| 摘要 |
A switchable constant gain summer circuit (10) has been provided. The summer circuit selectively amplifies a plurality of input signals while maintaining a constant dc current flowing through a load which maintains a constant gain for the summer circuit. The summer circuit includes a plurality of amplifier circuits (12, 16) being respectively responsive to a plurality of input signals wherein each one of amplifier circuits has a control input and common first and second outputs for respectively providing first and second output signals. A plurality of control means (14, 18) responsive to a plurality of control signals is included for alternately providing first and second voltages to each one of the control inputs of the amplifier circuits. A load circuit (20) is coupled to the common first and second outputs of the amplifier circuits wherein a DC bias through the load circuit is substantially constant. Also, an output stage (22) coupled to the common first and second outputs of the plurality of amplifier circuits is included for respectively providing first and second summed voltages.
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