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Copy of Compare Cascode vs. Single MOSFET Amplifier - on Mon, 07/10/2023 - 16:52

Designer247418

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

Designer247313

Member for

1 year 8 months

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Welcome to the community!!

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

TEST STAGE Compare Cascode vs. Single MOSFET Amplifier

Designer21

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11 years 4 months

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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

Designer234625

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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

Designer230359

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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

Designer226778

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5 years 4 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.

About text formats

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