4-/6-/8-Channel, 16-Bit,

Simultaneous-Sampling ADCs

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PACKAGE TYPE

PACKAGE CODE

DOCUMENT NO.

56 TQFN-EP

T5688+2

21-0135

Signal-to-Noise Ratio (SNR)

For a waveform perfectly reconstructed from digital

samples, SNR is the ratio of the full-scale analog input

(RMS value) to the RMS quantization error (residual

error). The ideal, theoretical minimum analog-to-digital

noise is caused by quantization noise error only and

results directly from the ADC’s resolution (N bits):

SNR = (6.02 x N + 1.76)dB

where N = 16 bits. In reality, there are other noise

sources besides quantization noise: thermal noise, ref-

erence noise, clock jitter, etc. SNR is computed by tak-

ing the ratio of the RMS signal to the RMS noise, which

includes all spectral components not including the fun-

damental, the first five harmonics, and the DC offset.

Signal-to-Noise Plus Distortion (SINAD)

SINAD is the ratio of the fundamental input frequency’s

RMS amplitude to the RMS equivalent of all the other

ADC output signals:

Effective Number of Bits (ENOB)

The ENOB indicates the global accuracy of an ADC at

a specific input frequency and sampling rate. An ideal

ADC’s error consists of quantization noise only. With an

input range equal to the full-scale range of the ADC,

calculate the ENOB as follows:

Total Harmonic Distortion (THD)

THD is the ratio of the RMS of the first five harmonics of

the input signal to the fundamental itself. This is

expressed as:

Spurious-Free Dynamic Range (SFDR)

SFDR is the ratio of the RMS amplitude of the funda-

mental (maximum signal component) to the RMS value

of the next-largest frequency component.

Aperture Delay

clock edge to the instant when an actual sample is

taken.

Aperture Jitter

aperture delay.

Channel-to-Channel Isolation

Channel-to-channel isolation indicates how well each

analog input is isolated from the other channels.

Channel-to-channel isolation is measured by applying

DC to channels 1 to 7, while a -0.4dBFS sine wave at

60Hz is applied to channel 0. A 10ksps FFT is taken for

channel 0 and channel 1. Channel-to-channel isolation

is expressed in dB as the power ratio of the two 60Hz

magnitudes.

Small-Signal Bandwidth

A small -20dBFS analog input signal is applied to an

ADC in a manner that ensures that the signal’s slew

rate does not limit the ADC’s performance. The input

frequency is then swept up to the point where the

amplitude of the digitized conversion result has

decreased 3dB.

Full-Power Bandwidth

A large -0.5dBFS analog input signal is applied to an

ADC, and the input frequency is swept up to the point

where the amplitude of the digitized conversion result

has decreased by 3dB. This point is defined as full-

power input bandwidth frequency.

Chip Information

PROCESS: BiCMOS

Package Information

For the latest package outline information and land patterns,

“-” in the package code indicates RoHS status only. Package

drawings may show a different suffix character, but the drawing

pertains to the package regardless of RoHS status.

THD

VVVV

V

=×

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20

2 2

3 2

4 2

5 2

1

log

ENOB

SINAD

=

602

.

.

SINAD dB

Signal

Noise

Distortion

RMS

()

log

(

=×

+

10

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