Measurement of Ciss, Coss, Crss

In summary, Ciss, Coss, and Crss are important measurements for an n-channel JFET, but there is limited information available on how to measure them. Ciss is a combination of Cgd and Cgs when drain and source are shorted, Coss is a combination of Cgd and Cds when gate and source are shorted, and Crss is just Cgd when all three are shorted together. It is important to have a capacitance meter that can accurately measure in the pF range and to account for stray capacitance in the fixture.
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I'm trying to devise some circuits to measure Ciss, Coss, and Crss for an n-channel JFET, and I'm running into trouble. I know these measurements are made all the time, but can't find any information anywhere about how one would go about actually measuring them. I am also confused by Crss in general because if the gate, drain, and source are all shorted where does Cgd come into play?

Ciss is when drain and source are shorted to each other, gives you gate-drain capacitance (Cgd) in parallel with gate-source capacitance (Cgs) so Ciss = Cgd + Cgs

Coss is when gate and source are shorted, gives you Cgd + Cds (drain-source capacitance)

Crss is when gate, source, and drain are all shorted together, gives you Cgd
 
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Do you have access to a good quality capacitance meter that can measure accurately down in the pF range? Are you familiar how to null out the effects of the stray capacitance of your fixture?
 

1. What is the purpose of measuring Ciss, Coss, and Crss?

The measurement of Ciss, Coss, and Crss is important for understanding the electrical characteristics of a transistor, which is a fundamental component in electronic devices. These measurements help determine the input capacitance (Ciss), output capacitance (Coss), and reverse transfer capacitance (Crss) of a transistor, which are crucial for designing and optimizing circuits.

2. How are Ciss, Coss, and Crss measured?

Ciss, Coss, and Crss are typically measured using specialized equipment, such as a network analyzer or a semiconductor parameter analyzer. These instruments apply specific voltage and current signals to the transistor and measure the resulting capacitances at various frequencies.

3. What factors can affect the accuracy of Ciss, Coss, and Crss measurements?

The accuracy of Ciss, Coss, and Crss measurements can be affected by factors such as temperature, bias voltage, and frequency. It is important to control these variables during the measurement process to ensure accurate results.

4. How are Ciss, Coss, and Crss values used in circuit design?

The values of Ciss, Coss, and Crss are used in circuit simulations to predict the behavior of the transistor in a specific circuit. These values are also used in calculations for determining important parameters such as gain, bandwidth, and stability of a circuit.

5. Why are Ciss, Coss, and Crss measured at different frequencies?

The capacitances of a transistor can vary with frequency, so it is important to measure Ciss, Coss, and Crss at different frequencies to get a more complete picture of the transistor's behavior. This is especially important for high-frequency applications where the capacitance values can significantly impact the performance of the circuit.

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