Simulation of Voltage Scaling for Dynamic Power Reduction

Some background info:
In a previous blog, I introduced:

• DVFS (Dynamic Voltage and Frequency Scaling), a technique used for Dynamic Power Reduction.
• RVM (Real Valued Modeling) for efficient simulation of mixed signal SoC with very high speed and efficiency using Cadence DMS (Digital Mixed Signal) offerings. See “Part1: Using wreals to simulate Frequency Scaling for Dynamic Power Reduction” for details

In that blog, I addressed Frequency Scaling using wreals modeling. Now, allow me to focus on how to simulate Voltage Scaling also using RVM. The full topic will be covered in a series of blogs. This is a first one of a series…

Controlled Voltage source:
Here’s an example of using advanced techniques in the testbench to create a controlled voltage source - in this case using constrained random generation of real numbers in Specman. A noisy voltage-source, such as a battery supply that varies over time and also drifts with temperature and use can be created as shown in this blog. The battery-voltage is supplied to an LDO that serves to regulate the noisy voltage so that it can be used for precise voltage variations used in voltage scaling of design elements.

But first, let’s look at the voltage generation the TB. Example below shows how Specman gets access to the DUT and other HDL elements in the Verification Env using hdl_paths() and port-maps. There ere two possible scenarios:

1. Use externally supplied constraints for min/max voltage values
2. Specify min/max voltage constraints form within the Specman env.

In either case, voltage values are created within the supplied constraints using a rdist_uniform() routine to generate real numbers.

rdist_uniform(from : real, to :real): real
Returns a random real number using uniform distribution in the range from to to.

This feature does require the use of Intelligen solver which is invoked by a switch in irun: -snset "config gen -default_generator=IntelliGen"

The following constraints were used in this example, resulting in the voltage source – see waveform. The rate of voltage generation (samples per sec) can also be configured from the verification env.

In this blog, I covered how Voltages sources can be generated from the verification env. In the next blog I will cover how voltages get regulated with precision and then supplied to the various voltage islands on the chip. In the continuing series of blogs, I will then cover how nominal voltages are specified and controlled and how voltage scaling occurs with and modulated in a closed-loop env with feedback form individual design entities against targeted performance. I will also cover checking and coverage and error detection, including the effects of voltage overshoot/undershoot on system

Stay tuned for more…
Neyaz Khan