Analog voltage selector circuit with selected voltage detection

Claim 1

A selector circuit for providing an output signal having a voltage accurately numerically equalling the one analog voltage input signal having the greatest voltage of a given polarity among a plurality of analog voltage input signals, said circuit comprising: a plurality of operational amplifiers each having an inverting input connection and an output connection; a plurality of input resistors for receiving said input signals and each connected to a respective one of said input connections; a biasing resistor connected between a circuit output conductor and a source of biasing voltage; a plurality of first diodes each connected between said circuit output conductor and a respective one of said amplifier output connections; a plurality of feedback resistors each connected between said circuit output conductor and the input connection of a respective one of said amplifiers; said first diodes each being oriented so as to be forward biased and thus to connect the respective amplifier output to said circuit output conductor and to permit feedback via the associated feedback resistor to said input connection only as long as the output voltage of the respective amplifier exceeds the voltage of said circuit output conductor, and to become reverse biased when the output voltage of the respective amplifier is less than that of the output conductor whereby only the first diode associated with said amplifier having the greatest input potential remains forward biased to provide output to said circuit output conductor; a plurality of second diodes each connected between a respective one of said amplifer output connections and the input connection for the same amplifier; said second diodes each being oriented so as to normally be reverse biased but to become forward biased in response to reverse biasing of the corresponding one of said first diodes, whereby direct feedback is effected for all of said amplifiers but the one associated with said greatest analog voltage input signal so that the output connection of each of said amplifiers having such direct feedback settles to one diode voltage drop above nominal ground; a plurality of detector circuits each associated with the output connection of one of said amplifiers; said detectoR circuits each being responsive to voltage changes at the output connection of the corresponding amplifier so as to provide a first output condition when the corresponding first diode is forward biased and a second output condition when said corresponding first diode is reverse biased, whereby said output conditions of said detector circuits are representative of which of said analog input voltages is the greatest; a grounded base transistor; digital signal output means connected to the transistor for providing said first output condition when said transistor is substantially saturated and said second output condition when said transistor is non-conductive, a third diode having an anode connected to said output connection of the associated amplifier and having a cathode connected to the emitter of said transistor; a second biasing resistor connected from between said diode and said transistor to a source of biasing voltage; said third diode and transistor being oriented so that said third diode is forward biased and said transistor is nonconductive when the first diode connected to the associated amplifier is reverse biased, and said third diode is reverse biased and said transistor is saturated when said first diode connected to the associated amplifier is forward biased; said digital signal output means comprises NAND gate means biased to serve as a signal inverter and having one input connected to the collector of said transistor.