LTC1604CG View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC1604CG' PDF : 20 Pages View PDF
LTC1604
APPLICATIONS INFORMATION
Intermodulation Distortion
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 fa and fb are applied
to the ADC input, nonlinearities in the ADC transfer func-
tion can create distortion products at the sum and differ-
ence frequencies of mfa ±nfb, where m and n = 0, 1, 2, 3,
0
fSAMPLE = 333kHz
–20
fIN1 = 29.3kHz
fIN2 = 32.4kHz
–40
–60
–80
–100
–120
–140
0
20 40 60 80 100 120 140 160
FREQUENCY (kHz)
1604 G06
Figure 21. Intermodulation Distortion Plot
etc. For example, the 2nd order IMD terms include
(fa – fb). If the two input sine waves are equal in magni-
tude, the value (in decibels) of the 2nd order IMD products
can be expressed by the following formula:
( ) IMD fa ± fb = 20Log Amplitude at (fa ± fb)
Amplitude at fa
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 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 amplitude of the reconstructed fundamental is
reduced by 3dB for a full-scale input signal.
The full-linear bandwidth is the input frequency at which
the S/(N + D) has dropped to 84dB (13.66 effective bits).
The LTC1604 has been designed to optimize input band-
width, allowing the ADC to undersample input signals with
frequencies above the converter’s Nyquist Frequency. The
noise floor stays very low at high frequencies; S/(N + D)
becomes dominated by distortion at frequencies far
beyond Nyquist.
18
Share Link: 
