We've talked about lots of different integrated solutions to various design needs. We've had blogs about analog front ends, power management devices, hearing aids, factory automation, and health-related devices.
Assuming you've followed the intent of these blogs and had custom integrated analog ICs made to your exacting specifications, you now have an IC on your circuit board that performs amazing technological tasks in a tiny amount of board space. Unless it doesn't.
Then what? Warm up the scope and the coffee pot and start troubleshooting the board. Sadly, because you put all that functionality inside, you can't tell where the signal gets mucked up or where the power supply voltages get all weird. Here's an example.
If you used a device like this and the MCU wasn't working right, maybe the internal bias supply (or similar LDO) was not supplying the right voltage. Can you tell? Perhaps adding one pin to bring that voltage out for test purposes would have been a good idea. Here's another example.
This is a discrete IC version of a portion of a software-defined radio. Assuming you integrated the Johnson counter, the Tayloe detector, and the op-amp circuitry into one piece of silicon, consider the utility of adding test points (brought out on pins) for the counter and detector outputs. That would greatly simplify troubleshooting.
Here's a block diagram of sorts from one of Maxim Integrated's devices. (Maxim is the sponsor of this site.) This one could be part of a data acquisition system used in some factory automation equipment. As before, if you plan ahead and bring out test points from the interconnects between each stage, life will be so much easier once production starts.
Here's one more simple example of the right way to do this. In this case, the device is indeed pretty simple. As integrated analog goes, this barely qualifies, since it's simply an instrumentation amplifier.
At first glance, it looks quite conventional, but there are two additional signals brought out — the connections to the input stage op-amps. This allows you to see what is going on at these points, and it can supply very useful information.
What complex integrated devices have you used? Did you wish you had access to additional signals or test points?
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