The input offset voltage (
) is a parameter defining the
differential DC
voltage
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to m ...
required between the inputs of an
amplifier
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 may increase the power significantly, or its main effect may be to boost the v ...
, especially an
operational amplifier
An operational amplifier (often op amp or opamp) is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output. In this configuration, an op amp produces an output potential (relative to c ...
(op-amp), to make the output zero (for voltage amplifiers, 0
volts
The volt (symbol: V) is the unit of electric potential, electric potential difference (voltage), and electromotive force in the International System of Units (SI). It is named after the Italian physicist Alessandro Volta (1745–1827).
Defini ...
with respect to ground or between differential outputs, depending on the output type).
Details
An ideal op-amp amplifies the differential input; if this input difference is 0 volts (i.e. both inputs are at the same voltage), the output should be zero. However, due to manufacturing process, the differential input transistors of real op-amps may not be exactly matched. This causes the output to be zero at a non-zero value of differential input, called the input offset voltage.
Typical values for
are around 1 to 10 mV for cheap commercial-grade op-amp
integrated circuits
An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...
(IC). This can be reduced to several microvolts if nulled using the IC's offset null pins or using higher-quality or
laser-trimmed devices. However, the input offset voltage value may drift with temperature or age.
Chopper amplifiers actively measure and compensate for the input offset voltage, and may be used when very low offset voltages are required.
Input bias current
Input may refer to:
Computing
* Input (computer science), the act of entering data into a computer or data processing system
* Information, any data entered into a computer or data processing system
* Input device
* Input method
* Input port (disa ...
and
input offset current
Input may refer to:
Computing
* Input (computer science), the act of entering data into a computer or data processing system
* Information, any data entered into a computer or data processing system
* Input device
* Input method
* Input port (disa ...
also affect the net offset voltage seen for a given amplifier. The voltage offset due to these currents is separate from the input offset voltage parameter and is related to the impedance of the signal source and of the feedback and input impedance networks, such as the two resistors used in the basic inverting and non-inverting amplifier configurations.
FET
The field-effect transistor (FET) is a type of transistor that uses an electric field to control the flow of current in a semiconductor. FETs (JFETs or MOSFETs) are devices with three terminals: ''source'', ''gate'', and ''drain''. FETs contr ...
-input op-amps tend to have lower input bias currents than
bipolar-input op-amps, and hence incur less offset of this type.
Input offset voltage is symbolically represented by a voltage source that is in series with either the positive or negative input terminal (it is mathematically equivalent either way). Normally input offset voltage is measured in the terms of input voltage applied at the non-inverting terminal to make output zero.
[http://www.ti.com/lit/an/sloa059/sloa059.pdf page 3]
References
{{reflist
External links
Analog Devices tutorial on op-amp input offset voltage and mitigation techniques
Electrical parameters