ADC

ADC

ADC

ADC

ADC

AS1419

AS1419A

AS1419 & AS1419A

Rev. 1.5 08/09

Austin Semiconductor, Inc. reserves the right to change products or specifications without notice.

9

Austin Semiconductor, Inc.

Signal-to-Noise Ratio

The signal-to-noise plus distortion ratio [S/(N + D)] is the

ratio between the RMS amplitude of the fundamental input

frequency to the RMS amplitude of all other frequency

components at the A/D output. The output is band limited to

frequencies from above DC and below half the sampling

frequency. Figure 2 shows a typical spectral content with a

800kHz sampling rate and a 100kHz input. The dynamic

performance is excellent for input frequencies up to and

beyond the Nyquist limit of 400kHz.

Effective Number of Bits

The effective number of bits (ENOBs) is a measurement of

the resolution of an ADC and is directly related to the S/(N + D)

by the equation:

N = [S/(N + D) – 1.76]/6.02

where N is the effective number of bits of resolution and

S/(N + D) is expressed in dB. At the maximum sampling rate of

800kHz, the AS1419 maintains near ideal ENOBs up to the

Nyquist input frequency of 400kHz (refer to Figure 3).

(Noise+Distortion) vs. Input Frequency

Total Harmonic Distortion

Total harmonic distortion (THD) is the ratio of the RMS

sum of all harmonics of the input signal to the fundamental

itself. The out-of-band harmonics alias into the frequency band

between DC and half the sampling frequency. THD is expressed

as:

where V1 is the RMS amplitude of the fundamental frequency

and V2 through Vn are the amplitudes of the second through

nth harmonics. THD vs Input Frequency is shown in Figure 4.

The AS1419 has good distortion performance up to the Nyquist

frequency and beyond.

Plot