1.17. Variable Precision DSP Block
The Stratix® 10 DSP blocks are based upon the Variable Precision DSP Architecture used in Altera’s previous generation devices. They feature hard fixed point and IEEE 754 compliant floating point capability.
The DSP blocks can be configured to support signal processing with precision ranging from 18x19 up to 54x54. A pipeline register has been added to increase the maximum operating frequency of the DSP block and reduce power consumption.
Each DSP block can be independently configured at compile time as either dual 18x19 or a single 27x27 multiply accumulate. With a dedicated 64 bit cascade bus, multiple variable precision DSP blocks can be cascaded to implement even higher precision DSP functions efficiently.
In floating point mode, each DSP block provides one single precision floating point multiplier and adder. Floating point additions, multiplications, mult-adds and mult-accumulates are supported.
The following table shows how different precisions are accommodated within a DSP block, or by utilizing multiple blocks.
Multiplier Size |
DSP Block Resources |
Expected Usage |
---|---|---|
18x19 bits |
1/2 of Variable Precision DSP Block |
Medium precision fixed point |
27x27 bits |
1 Variable Precision DSP Block |
High precision fixed point |
19x36 bits |
1 Variable Precision DSP Block with external adder |
Fixed point FFTs |
36x36 bits |
2 Variable Precision DSP Blocks with external adder |
Very high precision fixed point |
54x54 bits |
4 Variable Precision DSP Blocks with external adder |
Double Precision floating point |
Single Precision floating point | 1 Single Precision floating point adder, 1 Single Precision floating point multiplier | Floating point |
Complex multiplication is very common in DSP algorithms. One of the most popular applications of complex multipliers is the FFT algorithm. This algorithm has the characteristic of increasing precision requirements on only one side of the multiplier. The Variable Precision DSP block supports the FFT algorithm with proportional increase in DSP resources as the precision grows.
Complex Multiplier Size |
DSP Block Resources |
FFT Usage |
---|---|---|
18x19 bits |
2 Variable Precision DSP Blocks |
Resource optimized FFT |
27x27 bits |
4 Variable Precision DSP Blocks |
Highest precision FFT |
For FFT applications with high dynamic range requirements, the Altera FFT IP Core offers an option of single precision floating point implementation with resource usage and performance similar to high precision fixed point implementations.
Other features of the DSP block include:
- Hard 18 bit and 25 bit pre-adders
- Hard floating point multipliers and adders
- 64 bit dual accumulator (for separate I, Q product accumulations)
- Cascaded output adder chains for 18 and 27 bit FIR filters
- Embedded coefficient registers for 18 and 27 bit coefficients
- Fully independent multiplier outputs
- Inferability using HDL templates supplied by the Quartus® Prime software for most modes
The Variable Precision DSP block is ideal to support the growing trend towards higher bit precision in high performance DSP applications. At the same time, it can efficiently support the many existing 18 bit DSP applications, such as high definition video processing and remote radio heads. With the Variable Precision DSP block architecture and hard floating point multipliers and adders, Stratix® 10 devices can efficiently support many different precision levels up to and including floating point implementations. This flexibility can result in increased system performance, reduced power consumption, and reduce architecture constraints on system algorithm designers.