Figure 12. T/H Aperture Timing
MAX1446
ground pins could share the same ground plane if the
ground plane is sufficiently isolated from any noisy, dig-
ital systems ground plane (e.g., downstream output
buffer or DSP ground plane). Route high-speed digital
signal traces away from sensitive analog traces. Keep
all signal lines short and free of 90° turns.
Static Parameter Definitions
Integral Nonlinearity
Integral nonlinearity (INL) is the deviation of the values
on an actual transfer function from a straight line. This
straight line can be either a best-straight-line fit or a line
drawn between the endpoints of the transfer function
once offset and gain errors have been nullified. The
MAX1446’s static linearity parameters are measured
using the best-straight-line fit method.
Differential Nonlinearity
Differential nonlinearity (DNL) is the difference between
an actual step width and the ideal value of 1LSB. A
DNL error specification of less than 1LSB guarantees
no missing codes and a monotonic transfer function.
Dynamic Parameter Definitions
Aperture Jitter
Figure 12 depicts the aperture jitter (t
AJ
), which is the
sample-to-sample variation in the aperture delay.
Aperture Delay
Aperture delay (t
AD
) is the time defined between the
falling edge of the sampling clock and the instant when
an actual sample is taken (Figure 12).
Signal-to-Noise Ratio (SNR)
For a waveform perfectly reconstructed from digital
samples, the theoretical maximum SNR is the ratio of
the full-scale analog input (rms value) to the rms quanti-
zation error (residual error). The ideal, theoretical mini-
mum A/D noise is caused by quantization error only
and results directly from the ADC’s resolution (N bits):
SNR
(MAX)
= 6.02 x N + 1.76
In reality, there are other noise sources besides quanti-
zation noise: thermal noise, reference noise, clock jitter,
etc. SNR is computed by taking the ratio of the rms sig-
nal to the rms noise, which includes all spectral compo-
nents minus the fundamental, the first five harmonics,
and the DC offset.
Signal-to-Noise Plus Distortion (SINAD)
SINAD is computed by taking the ratio of the rms signal
to all spectral components minus the fundamental and
the DC offset.
Effective Number of Bits (ENOB)
ENOB specifies the dynamic performance of an ADC at
a specific input frequency and sampling rate. An ideal
ADC’s error consists of quantization noise only. ENOB
is computed from:
Total Harmonic Distortion (THD)
THD is typically the ratio of the rms sum of the input
signal’s first four harmonics to the fundamental itself.
This is expressed as:
where V
1
is the fundamental amplitude, and V
2
through
V
5
are the amplitudes of the 2nd- through 5th-order
harmonics.
Spurious-Free Dynamic Range (SFDR)
SFDR is the ratio expressed in decibels of the rms
amplitude of the fundamental (maximum signal compo-
nent) to the rms value of the next largest spurious com-
ponent, excluding DC offset.
Intermodulation Distortion (IMD)
The two-tone IMD is the ratio expressed in decibels of
either input tone to the worst 3rd-order (or higher) inter-
modulation products. The individual input tone levels
are at -6.5dB full scale.
.
