negative voltage regulator

PMT's have been counting photons since before I was born. Heck, Schottky discovered shot noise in vacuum photo diodes in 1918.

Mostly is just some device someone else made, and you just have to hook it up right.

George H.

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George Herold
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That's really cool, thanks. Do you ever reuse the old pcb blocks, or just make up new ones each new project?

(My proto's lead to a pcb(s), and once that's working I don't need the proto anymore.)

George H.

Reply to
George Herold

Gerhard,

Love your work! We've been thinking through the idea of starting a business around standard RF building blocks just like this - standard sizes, mounting, power feeds, digital options (SPI, I2C, MGT) and using Ipex or MMCX jump cables in preference to soldering semi-rigid.

All done on very thin PCB with edge-launch connectors that can fit SIL pins or allow the whole module to be soldered down, the idea being that you can prototype with jump leads perhaps using a motherboard, then go to low volume mfg by making a custom motherboard using published footprints, and soldering the modules down.

That way, anyone who can design a block diagram for e.g. a VNA, or a special RF receiver, can prototype it, and take it quickly to production, without all the difficulty of local impedance matching and power supplies, etc. Or they can sell the motherboard only, or open source a design, with constructors buying suitable modules to complete it.

Initial modules would be filters, gain blocks, mixers, synthesizers, DDS, ADC/DAC and ARM control blocks. And generic motherboards... What have I missed?

Comments invited from anyone...

Clifford Heath.

Reply to
Clifford Heath

The SRF doesn't matter; the impedance does. A 100 farad 0603 cap would have a very low SRF, but it would still be a useful bypass at 1 GHz.

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John Larkin         Highland Technology, Inc 

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John Larkin

Why the 100 ohms?

Is the scope at the end of the cable 50 ohms?

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John Larkin         Highland Technology, Inc 

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John Larkin

What's the capacitance of that APD?

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John Larkin         Highland Technology, Inc 

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John Larkin

I've done some circuit-specific 4-layer PCBs and thrown in various test things here and there. US8 and other weird IC adapters, filters, signal splitters, connector adapters, coplanar waveguides, meander lines, RF relays, things like that. Here's one:

formatting link

You could put a lot of little circuits on, say, a 6" square board.

Panelized mouse-bite boards are interesting too. Easy to break up and solder down to a motherboard.

Make it bigger, 12" square, and sell it all or themed snapped-off sections. Opamps, adapters, filters, logic.

Anybody who submits a good idea for a tile could get a board free.

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John Larkin         Highland Technology, Inc 

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John Larkin

I was not aware of a stereo zoom with such a large working distance.

Unfortunately, it still forces you to hold your neck in an awkard position to view through the eyepieces. I used to be able to do this for long hours, but as I aged, it became more difficult and painful. The Canon allows me to view a HDMI monitor heads up, and I can move my head anywhere as needed for comfortable and easy viewing. I can also capture images or motion video to the pc, which cannot be done with the microscope without adding an expensive camera. Also, I can use many different filters, such as UV or visible light, polarizing, and other types. These cannot be used with a microscope.

I'm wondering if the field of view of the microscope is wide enough to show parts near maximum magnification while still allowing you to see the soldering iron tip some distance away. My stereo microscope does not. The Canon does.

Reply to
Steve Wilson

You can do exactly the same thing by straightening the leads so the come straight out the side of the ic.

Also, some wideband parts require the central tab be connected to solid ground. You cannot do this when mounting the chip upside down.

It is very hard to identify a chip when it is upside down. Months later you will forget where everything is. You have to put some kind of marking on the copper to tell what kind of chip it is.

Unfortunately, some ic packages like J-lead have to be mounted upside down. But they may be available with leads.

Reply to
Steve Wilson

Get a Mantis. They are wonderful. The LED illuminated "Compact" is probably best, with a 4x lens. Well, I like 4x but I'm naturally nearsighted. The 8x field of view is kinda small.

I wonder if there is a Chinese knock-off version of the Mantis.

I don't like cameras/monitors as much. The Mantis is wonderfully clear and 3D.

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John Larkin         Highland Technology, Inc 

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John Larkin

Hmm don't know. (just handy in the parts box.)

Yeah, well daisy chained through 'scope and onto

50 ohm comaparator-> counter. I might just run it into a comparator.

George H.

Reply to
George Herold

About 2 pF. The C vs V bias curve is different. Fig 5 here.

formatting link

GH

Reply to
George Herold

OK, at 2 pF there's not much point in cascoding it.

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John Larkin         Highland Technology, Inc 

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John Larkin

Why a resistor to ground at all?

I usually source terminate stuff like that, a resistor in series with the opamp output, to the connector.

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John Larkin         Highland Technology, Inc 

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John Larkin

I'm not sure what that means? Am I cascoding it now?

To be honest I'm not really understanding my pulse shape. I thought I'd be getting a sharp edge and then RC recharge of the diode/opamp/stray capacitance.

George H.

Reply to
George Herold

Well, the circuit is still very uncertain. If this node is made available to students, then having 100 ohms there the line won't ring too much when they forget to terminate it.

OK, thanks, I'll see what that looks like.

George H.

Reply to
George Herold

No. A cascode would be a common-base transistor between the photodiode and the amp.

I guess if you're counting photons from an avalanche PD, you don't care a lot about speed or noise. The 1K load slows things down and adds noise, but that's probably OK.

The capacitance of the PD plus the input c of the opamp, and a little PCB capacitance, might add up to 5 or 6 pF maybe. That makes a 5-6 ns time constant with 1K.

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John Larkin         Highland Technology, Inc 

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John Larkin

If you source terminate, put maybe 47 ohms from the opamp output to the connector, it will work nicely with a 50 ohm scope or with a 1M scope... no cable reflections in either case. Of course, using a 50 ohm scope will cut the gain in half.

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John Larkin         Highland Technology, Inc 

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John Larkin

Wait! Yikes! There's that 400K too!

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John Larkin         Highland Technology, Inc 

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John Larkin

The 6x SLWD lens is great. Its long working distance keeps the lens out of the way of the soldering iron. ;-)

They're not cheap but neither are the people using them.

Reply to
krw

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