Post subject: PIN diode switch - how to change biasing
Posted: Sat Sep 03, 2005 12:51 am
working on Switching circuits at 2-4GHz range using PIN diodes.
I am designing the circuit in ADS. Started with simple most series
PIN diode switch, but facing some problem in that.
I used on series diode betweeen two microstrip
lines terminated in Ports.
the diode has been biased throguh
high - low transmission lines. I gave bias voltage at P terminal
of diode of around 2 Volts, the diode is in forward bias. Even though
I change voltage value to be -25 volts, the switch does not come
in OFF condition... i.e. S21 is still less than 1 dB.
some please help me out here.
You can also write
PIN DiodesPosted: Sat Sep 03, 2005 11:07 am
don't really turn on by voltage - they reach a low-impedance state
by (forward) current. So there has to be enough current flowing
in the forward direction to give the proper impedance. In the reverse
(off) direction, the applied ("DC") bias must (significantly) exceed
the peak voltage of the RF.
If you're sure you have those
two necessary conditions, then there are only a couple of possibilities:
1. Bad diode - PIN diodes can be damaged by both overcurrent and
2. Coupling around the diode - parallel microstrip
lines might provide that if there's enough length where they're
3. Impedances aren't what you think they are. (Not too
likely, I know, but worth mentioning/checking)