AD7457BRT-R2(Rev0) 데이터 시트보기 (PDF) - Analog Devices

부품명

상세내역

일치하는 목록

AD7457BRT-R2
(Rev.:Rev0)

Low Power, Pseudo Differential, 100 kSPS 12-Bit ADC in an 8-Lead SOT-23

Analog Devices 

AD7457

TERMINOLOGY

Signal to (Noise + Distortion) Ratio (SINAD)

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

output of the ADC. The signal is the rms amplitude of the

fundamental. Noise is the sum of all nonfundamental signals up

to half the sampling frequency (fS/2), excluding dc. The ratio is

dependent on the number of quantization levels in the digitiza-

tion process; the more levels, the smaller the quantization 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

Therefore, for a 12-bit converter, the SINAD is 74 dB.

Total Harmonic Distortion (THD)

The ratio of the rms sum of harmonics to the fundamental. For

the AD7457, it is defined as

THD(dB) = 20 log V22 + V32 + V42 + V52 + V62

V1

where:

V1 is the rms amplitude of the fundamental.

V2, V3, V4, V5, and V6 are the rms amplitudes of the second to the

sixth harmonics.

Peak Harmonic or Spurious Noise

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 specifica-

tion is determined by the largest harmonic in the spectrum, but,

for ADCs where the harmonics are buried in the noise floor, it is

a noise peak.

Intermodulation Distortion

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

fb, any active device with nonlinearities creates distortion

products at sum and difference frequencies of mfa ± nfb, where

m, n = 0, 1, 2, 3, and so on. Intermodulation distortion 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 (2fa + fb), (2fa − fb), (fa + 2fb) and

(fa − 2fb).

The AD7457 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 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

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 dB.

Aperture Delay

The amount of time from the leading edge of the sampling

clock until the ADC actually takes the sample.

Aperture Jitter

The sample-to-sample variation in the effective point in time at

which the actual sample is taken.

Full-Power Bandwidth

The full-power bandwidth of an ADC is that input frequency at

which the amplitude of the reconstructed fundamental is

reduced by 0.1 dB or 3 dB for a full-scale input.

Integral Nonlinearity (INL)

The maximum deviation from a straight line passing through

the endpoints of the ADC transfer function.

Differential Nonlinearity (DNL)

The difference between the measured and the ideal 1 LSB

change between any two adjacent codes in the ADC.

Offset Error

The deviation of the first code transition (000...000 to 000...001)

from the ideal (that is, AGND + 1 LSB).

Gain Error

The deviation of the last code transition (111...110 to 111...111)

from the ideal (that is, VREF − 1 LSB), after the offset error has

been adjusted out.

Track-and-Hold Acquisition Time

The minimum time required for the track-and-hold amplifier to

remain in track mode for its output to reach and settle to within

0.5 LSB of the applied input signal.

Power Supply Rejection Ratio (PSRR)

The ratio of the power in the ADC output at full-scale

frequency, f, to the power of a 100 mV p-p sine wave applied to

the ADC VDD supply of frequency fs. The frequency of this

input varies from 1 kHz to 1 MHz.

PSRR (dB) = 10 log (Pf Pfs)

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

power at frequency fs in the ADC output.

Rev. 0 | Page 8 of 20

Share Link: