Electronics > RF, Microwave, Ham Radio

Analog amplifiers for pulsed LIDAR

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-- My first post :)

Hi All,

I am SW engineer with limited experience in analog/RF circuits.

I am designing a laser radar. The Tx will send a very short electrical pulse (pulse width =5ns, current = 35A ,wavelength = 905 um) to laser diode (MPPC). The RX shall consist of photo detector diode , amplification stage and range circuit (TDC-GP21).

This is the recommended Rx configuration from the datasheets :

 I read many articles on the internet about how much noise exists in such Rx circuits and I would like to avoid such things.

I have two options for the amplification stage
1- two cascaded OPA855 each one has gain of 20x . First stage is transimpedance configuration.
2- Use one IC which make all amplification without any external components such as ADA8282 (LNA+PGA), it has 4 channels and I was planning to use two of them in series.

The Rx will be implemented on 2-layer PCB

I appreciate if any expert here give some advices. I am also open to any other solutions/ICs.

That's a confusing circuit - normally the first stage is explicitly differential (an opamp), and the diode bias is negative so that the first stage output is positive.  And I don't get the capacitor on the input of the amp.  Which datasheet?

There is a great book by Jerald Graeme called "PhotoDiode Amplifiers"- it is the Bible for designing this stuff.  A good EE library would have it.

Another good resource is the data sheet for the OPA656, a wideband amp used in these apps.  The OPA858 is another stellar part to look at.  The configuration you show in your block is quite approximate but "generally" ok.  The cap to ground is a parasitic C- its there in reality but is a nuisance, there certainly shouldn't be a physcial cap installed there!  These are circuits of real finesse, I respect your trying but its a tough design.  Read Graeme's book cover to cover and you've got a chance.

You may want to look at purpose built LIDAR receivers from Maxim (now ADI) and others- the MAX40658-60.  These are what are used in industry.

Many thanks for the Book and the advice. Highly appreciated.
I will definitely read the book and try to build its circuits.

I went through the book. I learned something new. I am missing one thing! -->  All circuits has fixed gain.

I was thinking to add a variable feedback Resistor which I could control via I2C to achieve variable gain receiver.

is there a better approach for doing so ?


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