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Figure 3: Gain-boosted current mirror with op-amp feedback to increase output resistance MOSFET version of gain-boosted current mirror; M 1 and M 2 are in active mode, while M 3 and M 4 are in ohmic mode and act like resistors. The operational amplifier provides feedback that maintains a high output resistance.
Representative schematic of a current-feedback op-amp or amplifier. The current-feedback operational amplifier (CFOA or CFA) is a type of electronic amplifier whose inverting input is sensitive to current, rather than to voltage as in a conventional voltage-feedback operational amplifier (VFA).
Many commercial op-amp offerings provide a method for tuning the operational amplifier to balance the inputs (e.g., "offset null" or "balance" pins that can interact with an external voltage source attached to a potentiometer). Alternatively, a tunable external voltage can be added to one of the inputs in order to balance out the offset effect.
Figure 7: Typical op-amp current source. The simple transistor current source from Figure 4 can be improved by inserting the base-emitter junction of the transistor in the feedback loop of an op-amp (Figure 7). Now the op-amp increases its output voltage to compensate for the V BE drop. The circuit is actually a buffered non-inverting amplifier ...
An operational amplifier (often op amp or opamp) is a DC-coupled electronic voltage amplifier with a differential input, a (usually) single-ended output, [1] and an extremely high gain. Its name comes from its original use of performing mathematical operations in analog computers .
Like a standard operational amplifier, the OTA also has a high impedance differential input stage and may be used with negative feedback. [3] But the OTA differs in that: The OTA outputs a current while a standard operational amplifier outputs a voltage. The OTA is usually used "open-loop"; without negative feedback in linear applications.
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Continuous-time devices work more like an array of transistors or op amps which can operate at their full bandwidth. The components are connected in a particular arrangement through a configurable array of switches. During circuit design, the switch matrix's parasitic inductance, capacitance and noise contributions must be taken into account.