The first was a method of controlling the edge speed:
The Analog Devices 21020 DSP chip has an external resistor for setting
edge speeds (all outputs). I've no idea how this works internally.
The other method reduced the production spread of edge speeds:
It seems that the parts that run faster also have faster edges.
The method involved
- an onboard oscillator that ran at a speed determined by the speed of
the device
- internal control on the output drivers to vary the edge speed
- a circuit that translated the oscillator speed to more or less drive
on the outputs
As a designer, it is obvious tpo me that there is a real need for
control over edge speeds.
I find it really exhausting to have to add hundreds of external
resistors, not to mention the additional costs, numbers of parts,
numbers of nodes to test etc etc.
I'd encourage the IC designers to be a bit more inventive.
Jon Keeble.
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