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A differential amplifier is a type of electronic amplifier that amplifies the difference between two input voltages but suppresses any voltage common to the two inputs. [1] It is an analog circuit with two inputs and + and one output , in which the output is ideally proportional to the difference between the two voltages:
A fully differential amplifier (FDA) is a DC-coupled high-gain electronic voltage amplifier with differential inputs and differential outputs. In its ordinary usage, the output of the FDA is controlled by two feedback paths which, because of the amplifier's high gain, almost completely determine the output voltage for any given input.
The emitter junctions of these amplifier stages are fed by the collectors of a third differential pair (Q2/Q6). The output currents of Q2/Q6 become emitter currents for the differential amplifiers. Simplified, the output current of an individual transistor is given by i c = g m v be. Its transconductance g m is (at T = 300 K) about g m = 40 I C.
The op-amp inverting amplifier is a typical circuit, with parallel negative feedback, based on the Miller theorem, where the op-amp differential input impedance is apparently decreased to zero Zeroed impedance uses an inverting (usually op-amp) amplifier with enormously high gain A v → ∞ {\displaystyle A_{v}\to \infty } .
The input stage of modern amplifiers is usually a differential amplifier with a transconductance characteristic. This means the input stage takes a differential input voltage and produces an output current into the second stage. The transconductance is typically very high — this is where the large open loop gain of the amplifier is generated.
The equation is true for any frequency signal, assuming an ideal op amp (though a real op-amp has limited bandwidth). The op amp's low-impedance output isolates the load of the succeeding stages, so this circuit has the same response independent of its load. If a constant DC voltage is applied as input, the output voltage is zero.
An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the magnitude of a signal (a time-varying voltage or current). It is a two-port electronic circuit that uses electric power from a power supply to increase the amplitude (magnitude of the voltage or current) of a signal applied to its input ...
The simplified circuit above is like the differential amplifier in the limit of R 2 and R g very small. In this case, though, the circuit will be susceptible to input bias current drift because of the mismatch between R f and R in. To intuitively see the gain equation above, calculate the current in R in: