# Zin/zout for high-pass filter help?

• xhuang23
In summary, the conversation discusses the calculation of Zin and Zout for a high-pass filter circuit with a transfer function of Vout/Vin = R/(R+1/jwC). The speaker is unsure about the value of Zout and asks for clarification on whether to include R or just Xc. The conversation also mentions the dependence of Zout on whether the Vin terminals are connected to anything. The listener suggests calculating Zin and Zout based on the information provided.

## Homework Statement

An expression for Zin (impedance seen fromthe input) and Zout (impedance seen from the output) of the high-pass filter circuit with respect to frequency is: ?

## The Attempt at a Solution

i have, bythe way, equation for transfer function already. Vout/Vin= R/(R+1/jwC). i am pretty sure Zin=Xc=1/jwC but not so sure about zout. would it be R+Xc or just R? i know at high frequency the imaginary part drops, so its just R.

or maybe i am doing this wrong. should i do the same thing for zout/zin as vout/vin?

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It would be much easier to help you if you would post a schematic of your filter circuit.

it is typical high-pass filter circuit so i didnt think to post a pic. the Vin source was supposed to be 1vpk. the R value i calculated from the fc (cutoff freq) value =1.5kHz.

xhuang23 said:

## Homework Statement

An expression for Zin (impedance seen fromthe input) and Zout (impedance seen from the output) of the high-pass filter circuit with respect to frequency is: ?

## The Attempt at a Solution

i have, bythe way, equation for transfer function already. Vout/Vin= R/(R+1/jwC). i am pretty sure Zin=Xc=1/jwC but not so sure about zout. would it be R+Xc or just R? i know at high frequency the imaginary part drops, so its just R.

or maybe i am doing this wrong. should i do the same thing for zout/zin as vout/vin?

How do you get Zin=Xc=1/jwC? Zin is the impedance calculated at the Vin terminals. Isn't R1 part of that impedance?

Zout will depend on whether or not anything is connected to the Vin terminals. If the filter is driven by a voltage source (having zero ohms internal impedance), then Zout is the impedance seen at the Vout terminals with the Vin terminals shorted (by the impedance of the driving source).

Try calculating Zin and Zout with this information.

I would like to clarify that the expression for Zin and Zout in a high-pass filter circuit depends on the specific circuit design and component values. In general, Zin would equal the impedance of the input source, while Zout would equal the impedance of the output load. However, in a high-pass filter, the impedance seen from the input and output may vary with frequency due to the presence of a capacitor. Therefore, it is important to calculate Zin and Zout at the specific frequency of interest.

In this case, the expression for Zin would be Xc = 1/jwC, as you have correctly identified. This represents the impedance of the capacitor at a given frequency. For Zout, it would depend on the output load. If the output load is purely resistive, then Zout would simply be equal to the resistance value. However, if the output load also contains a capacitor, then the expression for Zout would also involve the impedance of that capacitor.

To determine the exact expression for Zout, you can use the same approach as for Vout/Vin. By writing the output voltage as a function of the input voltage, you can find the equivalent impedance seen from the output. It is important to note that at high frequencies, the capacitor's impedance will decrease, but it will still have an effect on the overall impedance seen from the output.

In summary, the expressions for Zin and Zout in a high-pass filter circuit can vary depending on the specific design and frequency of interest. It is important to carefully consider all components in the circuit and their effects on the impedance seen from the input and output.

## 1. What is a high-pass filter?

A high-pass filter is an electronic circuit that allows high frequency signals to pass through while attenuating low frequency signals. It is used to remove unwanted low frequency noise from a signal.

## 2. How does a high-pass filter work?

A high-pass filter works by using a capacitor and a resistor to create a voltage divider. The capacitor allows high frequency signals to pass through, while the resistor attenuates low frequency signals. This results in a signal with a higher frequency range.

## 3. What is the purpose of using zin and zout in a high-pass filter?

Zin and zout are used in a high-pass filter to match the input and output impedance of the filter to the source and load impedance, respectively. This ensures maximum power transfer and prevents signal reflections.

## 4. How do I choose the right values for zin and zout in a high-pass filter?

The values for zin and zout can be calculated using the source and load impedance and the desired cutoff frequency of the filter. It is important to choose values that will provide the desired impedance matching and prevent signal loss.

## 5. Can I use zin and zout values from any high-pass filter?

No, the zin and zout values will vary depending on the specific high-pass filter design and the source and load impedance. It is important to calculate or use the recommended values for your specific filter design.