Gilbert cell
Encyclopedia
In electronics
, the Gilbert cell is a transistor circuit used as an analog multiplier
and frequency mixer
, first described by Barrie Gilbert
in 1968. The advantage of this circuit is the output current is an accurate multiplication of the (differential) base currents of both inputs. As a mixer, its balanced operation cancels out many unwanted mixing products, resulting in a "cleaner" output.
stages formed by emitter-coupled transistor pairs (Q1/Q4, Q3/Q5) whose outputs are connected (currents summed) with opposite phases. 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, therefore the output currents of these stages are linearly dependent on these emitter currents and the respective input voltages. Combining the two difference stages' output currents yields four-quadrant operation.
A functionally equivalent circuit can be constructed using field-effect transistor
s (JFET
, MOSFET
) or vacuum tubes.
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...
, the Gilbert cell is a transistor circuit used as an analog multiplier
Analog multiplier
In electronics, an analog multiplier is a device which takes two analog signals and produces an output which is their product. Such circuits can be used to implement related functions such as squares , and square roots....
and frequency mixer
Frequency mixer
In electronics a mixer or frequency mixer is a nonlinear electrical circuit that creates new frequencies from two signals applied to it. In its most common application, two signals at frequencies f1 and f2 are applied to a mixer, and it produces new signals at the sum f1 + f2 and difference f1 -...
, first described by Barrie Gilbert
Barrie Gilbert
Barrie Gilbert was born in 1937 in Bournemouth, England. He is well-known for his invention of numerous analog circuit concepts, holding over 100 patents worldwide, and for the discovery of the Translinear Principle and a class of related topologies loosely referred to as the Gilbert cell, one of...
in 1968. The advantage of this circuit is the output current is an accurate multiplication of the (differential) base currents of both inputs. As a mixer, its balanced operation cancels out many unwanted mixing products, resulting in a "cleaner" output.
Function
The Gilbert cell consists of two differential amplifierDifferential amplifier
A differential amplifier is a type of electronic amplifier that amplifies the difference between two voltages but does not amplify the particular voltages.- Theory :Many electronic devices use differential amplifiers internally....
stages formed by emitter-coupled transistor pairs (Q1/Q4, Q3/Q5) whose outputs are connected (currents summed) with opposite phases. 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, therefore the output currents of these stages are linearly dependent on these emitter currents and the respective input voltages. Combining the two difference stages' output currents yields four-quadrant operation.
A functionally equivalent circuit can be constructed using field-effect transistor
Field-effect transistor
The field-effect transistor is a transistor that relies on an electric field to control the shape and hence the conductivity of a channel of one type of charge carrier in a semiconductor material. FETs are sometimes called unipolar transistors to contrast their single-carrier-type operation with...
s (JFET
JFET
The junction gate field-effect transistor is the simplest type of field-effect transistor. It can be used as an electronically-controlled switch or as a voltage-controlled resistance. Electric charge flows through a semiconducting channel between "source" and "drain" terminals...
, MOSFET
MOSFET
The metal–oxide–semiconductor field-effect transistor is a transistor used for amplifying or switching electronic signals. The basic principle of this kind of transistor was first patented by Julius Edgar Lilienfeld in 1925...
) or vacuum tubes.
Applications
A Gilbert cell can be used as:- A small signal precise four-quadrant multiplierAnalog multiplierIn electronics, an analog multiplier is a device which takes two analog signals and produces an output which is their product. Such circuits can be used to implement related functions such as squares , and square roots....
(with condition that both inputs are small compared with VT (Thermal voltage=0.025V) - A large signal phase detectorPhase detectorA phase detector or phase comparator is a frequency mixer, analog multiplier or logic circuit that generates a voltage signal which represents the difference in phase between two signal inputs...
(with condition that both inputs are great compared with VT) - A modulator in a communications application (with condition that only one input is small compared with VT while the other input is greater)
- A pre-processing circuit in a Flash ADCFlash ADCA Flash ADC is a type of analog-to-digital converter that uses a linear voltage ladder with a comparator at each "rung" of the ladder to compare the input voltage to successive reference voltages...
to reduce the number of comparators in this architecture. This is called a folding ADC.