Recent Posts

Pages: [1] 2 3 4 5 6 ... 10 Next
Hello guys!
I always feel a beginner when it comes to analog things, so I need help with this sensitive topic.  :)

So, I need to design an LNA for a piezoelectric hydrophone to later digitize the signal with a single-ended ADC (the ADC of my STM32 for now). Hydrophone works both in TX and RX modes (it's for a sonar).

Antenna properties: operating at ~240 kHz, nothing else is known about it now.
Specs for the amplifier are: input voltage is expected to be in the order of 10's of uVolts, so I need ~10^5 voltage gain. Double-pole bandpass frequency response centered at 240 kHz with Q~10 is probably OK as it will be later processed  with DSP. Also I want to digitally(from an MCU) control its gain in, at least, 20 dB range or so.
Also this thing is going to be installed not far from noisy things like a lot of DC-DC converters for powerful LEDs.

I intend to make it with high frequency opamps. For the gain-control part I will probably use some digital potentiometer between gain stages(or is there a better choise?). Also i can design the active filter part myself.

When it comes to the first stage of the amplifier, I am not sure what to do. I am considering two options:
1. I am not experienced with noise-sensitive things, but I guess that the common mode rejection ratio mentioned everywhere is an important part in this device to suppress common noise at inputs. I could make the first stage with a transformer(to serve as unbalanced->balanced converter) followed by a low noise high speed opamp, like one of these: AD8646, AD8651, AD8655 or OP37. But I am not sure about CMRR of a transformer, especially if it will be hand-wound on some ferrite ring. How high can it be?

2. Another option is to eliminate the transformer and take a nice instrumentation amplifier like INA128 or INA2128. One more cool instr. amp. I found is AD8231, more noisy but hey, it has digitally-programmable gain.

One more piece of advice I have seen in the Internet is to go fully differential from input to ADC (Once I had a look at a professional Imagenex sonar board, and they did exactly that with fully-differential opamps :)). But I am not sure how much sense it makes in my case if I am using a single-ended ADC.

Also one more general thing I would like to clarify about opamp circuit design is this: if I only care about high frequency part of spectrum, should I care much about opamp specs like offset voltage and input current? As I understand it makes huge difference only if I were to amplify DC signals.

Thanks to anyone who has made it through this wall of text!
General Chat / Re: "Flat Earthers"... what the F%$# !!!
« Last post by drussell on Today at 11:22:59 pm »
The newest movement is fuel hoax for airplanes.
Hoaxter discussion

LOL...  I like how he puts it:

"I never believed that so many people would find such a stupid idea so appealing, and they appear to have made themselves absolutely immune to the facts.  Just amazing!  They've got a perfect hard shell of ignorance around their, their very being."
Metrology / Re: USA calibration club (transit environmental logging?)
« Last post by rhb on Today at 11:21:01 pm »
I read back a few pages but didn't see any references to logging temperature during transit.   After hunting for a paper by Franco Rota on the noise diode sources he built for the 13th EME conference without success last night, I'm a bit annoyed with google.  I *know* I have a copy, but no idea where.

Is that being done?  If not, the MSP430 typically has an internal temperature sensor. So it would be dead simple to build a battery powered data logger that just rode around with a reference and logged the ambient temperature.  Not much more effort to log BP and RH.  Probably more work to select the sensors.  If the container is insulated, one would need only a few measurements per hour, so battery life would be very long as in months or years.
Buy/Sell/Wanted / Re: FS: (US) Lecroy 9354AL 4ch 500MHz 2GS/s 8MPt
« Last post by coromonadalix on Today at 11:12:54 pm »
service manual : 

Would be nice to pop an lcd in it ;)
I'm also forgetting it's some kind of flyback trans, and I should see what my MS5803 LCR meter thinks of it
Buy/Sell/Wanted / Re: Selling two oscilloscopes
« Last post by coromonadalix on Today at 11:05:59 pm »
the tek 224 is a 60 mhz scope  you have an typo error ... 1 mhz ??

Isolated Channel Architecture
Floatable to ±850 V/channel (224)
60 MHz (224)
100-ns Glitch Capture
6-kV Peak Surge Rating
Video Line Trigger
Save Reference Memory
Dual 10-MS/s Digitizers
Programmable through RS-232-C
Save Setup
Test Equipment / Re: Extech EX430 missing part
« Last post by ElektroQuark on Today at 11:02:38 pm »
There are some marks in the "socket" that looks like there was one.
Projects, Designs, and Technical Stuff / Strange optocoupler behavior
« Last post by atgeek on Today at 11:01:52 pm »
I'm using 4 optocoupler for switch some relay with an attiny85. Each optocoupler is connected with a 150 ohm resistor to the attiny gpio. I've noticed that I had left the ground unconnected on the optocouplers anode but surprisingly they works the same , turning on the relay. How is it possible? Maybe due to some capacitance beetwen the anode and the emitter?
Projects, Designs, and Technical Stuff / Re: Prototyping RF shielding
« Last post by noname4me on Today at 11:01:23 pm »
Kitchen foil and aluminium roofing tape (make sure it is conductive both sides).

I've had good results using that to shield an enclosure at up to 30V/m field strength at spot frequencies in the ISM band and 10V/m throughout 80 MHz to 1GHz (it works beyond this too, just didn't need to test it beyond this for compliance)

This is good to prototype if you are looking to do it on the cheap and just need something to work at the time.

Sent from my SM-G935F using Tapatalk

Crowd Funded Projects / Re: myuArt - A UART converter finally done right
« Last post by pylo on Today at 10:55:26 pm »
On the topic of a case: yeah best would be to have one too, but the options are:
  • Let a case of my own be manufactured. Too expensive below 10.000pcs, so not an option.
  • Design into an existing case. This would still need to be modified with cutouts for cables and windows for LEDs plus printing for labels. Also, the board is pretty small, so a standard case would make it a lot bulkier (and uglier).
  • Design and 3D-print the case myself. First, I have no experience with mechanical design, and second I don't have a 3D printer.
  • Ask for help in design, and share the design so that anybody can print their own case. This is not so bad, but most people still don't have a 3D printer, so only a few would be able to benefit from this solution.
  • Apply heatshrink. Might not be "professional", but TBH it works, it is cheap, and is available for everybody. And as already pointed out, not so ugly as long as transparent.
  • Apply conformal coating to the board. I think this could be workable as far as costs are concerned (though not so sure as it would require a 2-phase assembly), however, this is far too unreliable (abresion, thickness etc.), so I call my veto on this.

Summarizing, only heatshrinking works that I can readily ship to my backers. Having a public design for a custom 3D-printed case would be ultra-cool, but people would need to print it themselves. EDIT: Or, have a backer tier during the campaign where a printed case is included, but sold at a higher price.
Pages: [1] 2 3 4 5 6 ... 10 Next