Small Signal Generator AMP Circuit - Page 1
Forum section: electronics / projects

author: dreaquil
author_rank: Regular Contributor
timestamp: January 16, 2014, 09:40:59 pm
content: Hey guys,I am working on a small project. I have a picoscope 2204 (10Mhz PC based oscilloscope which has an AWG). The down side of the AWG is that it only outputs a max of 2Vp-p. Now I was thinking of making a tiny Amp PCB which I could hook up to the Female BNC and have it output through a male BNC I could hook up my probe to that if I needed a higher voltage. The problem is that I can't find myself any Male PCB BNCs. To be honest I've never seen them on a PCB before so I'm beginning to wonder they are used at all. As for the PCB I was thinking a simple LT1006 in a non inverting amp format. Does anyone have any info about the BNCs and maybe some further suggestions for my circuit? I want it to be pretty small.http://upload.wikimedia.org/wikipedia/commons/thumb/b/b9/BNC_connector_50_ohm_male.jpg/740px-BNC_connector_50_ohm_male.jpgThats the BNChttp://www.picotech.com/images/PS2200A-frontBack.jpgand thats my Picoscope

author: fcb
author_rank: Super Contributor
timestamp: January 16, 2014, 09:48:03 pm
content: I haven't seen a PCB mounted male bnc before.I'd design it with a standard PCB mount female (as per the Picoscope) and then supply it with a 'barrel'.http://uk.farnell.com/multicomp/bnc-plug-plug-adaptor-nickel/adaptor-bnc-plug-plug/dp/1169740

author: dreaquil
author_rank: Regular Contributor
timestamp: January 16, 2014, 10:00:02 pm
content: Makes sense... ye that was my second guess but I thought I'd try see if I can make it as solid as possible. Another problem came to mind .. If I'm gonna use a single supply opamp and i'm gonna supply it with a -1V to 1V sine wave... will I be losing the negative portion?

author: fcb
author_rank: Super Contributor
timestamp: January 16, 2014, 10:13:59 pm
content: If you are going to make a pucker job, you'll need to supply the op-amp with split rail supplies.

author: dreaquil
author_rank: Regular Contributor
timestamp: January 16, 2014, 10:23:48 pm
content: Sorry for the dumb question but would a high impedance voltage divider do the trick or are there more professional ways to do it? cause i want it to be as solid as can be...

author: fcb
author_rank: Super Contributor
timestamp: January 16, 2014, 11:47:54 pm
content: No free lunch - "high impedance voltage divider" would not work well.How were you planning on powering your AWG amplifier before?

author: tszaboo
author_rank: Super Contributor
timestamp: January 16, 2014, 11:56:10 pm
content: One thing I like about BNC is the cables are always male, the equipment is always female, and there are no exceptions. It makes everything compatible.Just think about the serial port cables... You have six different type.This should stay this way, any other equipment should be destroyed by any means necessary.

author: jolshefsky
author_rank: Regular Contributor
timestamp: January 17, 2014, 12:00:56 am
content: So why not just use a female board-mount BNC and a male-to-male coupler?

author: JackOfVA
author_rank: Unknown
timestamp: January 17, 2014, 12:12:04 am
content: Quote from: NANDBlog on January 16, 2014, 11:56:10 pmNot so at all. Consider an attenuator - most commonly manufactured with a female BNC on one end and a male BNC on the other so that it may be added easily to either a cable or instrument. Some special purpose amplifiers are manufactured with both the input and output being male panel mount BNC connectors, with spacing to fit female BNC connectors so they can be mounted with zero cable length.Panel mount male BNC connectors are manufactured with both a 4-hole flange mount or a single hole mount. Not always easy to find, but they do exist. I've never seen a PCB mount version, but that's not to say they don't exist.

author: dreaquil
author_rank: Regular Contributor
timestamp: January 17, 2014, 09:49:49 am
content: Quote from: fcb on January 16, 2014, 11:47:54 pmWell the AWG is powered directly from the USB port on the PC.As for splitting the supply rails, I have a step variable small DC power supply up to 24V which I'm thinkin of using, and I found the following circuit to split the rails.. For some reason the opamp is not oscillating... can't find what i'm doing wrong

author: fcb
author_rank: Super Contributor
timestamp: January 17, 2014, 10:01:12 am
content: Quote from: dreaquil on January 17, 2014, 09:49:49 amIt's not meant to....

author: dreaquil
author_rank: Regular Contributor
timestamp: January 17, 2014, 10:08:44 am
content: What do you mean? isnt it in non inverting amp conf? im giving it a sine input of 100mV which should output a gain of 11x100mv= 1.1V sine wave no?

author: fcb
author_rank: Super Contributor
timestamp: January 17, 2014, 10:24:08 am
content: 1. The amplifier is designed to amplify, you do not want it to oscillate.2. Have you actually built the circuit or just simulated it?3. Where is the grounding for the input? Is it at the pseudo centre point? Are you applying the signal across the 50R?

author: dreaquil
author_rank: Regular Contributor
timestamp: January 17, 2014, 10:28:26 am
content: sorry, I meant the output is not oscillating .. i.e i'm just getting a DC voltage at the output.I've only simulated it so far since I don't have the parts yet.The grounding is at the pseudo centre point applying it across the 50R.Edit:Nevermind .. I realised what you were trying to tell me... the sinusoidal input did not have the same ground reference.. dumb mistake on my part..

author: fcb
author_rank: Super Contributor
timestamp: January 17, 2014, 10:39:40 am
content: Possible issues? Probably something your doing wrong or missing with the sim:Looking at the DC average voltage out (which will be 0)...Incorrect connections for signal in.Incorrect output measurement (no gnd), etc...)Pin 8 (shutdown) SPICE model fault (unlikely).

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: January 17, 2014, 01:54:52 pm
content: Both male and female PC-mount BNC connectors exist. I don't know the manufacturer off the top of my head, but I do know I've got one in my parts box. I also have both male and female cables and do make use of them now and then, though obviously most equipment is standardized as you'd expect.You can roll your own midpoint voltage reference, or consider the TI "rail splitter". They work well for opamp circuits, but power circuits are a bit harder. Does this amp need to go down to DC so it can handle offsets and very low frequencies?

author: dreaquil
author_rank: Regular Contributor
timestamp: January 17, 2014, 03:32:53 pm
content: Ye it would need to go down to very low frequencies and possibly offsets... is there something i should be taking into consideration? I'll post my finished layout once ive done it.