Operational amplifier having selectable inputs

• Main Author: MOYAL MIKI
• Format: Patent
• Language: English; French; German
• Published: 31.03.1999
• Edition: 6
• Subjects: AMPLIFIERS; BASIC ELECTRONIC CIRCUITRY; ELECTRICITY; PULSE TECHNIQUE

There is disclosed an operational amplifier (10) which is arranged for sensing the voltages provided by a plurality of input voltage sources and which diminishes the level of noise at the operational amplifier output resulting from the selection of the input voltage sources. The operational amplifier (10) includes a first amplification stage (12) having first and second voltage sensing inputs (38, 40), a common input (36), and an output (28, 34), and a second amplification stage (16) having an input (42) and an output (52). Switch means (14) are disposed between the first stage output (28, 34) and the second stage input (42) for selectively coupling the amplified signal at the first stage output resulting from an input signal at the first input (40) to the second stage input (42) or the amplified signal at the first stage output resulting from an input signal at the second input (38) to the second stage input (42). Because the switch means (14) is disposed between the first (12) and second (16) amplification stages, the noise coupled into the operational amplifier (10) is not amplified by the first amplification stage and hence, the noise at the output of the operational amplifier (10) is deceased by a factor equal to the gain of the first amplification stage (12).