Designing a Stepped Attenuator Using Pin Diode Switches in Microwave Office

[mudassarhanif]

i am designing a stepped attenuator using pin diode as a switch in microwave office. i am having difficulty in using pin diode as a switch. i knw it is operate in forward bias and open in reverse bias. if i am giving a rf signal between 300 Mhz to 3 Ghz then how can i switch it to reverse bias? secondly there is something called bias wat is it?

 

[sirius0]

sounds like you need a multilayer semi conductor device like a http://en.wikipedia.org/wiki/TRIAC" . It can conduct for the positive or negative half cycles simply by firing the gate.
Bias is the tendency for a diode to conduct better with the current flowing in one direction as opposed to flowing in the reverse direction.

 

[sirius0]

Hmm there is more to your PIN doide than I thought! I need to learn a little too. (the following link directly opens a PDF linked from wikipedia) http://www.microsemi.com/micnotes/701.pdf" is what I am looking at.

 

[mudassarhanif]

any bdy who can tell me how we can calculate the values of low pass filter which is used to on and off (to switch) the pin diodes?

 

[berkeman]

i am designing a stepped attenuator using pin diode as a switch in microwave office. i am having difficulty in using pin diode as a switch. i knw it is operate in forward bias and open in reverse bias. if i am giving a rf signal between 300 Mhz to 3 Ghz then how can i switch it to reverse bias? secondly there is something called bias wat is it?

http://www.radio-electronics.com/info/circuits/diode-rf-attenuator/pin-diode-switch.php

.

 

[mudassarhanif]

@ berkeman

can u give me some more specific details?

 

[berkeman]

@ berkeman

can u give me some more specific details?

The link gives a pretty good basic overview of what you are asking about. What don't you understand about it?

How many steps are you designing into your attenuator? Are you following it with an amplifier? Are you going to have a 50 Ohm output impedance out of the attenuator? With or without a follower amp?

You need to show some effort here. We do not do your projects for you here on the PF.

 

[mudassarhanif]

i am designing attenuator with tee and pi attenuator circuit. the pin diode switch which i want to use here is work as follow

a) when the switch is open, then all the frequency pass through transmission line bypassing attenuator.

b) when switch is closed, then it will pass through attenuator circuit by passing transmission line.

this means that when i transmit frequency more than the set limit let say 3 Ghz then the switch must be in "on" state to attenuate it and when the frequency is in range then it bypasses the attenuation circuit and pass through transmission line.

 

[berkeman]

i am designing attenuator with tee and pi attenuator circuit. the pin diode switch which i want to use here is work as follow

a) when the switch is open, then all the frequency pass through transmission line bypassing attenuator.

b) when switch is closed, then it will pass through attenuator circuit by passing transmission line.

this means that when i transmit frequency more than the set limit let say 3 Ghz then the switch must be in "on" state to attenuate it and when the frequency is in range then it bypasses the attenuation circuit and pass through transmission line.

You want it to be a frequency-dependent attenuator? That would just be a filter, right?

Or will you have a separate control that you use to turn the attenuator on and off? What rate will you likely be switching the attenuator? And is the requirement for steps gone now? Just on and off?

 

[mudassarhanif]

at the moment i am just trying to attenuate it, so there is no need of stepping for the time being. you are right that can be a filter but how can i put pin diode which works as a switch and pass the frequency through the transmission line in off state?

there is no issue of switching rate.

 

[berkeman]

at the moment i am just trying to attenuate it, so there is no need of stepping for the time being. you are right that can be a filter but how can i put pin diode which works as a switch and pass the frequency through the transmission line in off state?

there is no issue of switching rate.

Use the technique shown in the link, and have two PIN diode switches. One that passes the signal through to the transmission line, and the other that does something else (sorry that I'm not 100% tracking what you are trying to do).

 

[mudassarhanif]

the thing is that i don't knw how it works?

consider there is a frequency (let say 3Ghz), it will pass through the diode and to the attenuator circuit.

now let say that the incoming frequency is 2Ghz and it is the required frequency...the switch which is placed before the attenuator circuit should be open now. and all the frequency passes through the transmission line.

how can i control the on off of this switch?

 

[berkeman]

the thing is that i don't knw how it works?

consider there is a frequency (let say 3Ghz), it will pass through the diode and to the attenuator circuit.

now let say that the incoming frequency is 2Ghz and it is the required frequency...the switch which is placed before the attenuator circuit should be open now. and all the frequency passes through the transmission line.

how can i control the on off of this switch?

As shown in the link (you can probably find others with Google), you control the bias on the diode to turn it on or off. If you pull up on the bias resistor, that forward biases the diode, and it is "on". If you pull down on the bias resistor, that reverse biases the resistor and open circuits it "off".

All of that assumes that the "RF Out" to the right is terminated with 50 Ohms or some other real resistance to ground, so that the bias resistor has something to bias against.