positive input of the bs follower amplifier 66 is connected to the positive input of the a d comparator amplifier 40 the output of the bs follower amplifier 66 is connected at the junction of the two zener diodes 76 and 78 these two zener diodes 76 and 78 set the operating points for the plus and minus supply follower transistors 84 and 86 respectively the transistors 84 and 86 are set up so as to provide a bootstrap power supply via leads 88 and 90 to the a d comparator amplifier 40 thus the bootstrap power supply 14 provides a power supply that bootstraps on tracks the a d amplifier comparator 40 inputs so it never sees a common mode input signal this makes it feasible to use a lower grade amplifier than heretofore believed possible for the a d comparator amplifier 40 when the a d comparator amplifier 40 is used in the comparator mode its output is driven to supply extremes in either polarity depending on the input signal when this occurs the output devices in the amplifier become saturated and do not recover in time to perform as a linear amplifier when the circuit is changed into an amplifier therefore the bootstrap power supply 14 includes components so that it can limit supply voltages and thus limits the output excursions of the a d comparator amplifier 40 to make it recover more quickly after it has been overloaded during the compare phase this is accomplished by resistor 70 and two zener diodes 72.