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Circuit for Selecting Analog Signal Having Absolute Value of Greater Magnitude

IP.com Disclosure Number: IPCOM000034161D
Original Publication Date: 1989-Jan-01
Included in the Prior Art Database: 2005-Jan-26
Document File: 3 page(s) / 45K

Publishing Venue

IBM

Related People

Wooton, RM: AUTHOR

Abstract

Two bipolar analog voltage signals, which represent load currents as sampled by current sense resistors, are converted to absolute values of their respective magnitudes. The signal having the absolute value of greater magnitude is automatically selected and presented at a single output for use by following circuits. A selector circuit includes a precision rectifier or absolute value circuit 1 receiving an analog voltage signal A as its input and having an output voltage signal eo1, which is always negative irrespective of the polarity of the input signal A. The output signal eo1 from the circuit 1 is supplied as one input to a summing amplifier circuit 2.

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Circuit for Selecting Analog Signal Having Absolute Value of Greater Magnitude

Two bipolar analog voltage signals, which represent load currents as sampled by current sense resistors, are converted to absolute values of their respective magnitudes. The signal having the absolute value of greater magnitude is automatically selected and presented at a single output for use by following circuits. A selector circuit includes a precision rectifier or absolute value circuit 1 receiving an analog voltage signal A as its input and having an output voltage signal eo1, which is always negative irrespective of the polarity of the input signal
A. The output signal eo1 from the circuit 1 is supplied as one input to a summing amplifier circuit 2. A second precision rectifier or absolute value circuit 3 has an analog voltage signal B as its input and has an output voltage signal eo2, which is always negative irrespective of the polarity of the input signal B. The output signal eo2 from the circuit 3 is supplied as a second input to the summing amplifier circuit 2. Each of the circuits 1 and 3 is the same so that only the circuit 1 will be described in detail. The circuit 1 includes operational amplifiers 4 and 5, which are in an inverting condition. The circuit 1 has resistors 6, 7, 8, and 9 with each having the same resistance and a resistor 10 having a resistance of one- half of the resistance of each of the resistors 6-9. The output signal eo2 from the circuit 3 is fed back to the circuit 1 through a resistor 11, which has the same resistance as each of the resistors 6-9. The lower (greater in absolute value because both are negative voltages) of the two signals eo1 and eo2 will conduct current from the node at the input of the operational amplifier to which it is connected. For example, if the output signal eo2 from the circuit 3 has a greater negative value than eo1, more current will be drawn from the input of the operational amplifier 5 than is drawn from the input of an operational amplifier 12 of the circuit 3. As a result, the voltage at the input to the operational amplifier 5 will decrease to reduce the amplitude of the output signal eo1 so that it has less effect on the circuit 3. This results in the output signal eo1 from the circuit 1 going to zero and the output signal eo2 from the circuit 3 retaining its value. Accordingly, the magnitude of the voltage at the output of the summing amplifier circuit 2 is the output signal eo2 and in...