Chopper (electronics)
Encyclopedia
A chopper circuit is used to refer to numerous types of electronic switching devices and circuits. The term has become somewhat ill-defined, and as a result is much less used nowadays than it was perhaps 30 or more years ago.
Essentially, a chopper is an electronic switch
that is used to interrupt one signal under the control of another. Most modern uses also use alternative nomenclature which helps to clarify which particular type of circuit is being discussed. These include:
amplifiers. Some types of signal that need amplifying can be so small that an incredibly high gain
is required, but very high gain DC amplifiers are much harder to build with low offset and 1/
noise, and reasonable stability and bandwidth. It's much easier to build an AC
amplifier instead. A chopper circuit is used to break up the input signal so that it can be processed as if it were an AC signal, then integrated back to a DC signal at the output. In this way, extremely small DC signals can be amplified. This approach is often used in electronic instrumentation where stability and accuracy are essential; for example, it is possible using these techniques to construct pico-voltmeters and Hall sensor
s.
The input offset voltage
of amplifiers becomes important when trying to amplify small signals with very high gain. Because this technique creates a very low input offset voltage amplifier, and because this input offset voltage does not change much with time and temperature, these techniques are also called "Zero-Drift" amplifiers (because there is no drift in input offset voltage with time and temperature). Related techniques that also give these Zero-drift advantages are Auto-zero and Chopper-stabilized Amplifiers.
Auto-zero amplifiers use a secondary auxiliary amplifier to correct the input offset voltage of a main amplifier. Chopper-stabilized amplifiers use a combination of auto-zero and chopper techniques to give some excellent DC precision specifications.
Some example chopper and auto-zero amplifiers are LTC2050,MAX4238/MAX4239 and OPA333.
Essentially, a chopper is an electronic switch
Switch
In electronics, a switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another....
that is used to interrupt one signal under the control of another. Most modern uses also use alternative nomenclature which helps to clarify which particular type of circuit is being discussed. These include:
- switched mode power suppliesSwitched-mode power supplyA switched-mode power supply is an electronic power supply that incorporates a switching regulator in order to be highly efficient in the conversion of electrical power...
, including DC to DC converterDC to DC converterA DC-to-DC converter is an electronic circuit which converts a source of direct current from one voltage level to another. It is a class of power converter.- Usage :...
s. - Speed controllers for DC motorDC motorA DC motor is an electric motor that runs on direct current electricity.-Brush:The brushed DC electric motor generates torque directly from DC power supplied to the motor by using internal commutation, stationary magnets , and rotating electrical magnets.Like all electric motors or generators,...
s - Class D Electronic amplifierElectronic amplifierAn electronic amplifier is a device for increasing the power of a signal.It does this by taking energy from a power supply and controlling the output to match the input signal shape but with a larger amplitude...
s - Switched capacitorSwitched capacitorA switched capacitor is an electronic circuit element used for discrete time signal processing. It works by moving charges into and out of capacitors when switches are opened and closed. Usually, non-overlapping signals are used to control the switches, so that not all switches are closed...
filterElectronic filterElectronic filters are electronic circuits which perform signal processing functions, specifically to remove unwanted frequency components from the signal, to enhance wanted ones, or both...
s - Variable Frequency DriveVariable frequency driveA variable-frequency drive is a system for controlling the rotational speed of an alternating current electric motor by controlling the frequency of the electrical power supplied to the motor. A variable frequency drive is a specific type of adjustable-speed drive...
Chopper amplifiers
One classic use for a chopper circuit and where the term is still in use is in chopper amplifiers. These are DCDirect current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
amplifiers. Some types of signal that need amplifying can be so small that an incredibly high gain
Gain
In electronics, gain is a measure of the ability of a circuit to increase the power or amplitude of a signal from the input to the output. It is usually defined as the mean ratio of the signal output of a system to the signal input of the same system. It may also be defined on a logarithmic scale,...
is required, but very high gain DC amplifiers are much harder to build with low offset and 1/
noise, and reasonable stability and bandwidth. It's much easier to build an ACAlternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
amplifier instead. A chopper circuit is used to break up the input signal so that it can be processed as if it were an AC signal, then integrated back to a DC signal at the output. In this way, extremely small DC signals can be amplified. This approach is often used in electronic instrumentation where stability and accuracy are essential; for example, it is possible using these techniques to construct pico-voltmeters and Hall sensor
Hall effect sensor
A Hall effect sensor is a transducer that varies its output voltage in response to a magnetic field. Hall effect sensors are used for proximity switching, positioning, speed detection, and current sensing applications....
s.
The input offset voltage
Input offset voltage
Input offset voltage is the differential DC voltage required between the inputs of an amplifier, especially an operational amplifier, to make the output zero .* Typical values are around 1-10mV for cheap commercial-grade operational amplifier integrated circuits, but can...
of amplifiers becomes important when trying to amplify small signals with very high gain. Because this technique creates a very low input offset voltage amplifier, and because this input offset voltage does not change much with time and temperature, these techniques are also called "Zero-Drift" amplifiers (because there is no drift in input offset voltage with time and temperature). Related techniques that also give these Zero-drift advantages are Auto-zero and Chopper-stabilized Amplifiers.
Auto-zero amplifiers use a secondary auxiliary amplifier to correct the input offset voltage of a main amplifier. Chopper-stabilized amplifiers use a combination of auto-zero and chopper techniques to give some excellent DC precision specifications.
Some example chopper and auto-zero amplifiers are LTC2050,MAX4238/MAX4239 and OPA333.