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Please consider using {{Expert-subject}} to associate this request with a WikiProject | A cascode is an arrangement of electronic active devices that combines two amplifier stages for increased output resistance and avoiding the Miller effect, resulting in high gain with increased bandwidth. The cascode also improves reverse isolation since there is no direct coupling from the output to input (same reason it avoids the miller effect). The cascode works by keeping the Vds or Vce of the gain transistor constant. The cascode arrangement usually refers specifically to the combination of a transconductance amplifier stage with a current buffer stage. This is the same as a common emitter followed by a common base. Image File history File links Broom_icon. ...
Image File history File links Emblem-important. ...
The output impedance, source impedance, or internal impedance of an electronic device is the opposition exhibited by its output terminals to the flow of an alternating current (AC) of a particular frequency as a result of resistance, induction and capacitance. ...
In electronics, the Miller effect describes the fact that a capacitance between input and output of an amplifier is multiplied by (with is the voltage gain) in a electrical circuit. ...
In electronics, gain is usually taken as the mean ratio of the signal output of a system to the signal input of the system. ...
Bandwidth is the difference between the upper and lower cutoff frequencies of, for example, a filter, a communication channel, or a signal spectrum, and is typically measured in hertz. ...
Common emitter amplifier, voltage divider bias (CEVDB) circuit configuration A common emitter is a type of electronic amplifier stage based on a bipolar transistor in series with a load element such as a resistor. ...
Common base amplifier In electronics, common base refers to a type of bipolar transistor circuit configuration in which a transistor is connected such that its base terminal is wired to the ground or common rail of the circuit (or can be considered so for AC signals). ...
The cascode (sometimes verbified to cascoding) is a universal technique for improving analog circuit performance, applicable to both vacuum tubes and transistors. The word was first used in an article by F.V. Hunt and R.W. Hickman in 1939, in a discussion for application in low-voltage stabilizers. They proposed a cascade of two triodes (first one with common cathode, the second one with common grid) as a replacement of a pentode. It has been suggested that this article or section be merged with Analog electronics. ...
Structure of a vacuum tube diode Structure of a vacuum tube triode In electronics, a vacuum tube, electron tube, or (outside North America) thermionic valve or just valve, is a device used to amplify, switch or modify a signal by controlling the movement of electrons in an evacuated space. ...
Assorted discrete transistors A transistor is a semiconductor device, commonly used as an amplifier or an electrically controlled switch. ...
Year 1939 (MCMXXXIX) was a common year starting on Sunday (link will display the full calendar) of the Gregorian calendar. ...
A voltage regulator is an electrical regulator designed to automatically maintain a constant voltage level. ...
Simplified diagram of a triode. ...
Diagram of a copper cathode in a Daniells cell. ...
The control grid is an electrode used in thermionic valves (vacuum tubes) used to modulate the flow of electrons in the cathode to anode or plate circuit. ...
This article does not cite any references or sources. ...
With the rise of integrated circuits, transistors became "cheap" in terms of silicon die area. In MOSFET technology especially, cascoding can be used in current mirrors to create relatively "constant" current sources. Integrated circuit of Atmel Diopsis 740 System on Chip showing memory blocks, logic and input/output pads around the periphery Microchips with a transparent window, showing the integrated circuit inside. ...
The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is by far the most common field-effect transistor in both digital and analog circuits. ...
A current mirror is a circuit designed to copy a current flowing through one active device by controlling the current in another active device of a circuit, keeping the output current constant regardless of loading. ...
An example of cascode employed in User Controlled Technology is the MOS cascode BF908 (Q101) in the receiver of the RONJA optical datalink project. The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is by far the most common field-effect transistor in both digital and analog circuits. ...
Ronja device installed on a balcony. ...
Free Space Optics (FSO) is a telecommunication technology that uses light propagating in free space to transmit data between two points. ...
Cascode circuits are also found in modulators, particularly those for amplitude modulation. The upper device supplies the audio signal, and the lower is the RF amplifier device. In telecommunications, modulation is the process of varying a periodic waveform, i. ...
Amplitude modulation (AM) is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. ...
It has been suggested that this article or section be merged with Radio waves. ...
FET Cascode circuit example
Figure 1: N-channel cascode amplifier (neglecting biasing details) Figure 1 shows an example of cascode amplifier with a Common source amplifier, after Vin driving a Common gate amplifier. Image File history File links No higher resolution available. ...
R1, R2 and RE provide bias in this common emitter amplifier (CEVDB) circuit configuration Biasing in electronics is the method of applying a predetermined voltage and current to the junction of a transistor to set the appropriate quiescent point. ...
Common source amplifier with input bias and capacitively coupled input and output. ...
Common gate amplifier A common-gate amplifier is one of the common configurations of FET electronic amplifier. ...
The major advantage of this circuit arrangement stems from the placement of the upper FET as the load of the input (lower) FET's output terminal (drain). Because at operating frequencies the upper FET's gate is effectively grounded, the upper FET's source voltage (and therefore the input transistor's drain) is held at nearly constant voltage during operation. This dramatically reduces the Miller feedback capacitance from the lower FET's drain to gate, compared to what would happen if the upper FET was replaced by a typical inductive/resistive load (and the output taken from the input transistor's drain instead). Thus, the upper transistor permits the lower FET to operate at maximum input impedance and minimum negative (Miller) feedback, improving its gain. This makes the cascode circuit excellent for high-frequency applications where the Miller feedback would otherwise be prohibitive. In electronics, the Miller effect describes the fact that a capacitance between input and output of an amplifier is multiplied by (with is the voltage gain) in a electrical circuit. ...
The upper FET does not suffer from Miller problems because its gate is electrically grounded, and any stray capacitance from its drain to its source will not reduce its gain because the voltages are in phase.
Thus, the cascode configuration offers higher input impedance and much higher overall gain than a similar, one-transistor circuit would.
The cascode arrangement is also very stable. Its output is effectively isolated from the input both electrically and physically. The lower transistor has nearly constant voltage at both drain and source and thus there is essentially "nothing" to feed back into its gate. The upper transistor has nearly constant voltage at its gate and source. Thus, the only nodes with significant voltage on them are the input and output, and these are separated by the central connection of nearly constant voltage and by the physical distance of two transistors. Thus in practice there is little feedback from the output to the input. Metal shielding is both effective and easy to provide between the two transistors for even greater isolation when required. This would be difficult in one-transistor amplifier circuits, which at high frequencies would require neutralization.
As shown, the cascode circuit using two "stacked" FETs imposes some restrictions on the two FETs -- namely, the upper FET must have higher IDSS than the lower, or the circuit may not bias properly (the lower FET's drain voltage may fall too low, causing it to leave saturation). Because IDSS tends to be a relatively "loose" parameter in FET manufacture, the cascode circuit built with FETs requires careful selection for the pair, increasing costs.
The cascode circuit can also be built using bipolar transistors, or even one FET and one BJT. In the latter case, the BJT must be the upper transistor; otherwise, the (lower) BJT will always saturate (unless extraordinary steps are taken to bias it).
Advantages The cascode arrangement offers high gain, high stability, and high input impedance. The parts count is very low for a two-transistor circuit.
Basically it provides high gain at larger bandwidth.
Disadvantages The cascode circuit requires two transistors and requires a relatively high supply voltage. For the two-FET cascode, both transistors must be biased with ample VDS in operation, imposing a lower limit on the supply voltage.
Dual-gate MOSFET as cascode A dual-gate MOSFET often functions as a "one-transistor" cascode. Common in the front ends of sensitive VHF receivers, a dual-gate MOSFET is operated as a common-source amplifier with the primary gate (usually designated "gate 1" by MOSFET manufacturers) connected to the input and the 2nd gate grounded (bypassed). Internally, there is one channel covered by the two adjacent gates; therefore, the resulting circuit is electrically a cascode composed of two FETs, the common lower-drain-to-upper-source connection merely being that portion of the single channel that lies physically adjacent to the border between the two gates. Very high frequency (VHF) is the radio frequency range from 30 MHz to 300 MHz. ...
See also - Tetrode transistor
- Pentode transistor
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