Clock speed trends
One popular parameter that often needs to reach its limit is the operating processor speed. More MHz equals more processing power (both performance and power dissipation). More processing power yields higher resolutions, more channels and fewer devices on a board. Given that silicon manufacturers need to productize a particular device for a wide audience, they need to test across a rigorous array of specifications; each device shipped to a customer must meet all of the data sheet specifications. Moreover, in order for a device to be successful in the market, it needs to be attractive to multiple applications, each with its own set of requirements. When putting together this device, it then needs to meet and exceed each and every one of these multi-application requirements.
That begs the question: What if this device had to meet your application requirements only?
shows the behavior of an internal memory test for a DSP at various voltages running at a high temperature. Figure 2
shows the same test, on the same DSP at room temperature.
As you can see, if this device is rated to run for a case temperature as high as 85ºC at, say, 1.2 V, the manufacturer must rate this device to run at 360 MHz at most.
However, if an application is designed such that the device will never operate above 25ºC (or less than 85ºC), you could theoretically run the same device at almost 500 MHz for this particular application.
Fig. 1: Voltage vs. MHz for a DSP at high temperature (85ºC)
Fig. 2: Voltage vs. MHz for same DSP at 25ºC (room temperature)
Another way to look at this data is that if the application environment called for an 85ºC operating temperature then increasing the voltage from 1.2 V to 1.4 V means this device could run at a speed higher than 700 MHz.
Lastly, if power is a consideration, one could run this application at 25ºC while dropping the voltage and keeping the clock speed constant in order to decrease the operating voltage.
Note that this data is for a specific test condition only. The important thing to remember here is that a particular application may only need a subset of the test conditions for a given device, hence giving an amount of flexibility with these parameters.
Tweaking the performance, power budget