Altera offers a patent-pending implementation of soft multipliers that uses TriMatrix™ memory blocks in Stratix™ II devices for applications that require a very large number of multipliers, such as third-generation (3G) basestations and image-processing applications. These soft multipliers can be configured for various latency, memory, and multiplier sizes, which enable designers to customize the implementation of their digital signal processing (DSP) systems to match the requirements of a particular DSP application.
The soft multiplier is based on a look-up table (LUT) implementation of the multiplication operation, where the LUT is implemented in memory. Stratix II devices feature versatile DSP blocks that support up to 384 high-performance 18x18 hardware multipliers. Designers can also implement soft multipliers using M4K and M512 memory blocks in Stratix II devices.
The soft multipliers can be configured in various data sizes and can provide up to 962 multipliers when implemented in the 16x16 mode. Combined with the 384 multipliers available in the DSP blocks, Stratix II devices provide an astounding 1,346 multipliers that are ideal for implementing distributed arithmetic computations, as well as multi-channel applications such as echo cancellation, multi-user detection, and beam-forming. Together with the DSP blocks and soft multipliers, Stratix II devices provide highly effective multiplier bandwidth.
Figure 1 shows a finite impulse response (FIR) filter implementation using the M4K memory blocks in Stratix II devices. A similar implementation is also possible using the M512 blocks in Stratix II devices.
Figure 1. Soft Multiplier Implementation of a FIR Filter in M4K Blocks
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Table 1. Number of Soft Multipliers Using M512 & M4K Blocks (1), (2) | |||
| Device | Number of Soft Multipliers | ||
|---|---|---|---|
| Using M4K Blocks |
Using M512 Blocks |
Total | |
| EP2S15 | 68 | 32 | 100 |
| EP2S30 | 126 | 63 | 189 |
| EP2S60 | 223 | 102 | 325 |
| EP2S90 | 357 | 152 | 509 |
| EP2S130 | 532 | 218 | 750 |
| EP2S180 | 672 | 290 | 962 |
Soft multipliers can be implemented in Stratix II devices using their M4K and the M512 memory blocks. Table 1 summarizes the number of 16x16 soft multipliers available in Stratix II devices.
Notes:
- Numbers are based on 16x16 multipliers using sum of multiplications mode
- Sum of coefficients is assumed not to exceed 18 bits
Designers can use soft multipliers implemented in unused TriMatrix memory to fit a design in a smaller device. This means that designers can use a combination of DSP blocks and soft multipliers to optimize their design for performance, flexibility, and lower cost.
