| 摘要 |
A transconductance amplifier circuit, which may used in a subscriber line interface circuit, transforms a single ended input voltage into a precise, single ended output current, in a manner that is effectively independent of respective voltage supply rails, and which can be operated at a very low quiescent current. An operational amplifier is configured as a unity gain buffer whose output stage is coupled in circuit with first current flow paths of first and second current mirrors. A single ended output of the output stage serves as an input terminal and is coupled via a negative feedback path to a first, inverting input of the operational amplifier. Second current flow paths of the pair of current mirrors are coupled to an output port, which supplies an output current linearly proportional to the composite input voltage applied to the input terminal. An auxiliary current mirror circuit pair may be cross-coupled to the first and second current mirrors to supply to a second output port a current that is equal and opposite to the output current. These two equal and opposite polarity currents may be coupled to respective tip and ring output amplifiers for application to a telephone wireline pair.
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