Linear Technology DC1190A-A - LTC2366: 12-bit, 3Msps SAR ADC (req DC590B for DC apps, DC890B for AC apps) DC1190A-A DC1190A-A Fiche De Données
Codes de produits
DC1190A-A
LTC2365/LTC2366
13
23656fb
applications inForMation
Figure 9b. LTC2366 Intermodulation Distortion Plot
Intermodulation Distortion
If the ADC input signal consists of more than one spectral
If the ADC input signal consists of more than one spectral
component, the ADC transfer function nonlinearity can
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
If two pure sine waves of frequencies f
a
and f
b
are applied
to the ADC input, nonlinearities in the ADC transfer function
can create distortion products at the sum and difference
frequencies of mf
a
± nf
b
, where m and n = 0, 1, 2, 3, etc.
For example, the 2nd order IMD terms include (f
a
± f
b
).
If the two input sine waves are equal in magnitude, the
value (in decibels) of the 2nd order IMD products can be
expressed by the following formula:
IMD(f
a
± f
b
)
= 20log
Amplitude at (f
a
± f
b
)
Amplitude at f
a
The LTC2365/LTC2366 have good IMD as shown in
Figure 9a and Figure 9b, respectively.
Peak Harmonic or Spurious Noise
The peak harmonic or spurious noise is the largest spectral
The peak harmonic or spurious noise is the largest spectral
component excluding the input signal and DC. This value
is expressed in decibels 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 full-power bandwidth is that input frequency at which
the amplitude of reconstructed fundamental is reduced by
3dB for full-scale input signal.
The full-linear bandwidth is the input frequency at which
The full-linear bandwidth is the input frequency at which
the SINAD has dropped to 68dB (11 effective bits). The
LTC2365/LTC2366 have been designed to optimize input
bandwidth, allowing the ADC to undersample input sig-
nals with frequencies above the converter’s Nyquist Fre-
quency. The noise floor stays very low at high frequencies;
SINAD becomes dominated by distortion at frequencies
far beyond Nyquist.
Figure 9a. LTC2365 Intermodulation Distortion Plot
INPUT FREQUENCY (kHz)
0
–140
MAGNITUDE (dB)
–120
–80
–60
–40
0
50
250
350
23656 F09a
–100
–20
200
450 500
100 150
300
400
V
DD
= 3V
f
SMPL
= 1Msps
f
b
= 396kHz
f
b
= 424kHz
IMD = –73.5dB
INPUT FREQUENCY (kHz)
0
0
–20
–40
–60
–80
–100
–120
–140
750
1250
23656 F09b
250
500
1000
1500
MAGNITUE (dB)
V
DD
= 3V
f
SMPL
= 3Msps
f
a
= 935kHz
f
b
= 1.045kHz
IMD = –71.5dB