impedance matching in a circuit

[rakesh.kumar78910]

i have designed my circuit, but i am confused about impedance matching. i know we can use a resistor for matching, but is it possible to use a capacitor or inductor for matching the impedance in a circuit.

 

[audioguru]

Most circuits do not match impedances.
If the load impedance is matched to the output impedance of a circuit then the power is high but the voltage is cut in half.
Most circuits do not use much power so they use a low impedance driving a high impedance to reduce signal voltage loss.

 

[ljcox]

I agree with Audio.

You only need to match impedance if you want to maximise the power transfer from source to the load.

For example, a radio transmitter/receiver. In this case you want max power transfer from/to the antenna.

In the case of a telephone, you need the impedance of the phone matched to the impedance of the line for this reason and also to minimise reflections due to any mismatch.

If talking over a long distance, any reflection from the phone will be heard at the other end as an echo.

However, the Z matching is not perfect, so telehone exchanges have to switch in Echo Cancellers on long distance connections.

 

[bountyhunter]

i have designed my circuit, but i am confused about impedance matching. i know we can use a resistor for matching, but is it possible to use a capacitor or inductor for matching the impedance in a circuit.

QWhat is it supposed to do?

 

[audioguru]

You designed a circuit that you did not show to us. You don't even tell us what the circuits are. We don't know what you want to match to what.
We explained that most impedances ARE NOT MATCHED because if you match them then you lose signal voltage. Many circuits need all the signal voltage they can get.

 

[ljcox]

Please post your circuit so we can advise you.

We are not mind readers.

 

[bountyhunter]

Please post your circuit so we can advise you.

We are not mind readers.

20 years I worked in the technical support department at Natl Semi wishing I could have said that to the people calling me....... boss wouldn't have liked it.

 

[rakesh.kumar78910]

i apologise for not posting my circuit. the input given is a RF signal , which has 50 ohm and the output is a laser diode having 25 ohm impedance value. the working frequency is 2.6GHz . the impedance matching is to be done between the RF signal and the laser diode. i need to use a capacitor and inductor for matching the impedance and we even avoid using resistor to do matching because it create noise and consume power.

 

[user_88]

Why are you not using an RF transformer to accomplish the impedance match?

...It turns out that one wavelength of 2.6 GHz, using a typical coaxial cable, is only about 3 inches long. There might be some difficulty implementing a matching transformer that is constructed out of coaxial cable.

 

[ljcox]

I agree. A transformer would be the best way to match the impedances.

I don't see how a Cap & an inductor would match the impenance.

However, I've had little experience with microwave RF, so I don't know how to design a transformer for 2.6 GHz.

Hopefully someone else will know.

 

[misterT]

I agree with Audio.
You only need to match impedance if you want to maximise the power transfer from source to the load.

I also agree. I just want to add the word "efficiency". Impedance matching maximizes the power transfer efficiency.

 

[Nigel Goodwin]

I also agree. I just want to add the word "efficiency". Impedance matching maximizes the power transfer efficiency.

I wouldn't use the word 'efficiency' as the maximum theoretical efficiency is only 50%, which is pretty inefficient.

 

[misterT]

I wouldn't use the word 'efficiency' as the maximum theoretical efficiency is only 50%, which is pretty inefficient.

Ok.. yes. But you get that maximum by matching the impedances