design ideas wanted to reproduce analog signal - Page 1
Forum section: electronics / projects

author: rbrockman
author_rank: Newbie
timestamp: July 24, 2013, 09:20:18 pm
content: long time lurker on the forums - and now my first post. I'm in need of some design ideas.I have an analog source signal which I need to scale in amplitude and then reproduce as a new output.The analog source signal varies from 0-5v in amplitude, and from <1Hz to 1kHz in frequency. It is generally a sine wave of varying frequency.I need to generate a new output signal based upon this source signal, replicating the frequency, but varying the gain from 0.5 to 1.5. The gain adjustment needs to be dynamically controlled from a micro-controller. 8-bits of adjustment would be enough.I've thought about using an ADC and DAC, but was hoping for a simpler solution if possible. Are there such things as programmable gain op amps?Thank you for any ideas!

author: Andreas
author_rank: Super Contributor
timestamp: July 24, 2013, 09:41:29 pm
content: Quote from: rbrockman on July 24, 2013, 09:20:18 pmYou only need a multiplying DAC feeding the input signal to the reference input.The gain is set by the DAC code.With best regardsAndreas

author: rbrockman
author_rank: Newbie
timestamp: July 24, 2013, 09:59:53 pm
content: Thanks Andreas - Let me look into that approach.I see that there are digital pots and when combined with an op amp would appear to do what I need. Good example here:http://www.analog.com/en/circuits-from-the-lab/cn0112/vc.htmlI'm looking for gain +/- unity so maybe need to scale the signal down first and then apply gain. So many ways to explore....

author: AG6QR
author_rank: Frequent Contributor
timestamp: July 24, 2013, 10:10:43 pm
content: My first thought was an AD633. Look up its data sheet. It's an analog multiplier. It could reduce the problem to one of supplying a steady DC voltage into one input to set the gain, and sending the analog signal into the other input.But even simpler is a "Multiplying DAC", as Andreas suggests. See here for an introductory discussion.http://www.analog.com/library/analogdialogue/archives/44-09/mdac.htmlSend your analog signal in as the reference voltage on the multiplying DAC, and use your microcontroller to set the gain using the digital input. You might need to scale the input or output in the analog domain to take best advantage of all the bits of the DAC.

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: July 24, 2013, 11:04:42 pm
content: LM13700.

author: fcb
author_rank: Super Contributor
timestamp: July 25, 2013, 06:53:40 pm
content: Like Electro-Irradiator says the LM13700 is great part - but it is a little tricky to use as you'll have to generate an analog control voltage. It will also need a negative rail or you'll end up with a sea of bias voltages and other stuff. It will be smooth though.If you don't mind little glitches when you change gain, I'd use an 8 pit digital pot with resistors at either ends of the part to limit things to G=0.5-1.5

author: rbrockman
author_rank: Newbie
timestamp: July 25, 2013, 07:57:49 pm
content: Thank you for all of the great ideas. I'm now moving forward with a multiplying DAC approach.

author: nctnico
author_rank: Super Contributor
timestamp: July 25, 2013, 08:28:02 pm
content: I wouldn't. A programmable gain amplifier is what you need and those are readily available from Analog devices and others.

author: poorchava
author_rank: Super Contributor
timestamp: July 26, 2013, 07:30:30 am
content: LMH6505. A bit expensive and a definite overkill, but it works