ADC
AS1419
AS1419A
Austin Semiconductor, Inc.
Signal-to-Noise Ratio
Total Harmonic Distortion
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.
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:
Effective Number of Bits
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.
TheAS1419 has good distortion performance up to the Nyquist
frequency and beyond.
The effective number of bits (ENOBs) is a measurement of
the resolution of anADC 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).
FIGURE 4: Distortion vs. Input Frequency
FIGURE 3: Effective Bits and Signal/
(Noise+Distortion) vs. Input Frequency
FIGURE 5: Intermodulation Distortion
Plot
Austin Semiconductor, Inc. reserves the right to change products or specifications without notice.
AS1419 & AS1419A
Rev. 0.1 1/04
9
MICROSS [ MICROSS COMPONENTS ]
