Post subject: PIN diode switch - how to change biasing Posted:
Sat Sep 03, 2005 12:51 am
I 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.
Problem : -
I used on
series diode betweeen two microstrip lines terminated in Ports.
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.
Can some please help me out here.
You can also write to firstname.lastname@example.org
Post subject: PIN DiodesPosted: Sat Sep 03, 2005 11:07
PIN diodes 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 overvoltage.
2. Coupling around the diode - parallel microstrip lines might provide
that if there's enough length where they're parallel
aren't what you think they are. (Not too likely, I know, but worth mentioning/checking)