Intel 8253 - Page 226

Solution
A 100-mV
pp
sinusoidal signal is applied to an ideal 12-bit A/D converter for which
V
ref
= 5 V. Find the SNR of the digitized output signal.
First, we use to find the maximum SNR if a full-scale sinusoidal wave-form of 2.5 V
were applied to the input.
±
Idealized SNR versus sinusoidal input signal amplitude for a 10-bit A/D converter. The
0-dB input signal amplitude corresponds to a peak-to-peak voltage equaling V
ref
.
However, since the input is only a 100-mV sinusoidal waveform that is 28 dB below
full scale, the SNR of the digitized output is
±
dB7476.11202.6dB76.1N02.6SNR
max
=+×=+=
dB
46
28
74
SNR
=−=
Numerical Examples [1]
Example 1.








=








=








=
N
LSB
ref
Q
in
2
2
3
log20
12/V
)22/(V
log20
)rms(V
)rms(V
log20SNR
SNR
(dB)
60
50
40
30
20
10
-60
-50 -40 -30
-20 -10 0
0
V
in
(dB)
V
pp
=V
ref
Best possible SNR
Best real SNR