A protection circuit for a signal processor, a method of operating the protection circuit, and a method of forming the protection circuit. In one example, the protection circuit is couplable to a signal port and a first power bus for the signal processor. The protection circuit includes a first diode string couplable across the signal port and the first power bus. The first diode string includes a first diode and a second diode coupled in series in a same polarity sense. The protection circuit also includes a third diode coupled in parallel with one of the first diode and the second diode in an opposite polarity sense.