratio (SINAD)

This is the measured ratio of signal to (noise +

distortion) at the output of the A/D converter. The

signal is the rms value of the sine wave and noise is the

rms sum of all nonfundamentals signals up to half the

sampling frequency (fs/2), including harmonics but

excluding dc.

Total Harmonic Distortion (THD)

Total harmonic distortion is the ratio of the rms sum of

harmonics to the fundamental. It is defined as:

THD (dB ) = 20 log

V

2

2

+ V32

+

V

2

4

+

V

2

5

+

V

2

6

V1

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

V3, V4, V5 and V6 are the rms amplitudes of the second

through the sixth harmonics.

Peak Harmonic or Spurious Noise (SFDR)

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 determined by the largest harmonic in the

spectrum, but for ADCs where the harmonics are buried

in the noise floor, it will be a noise peak.

Intermodulation Distortion (IMD)

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

distortion terms are those for which neither m nor n are

equal to zero. For example, the second order terms in-

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

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

The AD7273/AD7274 are tested using the CCIF standard

where two input frequencies are used (see fa and fb in the

specification page). In this case, the second order terms

are usually distanced in frequency from the original sine

waves while the third order terms are usually at a fre-

quency close to the input frequencies. As a result, the

second and third order terms are specified separately. 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 sum of the fundamentals expressed in dBs.

Power Supply Rejection Ratio (PSRR)

The power supply rejection ratio is defined as the ratio of the

power in the ADC output at full-scale frequency, f, to the

power of a 200 mV p-p sine wave applied to the ADC VDD

supply of frequency fs.

PSRR (dB) = 10 log (Pf/ Pfs)

Pf is the power at frequency f in the ADC output; Pfs is

the power at frequency fs coupled onto the ADC VDD

supply.

Aperture Delay

This is the measured interval between the leading edge of the

sampling clock and the point at which the ADC actually takes

the sample.

Aperture Jitter

This is the sample-to-sample variation in the effective point

in time at which the sample is taken.

–10–

REV. PrB

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