ISL5239 Datasheet, PDF (9/31 Pages) Intersil Corporation – Pre-Distortion Linearizer

ISL5239
The IF converter frequency response is as shown in
Figure 7, with the folding effect shown in Figure 7A for the
x2, Fs/4 upconverter case.
IFC FILTER RESPONSE (x2 MODE)
0
-20
-40
-60
-80
-100
-120
-140
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
NORMALIZED FREQUENCY (NYQUIST=1)
FIGURE 7. x2, IFC FREQUENCY RESPONSE
IFC FILTER RESPONSE (x2 MODE, WITH FOLDING)
0
-20
-40
-60
-80
-100
-120
-140
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
NORMALIZED FREQUENCY (NYQUIST=1)
FIGURE 7A. x2, IFC FREQUENCY RESP. WITH FOLDING
Complex
The complex operating mode simply shifts the complex
baseband signal up by Fs/4 without any filtering or real
conversion. The operation of the IF converter in this mode is
shown in Figure 8.
Correction Filter (CF)
To compensate for imperfections in the analog filtering which
takes place after D/A conversion, the correction filter
provides an independent 13-tap FIR filter on each channel.
These filters may be programmed to remove differential
group delay and ripple characteristics of external analog
circuits including sin(x)/x correction and frequency response
imbalance between the I and Q channels using either
amplitude or group delay. This allows for correction of the
two physically separate I and Q analog response paths from
the DAC’s through the quadrature up-converter. It also
provides correction of the bandpass response when
operating in a complex frequency shifted IF mode. There are
two possible correction filter modes.
Real 2X
When the IF Converter is set to generate 2x sampled real
data, the Correction Filter must be reconfigured to process
this data correctly. In this mode it effectively provides one 13-
tap block-mode filter when the coefficients for the two filters
are programmed identically.
BYPASS
I
2
Q
2
Z^-1
FROM
IFC
I/Q FIRs
Z^-1
2I
2
Q
FIGURE 9. CORRECTION FILTER IN REAL 2X MODE
Complex or Real 1x
When configured for operation in the complex mode, one 13-
tap filter is provided for each the I and Q channels. In Real 1x
mode, the Q channel is not used.
I
Q
FROM
IFC
BYPASS
I-CHAN
I
FIR
Q-CHAN
Q
FIR
FIGURE 10. CORRECTION FILTER IN COMPLEX MODE
BYPASS
I
I
Q
Q
FROM
PD
e^j(pi/2)(n)
FIGURE 8. IF CONVERTER IN COMPLEX MODE OPERATION
Output Data Conditioner (ODC)
The Output Data Conditioner can apply I/Q balance
corrections, DC offset corrections and output format
conversions.
To compensate for gain/phase imperfections in external
analog modulation circuits which can result in poor image
rejection and reduced dynamic range, the ODC provides an
I/Q balance corrector. The I/Q balance corrector provides
four coefficients to control the magnitude of the direct and
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