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Laser Receiver - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement

Post subject: Laser Receiver Posted: Fri Aug 11, 2006 6:20 am


Joined: Fri Aug 11, 2006 6:07 am
Posts: 5
I need to design a laser receiver circuit which would receive laser pulses in the red region of the spectrum (around 630nm wavelegth), the laser pulses carry an RF ripple of around 315MHz. I built a current to voltage converter using a transimpedance amplifier with resistor feedback and simulated it on Multisim, it seems to be working fine. But I have a couple of problems, firstly, the transimpedance amplifier is an inverting amplifier so I need to reinvert the signal or get it straight the first time with minimum distortion. Secondly, I need to find a way to have two outputs for the device, one giving the equivalent output voltage of the signal (DC with a 315MHz ripple) and the other with AC coupling (just the 315MHz ripple). And the last problem is that I need to make the system as noise-immune as possibe. If anyone can help me or point me to where I can find something that would help I'd appreciate it a lot.


Post subject: Posted: Fri Aug 11, 2006 7:55 am


Joined: Fri Feb 17, 2006 12:07 pm
Posts: 218
Location: London UK
My first reaction is try to separate the dc from the 315MHz components at as early a stage as possible.
What is the source/spectrum of the likely interference?


Post subject: Posted: Fri Aug 11, 2006 8:15 am


Joined: Fri Aug 11, 2006 6:07 am
Posts: 5
Well, there's no specific source, it's just thermal noise, shot noise and other regular sources of interference. I can put two parallel transimpedance amplifiers, one to separate the RF alone and the other just to convert the signal to voltage as a whole, but the problem is that I get a weird transient of a relatively low frequency whenever there's a pulse transition when I try to separate the RF alone, I guess it's due to the presence of the L and C in the transimpedance amplifier, I'm still trying to figure out how to remove that.


Post subject: Posted: Fri Aug 11, 2006 1:14 pm


Joined: Fri Aug 11, 2006 6:07 am
Posts: 5
I think I was able to do it but I just have one more question left. I'm supposed to add an enable signal to the circuit, what would be the best way to implement that? Is it through a transistor that passes Vcc to the whole circuit when it receives the needed signal or through a transistor that passes the output signal when it receives the enable signal?


Post subject: Posted: Fri Aug 11, 2006 1:23 pm

Site Admin

Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany

To answer to your last question, I recommend to use the first option, i.e. to control over the Vcc supply voltage. This will promise a full isolation and will block any leakage or residual signals to the output.

Best regards,

- IR

Posted  11/12/2012

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