
19–16
Altera Corporation
Stratix GX Device Handbook, Volume 2
September 2004
Finite Impulse Response (FIR) Filters
Figure 19–9. TDM FIR Filter Implementation Note (1) (1)
details.
If the TDM factor is more than 2, then a multiply-accumulator needs to be
implemented. This multiply-accumulator can be implemented using the
soft logic outside the DSP block if all the multipliers of the DSP block are
needed. Alternatively, the multiply-accumulator may be implemented
inside the DSP block if all the multipliers of the DSP block are not needed.
The accumulator needs to be zeroed at the start of each new sample input.
The user also needs a way to store additional sample inputs in memory.
For example, consider a sample rate of r and TDM factor of 4. Then, the
Filter output
y(n)
Clock input
(1x clock)
1x clock
PLL
DQ
2x clock
x(n)
x
DSP block
Data input
RAM / ROM 0
RAM / ROM 1
RAM / ROM 2
RAM / ROM 3
Filter coefficients
D
Q
Accumulator
D
Q
D
Q
D
Q
D
Q
D
Q
D
Q
D
Q
Shift register