is provided as the upper comparator output voltage voutn since the upper voap and lower voan amplified voltages are close in value when the lower amplified voltage voan is sufficiently low its higher amplified voltage counterpart voap also becomes less than the lower reference voltage vclmplo as a result transistor q 79 fig3 turns on thereby diverting substantially all tail current provided by transistor q 0 from transistor q 77 this in turn prevents current flow through the current mirror circuitry formed by transistors q 39 q 29 and q 123 thereby causing transistor q 122 to be turned off and preventing either of the higher amplified voltage voap or the higher reference voltage vcmlphi to be buffered via transistors q 7 or q 117 respectively to the output voltage voutp hence the upper voltage comparator 106 p is turned off based upon the foregoing discussion it can be seen that the actual peak voltage levels at which the output voltage vout are determined by the substantially mutually exclusive upper voutp and lower voutn output voltage signals and are substantially equal to the higher vclmphi and lower vclmplo reference voltages it should also be readily understood that these reference voltages vclmphi vclmplo can be controlled e g programmed by appropriate design of the reference voltage source 108 circuitry fig2 c in conjunction with externally.