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Vacuum tube cascode amplifier bias

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Vacuum tube cascode amplifier bias

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US3184687A - Push-pull power amplifier - Google Patents


Effective date : Year of fee payment : 4. Year of fee payment : 8. Year of fee payment : A stabilized Cascode Amplifier Circuit wherein the grid or gate control of the second stage of the cascaded input is provided by feedback of a portion of the output signal voltage. The circuit can be further enhanced by the inclusion of a unity gain follower between the first and third stage of the cascode amplifier circuit.

The basic cascode circuit has long been a favorite choice for input stages of amplifiers because of its simplicity, high gain and low noise characteristics. Its name is derived from "cascade-cathode" in which one part follows another in cascade but with the output of the first connected directly to the cathode of the second part.

The name "cascode" is even commonly used for transistor circuits in which there are no cathodes. Although the cascode circuit has several advantages, it has some significant limitations, especially when used in very high quality audio amplifiers or preamplifiers. In these high performance applications, the signal linearity lack of signal distortion , wide bandwidth and freedom from noise and drift due to aging or other disturbances becomes very important.

The present invention is a cascode amplifier circuit in which the bias voltage fo the cascode input is taken from the output resistor. This results in a simpler circuit structure having fewer power supply components and a surprising increase in performance. The circuit has lower noise, wider bandwidth and greater gain and phase stability than existing cascode amplifier circuits. In a preferred embodiment a unity gain follower can be directly coupled between the first and second stages of the cascode input circuit to offer further improvements in performance.

A detailed description of the preferred embodiments of the Cascode Amplifier is hereafter described with specific reference being made to the drawings in which:. In the current art an input signal is received by triode 10 which has its output connected directly to the cathode of triode The output of triode 12 is made directly to the grid of the third amplifier stage triode The output from the circuit is made across a cathode follower resistor 15 from which the circuit output is taken through capacitor Power is supplied to the circuit by power supply E1 through load resistor Biasing resistor 11 ensures proper operation of triode A separate bias power supply E2 is needed to control the input bias of the second stage triode Throughout this specification a circuit stage will refer to an amplifier stage made up of an electronic control valve and its associated biasing or load resistors.

The electronic control valves used in this circuit are normally three element devices. Inputs and outputs from electronic devices need to use at least two device terminals. For simplication inputs and outputs from three terminal devices are usually called out without labeling the actual terminal connections.

The present invention is shown in FIG. An input signal is received by triode 20 whose output taken from its plate is cascaded with the cathode of triode The output of triode 22 is used to control the grid of the third stage triode The circuit output is taken across the cathode follower resistors 25 and 27 through capacitor Power to the circuit is provided by power supply E1.

Biasing is provided to the second stage, triode 22, by taking a portion of the circuit output signal from the cathode follower resistors. Resistors 25 and 27 act as a voltage divider to provide a portion of the output voltage to triode By employing a cathode follower for impedance conversion into the circuit, it is very simple to split the load resistor into two parts and connect that junction to the input to the second stage of the cascode input triodes. This feedback loop puts a signal on the grid of the second triode that is out of phase with the input signal resulting in error cancellation.

This stabilized cascode amplifier circuit offers many advantages. The circuit eliminates the need for a separate bias power supply for the second stage of the cascode amplifier input. This is achieved because the stabilized cascode circuit reduces the gain of the second stage which in turn results in increased gain of the first stage of the cascode input circuit due to increased load impedance for the first stage input triode.

This is advantageous because the signal levels are higher in the second stage and the need for reduction of distortion is greater. By increasing the gain of the first stage of the cascode input the increased signal level overrides the noise produced by the second part of the cascode input to a greater degree.

The stabilized cascode circuit is no longer subject to the frequency dependent characteristics or drift of the power supply connected to the grid of the second stage of the conventional cascode amplifier circuit. Furthermore, the conventional technique of lowering noise by using the very large plate load resistance for the second stage is no longer necessary, thereby extending the high frequency bandwidth. The introduction of negative feedback used in the stabilized cascode circuit amplifier extends to direct current, and no troublesome low frequency phase shifts are introduced.

The effects of tube aging are largely compensated for by the negative feedback. While vacuum tubes are used in audio amplification for historical and audio fidelity reasons, transistors can also be used to implement the present invention.

Input signals are received by transistor The output of this first stage transistor is connected from its drain to the source of the second stage transistor The output of transistor 32 is connected to the gate of transistor The circuit's amplified signal out is taken through capacitor 36 and across the combination of source follower resistors 35 and The gate of transistor 32, the second stage transistor of the cascaded input, is biased by a voltage taken from the voltage divider formed by source follower resistors 35 and Bias resistor 31 and load resistor 33 are chosen to ensure proper transistor operation of the cascaded input transistors.

The field effect transistor version of the present invention operates as a direct replacement to the triode version. A third embodiment of the present invention includes the addition of an impedance converter or a unity gain follower directly coupled between the first and second stages of the disclosed cascode amplifier circuit.

In this circuit design the input signal is received by the first stage made up of triode 40 biased to an appropriate operating point by resistor Theoutput of triode 40 controls the grid of a second stage buffer triode 42 which has a load resistor The cathode of the buffer triode 42 is connected to the cathode of triode 44 which forms the third stage of the cascode amplifier circuit.

Triode 44 has a load resistor 47 and its output is used to control the grid of the fourth stage consisting of triode 46 and resistors 49 and The amplified circuit signal out is taken through capacitor 52 with the cathode follower resistor divided into two parts 49 and 51 to form a voltage divider.

A portion of the circuit's output signal is used to control the grid of the third stage triode The circuit operates similar to the embodiment as discussed with reference to FIG. Distortion is reduced since the operating conditions of the first part of the cascade input can be established independently of the operating conditions of the second part of the cascade input. Furthermore, the load resistor for the first stage along with the grid input of the second or buffer stage provides a more ideal linear load than driving the cathode of the second stage directly.

The low impedance of the buffer stage output lowers the distortion of the third stage triode, compared to connecting it directly to the first stage or input triode. In other words it is the accumulative effect of isolation, changed impedances, and different operating currents that provide the additional reduction in distortion. The disclosed buffered cascode amplifier circuit can also be implemented with solid state transistors. Referring to FIG. Transistor 62 is a p-channel enhancement mode MOS transistor whose source is connected to the source of a third stage transistor 64 which is an n-channel enhancement mode MOS transistor.

The output of transistor 64 is connected to the gate of a fourth stage transistor 66 arranged in a source-follower configuration. The amplifier circuit output signal is taken across voltage divider resistors 67 and 69 through capacitor A portion of the circuit output is fed back to the input of the third stage. The amount of feedback voltage is set by the ratio of the source-follower resistors. The feedback voltage is typically one-fourth to one-sixth of the total output voltage.

Resistors 61, 63 and 65 provide biasing or load resistance to ensure the correct operating parameters for the transistor circuit. With MOS transistors a further benefit emerges due to the availability of both n-channel and p-channel polarities.

By using a p-channel transistor for the second or buffer stage in a basic n-channel circuit the current consumption is reduced as the buffer transistor can operate with the same current as the third stage of the cascode input. Therefore, all the buffer stage current can be utilized to drive the third stage transistor rather than sharing it in a common load resistor. Additionally, without a biasing resistor on the second stage transistor 62, distortion is also reduced.

During circuit operation the direct current potential at the input of the third stage transistor 64 is raised, allowing a corresponding elevation of the feedback tap for its gate, and providing even lower distortion due to increased negative feedback. The signal gain of the overall circuit is actually increased while distortion is reduced, because the buffer stage allows the first stage transistor 60 to operate more optimally. The combined effects of the addition of a buffer stage is more than would be commonly expected by its inclusion.

What is claimed is: 1. An electron tube cascode-cascade amplifier comprising: a cascode input stage including a cascode pair comprising first and second electron tubes, said first tube acting as the signal input tube;. The amplifier according to claim 1 further including feedback bias means for connecting the cathode output of said output tube to the grid of said second tube to provide a dynamic operating bias thereto. A transistorized cascode-cascade amplifier comprising: a cascode input stage including a cascode pair comprising first and second transistors, said first transistor acting as the signal input transistor;.

The amplifier according to claim 3 further including feedback bias means for connecting the output of said output transistor to the control terminal of said second transistor to provide a dynamic operating bias thereto. A cascode-cascade amplifier comprising: a cascode input stage including a cascode pair comprising first and second amplifying devices, said first device acting as the signal input device;. The amplifier according to claim 5 further including feedback bias means for connecting the output of said output device to the control input of said second device to provide a dynamic operating bias thereto.

A cascode input stage for an amplifier comprising: a cascode input stage including a cascode pair comprising first and second amplifying devices, said first device acting as the signal input device;. USA en. EPA3 en. Method and apparatus for microwave predistorter linearizer with electronic tuning.

Linear high-voltage drive stage and cathode-follower high-fidelity power amplifier implementing same. Electret microphone buffer circuit with significantly enhanced power supply rejection. USB2 en. El Diwany et al. G, No. El-Diwany et al. EPA2 en. KRB1 en.


The cascode is an amazing device

EPA2 Circuit arrangement with a transistor output circuit and a protection circuit for limiting the output current of the transistor output circuit. US Amplifier having reduced power dissipation and improved slew rate. US Transient noise free type amplifier circuit. US Reference voltage generating circuit. WOA1 Amplifier circuit. EPA1 Electronic power overload protection circuit.

transistor or vacuum tube) with no input signal applied. Most often, bias simply a bias voltage is applied to a transistor in an electronic amplifier to.

What impact did the transistor have on digital electronics?


Post Your Comments? The Cascode is a two-stage amplifier that consists of a common-emitter stage feeding into a common-base stage. Cascode , Consists , Common. In modern circuits, the Cascode is often constructed from two …. Circuits , Cascode , Constructed. Cascode , Comparison , Common. The bias resistors for this circuit are calculated in an example problem Cascode.

UNIT-1 BIASING OF DISCRETE BJT AND MOSFET DC LOAD LINE AND OPERATING POINT

vacuum tube cascode amplifier bias

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The cascode amplifier is used to enhance the performance of an analog circuit. The utilization of cascode is a common method which can be used in the applications of transistors as well as vacuum tubes.

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Use Cascode in a sentence

Grid leak — is the small current through the grid of a thermionic valve into the circuit which feeds the grid. It is an inherent operating characteristic of triodes and other vacuum tubes. This current is caused by the small negative EMF which is present in… … Wikipedia. Electronic amplifier — A practical amplifier circuit An 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. In… … Wikipedia. Low to medium power valve amplifiers for frequencies below… … Wikipedia. Valve audio amplifier - technical — Circuitry and performance Characteristics of valves Valves are very high input impedance near infinite in most circuits and high output impedance devices.

The cascode amplifiers provide equal voltage and power since each of the clone which now use vacuum tubes, thus employing the existing power supply.

Effective date : Year of fee payment : 4. Year of fee payment : 8. Year of fee payment :

A recent discussion reminded me of an idea to use the shunt cascode topology to direct couple to a single-ended output. It required some extra power supply rails, including a fairly large negative rail. Anyways, the more recent discussion reminded me of a thread discussing a novel way of direct coupling two stages by stacking the power supplies. Applying this idea to my original shunt cascode brainstorm lead me to this:. We have a shunt cascode input stage. The output resistor R2 idles at about 75V across it.

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Transistors transformed the world of electronics and had a huge impact on computer design. Transistors made of semiconductors replaced tubes in the construction of computers. By replacing bulky and unreliable vacuum tubes with transistors, computers could now perform the same functions, using less power and space. Transistors make excellent electronic switches. They can turn currents on and off billions of times per second. Digital computers use transistors as a basic mechanism for storing and moving data. The single most important invention of the 20th century was the transistor, according to some researchers and analysts.

Retrograde Cascode Be sure to see post number for a revsion on this post. Inverted Cascode Before we explore inverted-cascode circuits, let's do a quick review of the plain, conventional, textbook cascode topology, particularly its How , When , What , and Why. We begin, oddly enough, at the end with the cascode's Why. In other words, Why did we need someone to create cascode topology?




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  1. Arnon

    Only recently became your reader and immediately subscriber. Thanks for the post.

  2. Jonas

    It agree, it is an excellent idea

  3. Cachamwri

    I apologise, but this variant does not approach me. Perhaps there are still variants?