LTC1196-1BC Linear Technology, LTC1196-1BC Datasheet - Page 22

• Manufacturer Part Number: LTC1196-1BC
• Description: 8-Bit/ SO-8/ 1MSPS ADCs with Auto-Shutdown Options
• Manufacturer: Linear Technology

LTC1196/LTC1198
A
rate of 1.2MHz with a 5V supply the LTC1196 maintains
above 7.5 ENOBs at 400kHz input frequency. Above 500kHz
the ENOBs gradually decline, as shown in Figure 11, due
to increasing second harmonic distortion. The noise floor
remains low.
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 of the sampling frequency. THD
is defined as:
where V
quency and V
second through the N
fication in the Dynamic Accuracy table includes the 2nd
through 5th harmonics. With a 100kHz input signal, the
LTC1196/LTC1198 have typical THD of 50dB and 49dB
with V
Intermodulation Distortion
If the ADC input signal consists of more than one spectral
component, the ADC transfer function nonlinearity can
22
PPLICATI
THD 20log
Figure 11. Effective Bits and S/(N + D) vs Input Frequency
CC
1
= 5V and V
is the RMS amplitude of the fundamental fre-
8
7
6
5
4
3
2
1
0
1k
2
O
T
through V
A
V
= 25°C
f
f
SMPL
SMPL
U
2
2
CC
th
f
SMPL
S
f
INPUT FREQUENCY (Hz)
SMPL
= 383kHz (LTC1196)
= 287kHz (LTC1198)
harmonics. The typical THD speci-
= 3V, respectively.
V
10k
V
3
2
= 750kHz (LTC1198)
REF
I FOR ATIO
= 1MHz (LTC1196)
U
N
= V
V
V
V
REF
1
are the amplitudes of the
CC
4
2
= V
= 2.7V
CC
100k
= 5V
W
V
N
1196/98 G24
2
1M
50
44
U
produce intermodulation distortion (IMD) in addition to
THD. IMD is the change in one sinusoidal input caused by
the presence of another sinusoidal input at a different
frequency.
If two pure sine waves of frequencies f
to the ADC input, nonlinearities in the ADC transfer func-
tion can create distortion products at sum and difference
frequencies of mf
For example, the 2nd order IMD terms include (f
(f
(2f
waves are equal in magnitudes, the value (in dB) of the 2nd
order IMD products can be expressed by the following
formula:
For input frequencies of 499kHz and 502kHz, the IMD of
the LTC1196/LTC1198 is 51dB with a 5V supply.
Peak Harmonic or Spurious Noise
The peak harmonic or spurious noise is the largest spec-
tral component excluding the input signal and DC. This
value is expressed in dBs relative to the RMS value of a full-
scale input signal.
Full-Power and Full-Linear Bandwidth
The full-power bandwidth is that input frequency at which
the amplitude of the reconstructed fundamental is re-
duced by 3dB for a full-scale input.
The full-linear bandwidth is the input frequency at which
the effective bits rating of the ADC falls to 7 bits. Beyond
this frequency, distortion of the sampled input signal
increases. The LTC1196/LTC1198 have been designed to
optimize input bandwidth, allowing the ADCs to
undersample input signals with frequencies above the
converters’ Nyquist Frequency.
a
a
IMD f
– f
– f
b
b
) while 3rd order IMD terms include (2f
), (f
a
a
f
b
+ 2f
20log
a
b
), and (f
nf
b
, where m and n = 0, 1, 2, 3, etc.
a
mplitude f
amplitude at f
a
– 2f
b
). If the two input sine
a
a
and f
f
a
b
b
are applied
a
+ f
a
b
+ f
) and
b
),