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Copy of Compare Cascode vs. Single MOSFET Amplifier - on Sun, 07/09/2023 - 17:35

User-1688869330
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This example shows the bandwidth improvement that results from a cascode amplifier configuration (right-side circuit), compared to a single transistor amplifier configuration (left side).

In these circuits, identical transistor models are used. They are "datasheet" based behavioral models with typical small-signal NFET characteristics. This includes an internal Miller capacitance or Crss, which is set to 10 pF.

In the single transistor circuit, the Miller Theorem states that the effective value of Crss is increased by a factor of (1.0 + A), where A is the gain of the amplifier. In this case the factor is (1.0 + gfs * Rload), or 16x, so the effective Crss = 160 pF. Then the low-pass RC time constant of the input source resistance and the net input capacitance sets the amplifier bandwidth at just under 2 MHz.

For the cascode amplifier, the voltage at the drain of transistor m2 has only very small variation, so the Miller effect is largely suppressed for that device. Transistor m3 amplifies these small voltage changes, but because the current in the Miller capacitance of m3 is drawn from the low impedance gate bias circuit, it does not limit the bandwidth of the amplifier.

You can move the probes around and look at the time-domain or frequency-domain signals at any point in the circuit, to gain more understanding of these component interactions.

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TEST STAGE Compare Cascode vs. Single MOSFET Amplifier

Galina
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Galina

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Member of the PartQuest Explore team.

Description

This example shows the bandwidth improvement that results from a cascode amplifier configuration (right-side circuit), compared to a single transistor amplifier configuration (left side).

In these circuits, identical transistor models are used. They are "datasheet" based behavioral models with typical small-signal NFET characteristics. This includes an internal Miller capacitance or Crss, which is set to 10 pF.

In the single transistor circuit, the Miller Theorem states that the effective value of Crss is increased by a factor of (1.0 + A), where A is the gain of the amplifier. In this case the factor is (1.0 + gfs * Rload), or 16x, so the effective Crss = 160 pF. Then the low-pass RC time constant of the input source resistance and the net input capacitance sets the amplifier bandwidth at just under 2 MHz.

For the cascode amplifier, the voltage at the drain of transistor m2 has only very small variation, so the Miller effect is largely suppressed for that device. Transistor m3 amplifies these small voltage changes, but because the current in the Miller capacitance of m3 is drawn from the low impedance gate bias circuit, it does not limit the bandwidth of the amplifier.

You can move the probes around and look at the time-domain or frequency-domain signals at any point in the circuit, to gain more understanding of these component interactions.

About text formats

Copy of Compare Cascode vs. Single MOSFET Amplifier - on Tue, 09/08/2020 - 13:17

alpha_peach
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Description

This example shows the bandwidth improvement that results from a cascode amplifier configuration (right-side circuit), compared to a single transistor amplifier configuration (left side).

In these circuits, identical transistor models are used. They are "datasheet" based behavioral models with typical small-signal NFET characteristics. This includes an internal Miller capacitance or Crss, which is set to 10 pF.

In the single transistor circuit, the Miller Theorem states that the effective value of Crss is increased by a factor of (1.0 + A), where A is the gain of the amplifier. In this case the factor is (1.0 + gfs * Rload), or 16x, so the effective Crss = 160 pF. Then the low-pass RC time constant of the input source resistance and the net input capacitance sets the amplifier bandwidth at just under 2 MHz.

For the cascode amplifier, the voltage at the drain of transistor m2 has only very small variation, so the Miller effect is largely suppressed for that device. Transistor m3 amplifies these small voltage changes, but because the current in the Miller capacitance of m3 is drawn from the low impedance gate bias circuit, it does not limit the bandwidth of the amplifier.

You can move the probes around and look at the time-domain or frequency-domain signals at any point in the circuit, to gain more understanding of these component interactions.

About text formats

Copy of Compare Cascode vs. Single MOSFET Amplifier - on Sat, 03/21/2020 - 16:32

qqq00142
Designer230359

qqq00142

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Description

This example shows the bandwidth improvement that results from a cascode amplifier configuration (right-side circuit), compared to a single transistor amplifier configuration (left side).

In these circuits, identical transistor models are used. They are "datasheet" based behavioral models with typical small-signal NFET characteristics. This includes an internal Miller capacitance or Crss, which is set to 10 pF.

In the single transistor circuit, the Miller Theorem states that the effective value of Crss is increased by a factor of (1.0 + A), where A is the gain of the amplifier. In this case the factor is (1.0 + gfs * Rload), or 16x, so the effective Crss = 160 pF. Then the low-pass RC time constant of the input source resistance and the net input capacitance sets the amplifier bandwidth at just under 2 MHz.

For the cascode amplifier, the voltage at the drain of transistor m2 has only very small variation, so the Miller effect is largely suppressed for that device. Transistor m3 amplifies these small voltage changes, but because the current in the Miller capacitance of m3 is drawn from the low impedance gate bias circuit, it does not limit the bandwidth of the amplifier.

You can move the probes around and look at the time-domain or frequency-domain signals at any point in the circuit, to gain more understanding of these component interactions.

About text formats

Copy of Compare Cascode vs. Single MOSFET Amplifier - on Wed, 03/11/2020 - 17:51

eaudic
Designer226778

eaudic

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Description

This example shows the bandwidth improvement that results from a cascode amplifier configuration (right-side circuit), compared to a single transistor amplifier configuration (left side).

In these circuits, identical transistor models are used. They are "datasheet" based behavioral models with typical small-signal NFET characteristics. This includes an internal Miller capacitance or Crss, which is set to 10 pF.

In the single transistor circuit, the Miller Theorem states that the effective value of Crss is increased by a factor of (1.0 + A), where A is the gain of the amplifier. In this case the factor is (1.0 + gfs * Rload), or 16x, so the effective Crss = 160 pF. Then the low-pass RC time constant of the input source resistance and the net input capacitance sets the amplifier bandwidth at just under 2 MHz.

For the cascode amplifier, the voltage at the drain of transistor m2 has only very small variation, so the Miller effect is largely suppressed for that device. Transistor m3 amplifies these small voltage changes, but because the current in the Miller capacitance of m3 is drawn from the low impedance gate bias circuit, it does not limit the bandwidth of the amplifier.

You can move the probes around and look at the time-domain or frequency-domain signals at any point in the circuit, to gain more understanding of these component interactions.

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Compare Cascode vs. Single MOSFET Amplifier

stefan
Designer145316

stefan

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7 years 3 months

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Description

This example shows the bandwidth improvement that results from a cascode amplifier configuration (right-side circuit), compared to a single transistor amplifier configuration (left side). In these circuits, identical transistor models are used. They are "datasheet" based behavioral models with typical small-signal NFET characteristics. This includes an internal Miller capacitance or Crss, which is set to 10 pF.In the single transistor circuit, the Miller Theorem states that the effective value of Crss is increased by a factor of (1.0 + A), where A is the gain of the amplifier. In this case the factor is (1.0 + gfs * Rload), or 16x, so the effective Crss = 160 pF. Then the low-pass RC time constant of the input source resistance and the net input capacitance sets the amplifier bandwidth at just under 2 MHz.For the cascode amplifier, the voltage at the drain of transistor m2 has only very small variation, so the Miller effect is largely suppressed for that device. Transistor m3 amplifies these small voltage changes, but because the current in the Miller capacitance of m3 is drawn from the low impedance gate bias circuit, it does not limit the bandwidth of the amplifier.You can move the probes around and look at the time-domain or frequency-domain signals at any point in the circuit, to gain more understanding of these component interactions.

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Under development Compare Cascode vs. Single BJT Transistor Amplifier

Mike Donnelly
Designer19

Mike Donnelly

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11 years 1 month

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Member of the PartQuest Explore Development Team. Focused on modeling and simulation of analog, mixed-signal and multi-discipline systems covering a broad range of applications, including power electronics, controls and mechatronic systems.

Description

This example shows the bandwidth improvement that results from a cascode amplifier configuration (right-side circuit), compared to a single transistor amplifier configuration (left side). In these circuits, identical transistor models are used. They are ideal models that have no internal Miller capacitance or Ccb, The Miller capacitance is represented by an external 10 pF discrete capacitor for each device.In the single transistor circuit, the effective value of the Miller capacitance is increase by the current gain of the transistor, hfe = 100. So the RC time constant of the load resistance with that increased capacitance value, reduces the amplifier bandwidth by almost the same factor.For the cascode amplifier, the voltage at the collector of the CE transistor q2 does not change significantly, so the Miller effect is largely suppressed for that device. The CB transistor q3 acts as a simple current follower. Because the current in the Miller capacitance of q3 is drawn from the low impedance bias circuit, it does not significantly impact the base current of q3.You can move the probes around and look at the time-domain or frequency-domain signals at any point in the circuit, to gain more understanding of these component interactions.

About text formats

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