Varicap Diodes

g3cwi · 2012-02-13 11:11

Hi there

I want to use a pin from the prop to control the voltage across a varicap diode. I need a nice big swing - say 10-2 Volts. Is there an easy way of doing this? I'm imagining some sort of PWM being used. Anyone got a clever idea/circuit?

Cheers

Richard

Leon · 2012-02-13 11:26

I'd use a DAC and an op amp. PWM could be used, but it will need a lot of filtering to avoid noise which could cause problems in your application. It's an Rx, isn't it?

g3cwi · 2012-02-13 11:34

Hi Leon

Yes, it's an RX. If I go down your route I would need an 8 bit (or more) DAC (possibly serial) and ideally something that can control a higher voltage than the digital input. Does such a beast exist?

This looks useful:
http://www.analog.com/static/imported-files/data_sheets/AD5263.pdf EDIT: but way too expensive!

Cheers

Richard

Leon · 2012-02-13 11:40

There are lots of them, up to 12 bits or more, with I2C interfaces. You will need an op amp, as I said, to get your voltage range.

Circuitsoft · 2012-02-13 11:44

{{
                   12V
                    &#61463;
                    &#61628;120&#937;      100K&#937;     100K&#937;   100K&#937;     0.1µF
                    &#9507;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#61629;&#61630;&#9472;&#9523;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#61629;&#61630;&#9472;&#9523;&#9472;&#9472;&#9472;&#9472;&#61629;&#61630;&#9472;&#9472;&#9472;&#9472;&#9472;&#9523;&#9472;&#61611;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#61610; C for tank circuit
   DUTY_MODE pin &#61609;&#9472;&#61465;&#61467;SSM3K15CT    &#61612;&#61613;&#61614;1µF    &#61612;&#61613;&#61614;1µF    &#9484;&#61606;&#61607;&#9496;
                    &#61464;              &#61464;         &#61464;        &#61464; Varicap
}}

g3cwi · 2012-02-13 12:00

Thanks Circuitsoft. I might well try that first as the DAC route will be more costly.

Circuitsoft · 2012-02-13 15:07

Another simpler option is a basic duty-mode output into an Op-Amp to amplify your signal.

Duane C. Johnson · 2012-02-13 15:20

What frequency range do you need the oscillator to run at?

Duane J

g3cwi · 2012-02-14 01:51

Duane

The application is not part of an oscillator, it's a software controlled filter.

Regards

Richard

g3cwi · 2012-02-14 01:52

Circuitsoft wrote: »

Another simpler option is a basic duty-mode output into an Op-Amp to amplify your signal.

Not too sure what you mean Circuitsoft?

Regards

Richard

Varicap Diodes

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