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36.12.3 IIR Applications
Among other things, the IIR is used in timing recovery and interpolating Þlter.
36.13 Modulation (MOD)ÐReal Sin, Real Cos,
Complex X, and Real/Complex Y
Using the values provided in the parameter packet, the MOD implements a basic modulator
function, shown in Figure 36-24, with a modulation table composed of {cos wnT, sin wnT}
pairs, complex input samples, and real outputs. The input data is in a circular buffer with
size (M+1) and the output data is in a circular buffer with size (N+1).
Real Y n ( )
Image Y n ( )
36.13.1 Modulation Table, Input, and Output Buffers
The modulation table consists of 16-bit cosine and sine pairs that occupy (K+1) bytes in
memory. The input sample buffer is a circular buffer containing (M+1) bytes. Each sample
is a pair of 16-bit entries (real and imaginary components) and the next sample is stored in
the address that follows the previous sample. The output buffer is a circular buffer that
contain (N+1) bytes and the next output is stored in the address that follows the previous
output. The output buffer can be real or complex, depending on FD[X]. See Table 36-19.
Table 36-19. MOD Table, Input, and Output Buffers
Modulation Table
sin q
1
cos q
1
sin q
2
cos q
2
*
*
sin q
n
cos q
n
MOTOROLA
X(n)
{Complex}
cos wnT, sin wnT
{Real}
{
}
Real X n ( )
{
}
´
cos
=
{
}
Real X n ( )
{
}
´
sin
=
Figure 36-24. MOD Function
Input Samples
*
*
imaginary{x(n-k+1)}
real{x(n-k+1)}
*
*
imaginary{x(n-2)}
real{x(n-2)}
imaginary{x(n-1)}
Chapter 36. Digital Signal Processing
Part V. The Communications Processor Module
Y(n)
{Real or Complex}
wnT
Image X n ( )
{
}
´
Ð
sin
wnT
Image X n ( )
{
}
´
+
cos
Complex Output, FD[X]=1
*
*
imaginary{Y(n-k+1)}
real{Y(n-k+1)}
*
*
imaginary{Y(n-2)}
real{Y(n-2)}
imaginary{Y(n-1)}
wnT
wnT
Real Output, FD[X]=0
*
*
real{Y(n-k+1)}
*
*
real{Y(n-2)}
real{Y(n-1)
real{Y(n)}
36-21
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