william_teter Posted February 13, 2013 Report Share Posted February 13, 2013 I have a circuit that needs two voltage references, lets say 5v and 2.5vWhat would be the best way to ensure the lower value was exactly 1/2 the value of the higher voltage (e.g. accounting for % tolerances on the 5v voltage reference)? Temperature variances won't be too much of a concern, but if a solution accounted for it, that would be nice.I've thought of:1. Using an individual 5v and 2.5v vref IC2. Using a resistor divider using high precision resistorsI think the latter idea is a better one since two resistors are far cheaper AND will account for the 5v reference tolerances. The downside would be no current which I shouldn't need much at all of (it is the vref for a dac with microamps current specs on the pin)Just a theory question! Quote Link to comment Share on other sites More sharing options...
Hero999 Posted February 15, 2013 Report Share Posted February 15, 2013 It's impossible to say without any additional information such as a schematic or detailed description of the circuit. Quote Link to comment Share on other sites More sharing options...
william_teter Posted February 16, 2013 Author Report Share Posted February 16, 2013 This circuit takes the output of a dac (min of 0v and max of ~4.096v.. [depending on % off]) that comes in through the Y port and creates a signal used to drive a galvo amplifier. The galvo amplifier requires a balanced bipolar differential signal between -10v and 10v. In this circuit the ILDA Y + line outputs between -5v to 5v and the ILDA Y - line outputs between +5v to -5v.I think this circuit suffers from the following:-Dead zone caused by op-amp's dc offset(?)-Independent voltage references (both appear to be sourcing about 1.2mA on the vRef lines) can be off by 0.5% (and that's ignoring temperature differences!). That means the center could be shifted a full 1% off!-Off-shifted center will mean a dac step above the center value will not be the same size as a dac step below the center value of the dac on the ILDA Y+ and ILDA Y- outputs.Edit: It's kinda hard to read, but that top left voltage says 2.048V Quote Link to comment Share on other sites More sharing options...
Hero999 Posted February 17, 2013 Report Share Posted February 17, 2013 To answer the origional question. It's definitely better to use a potential divider and a 5V reference. If more current is required, a non-inverting buffer could be used to reduce he output impedance. Quote Link to comment Share on other sites More sharing options...
william_teter Posted February 18, 2013 Author Report Share Posted February 18, 2013 Fair enough. Thank you.Any ideas on how to get rid of the offset issue? I have tried multiple solutions, but this has worked the best sofar Quote Link to comment Share on other sites More sharing options...
Guest MonkeyGate Posted May 20, 2013 Report Share Posted May 20, 2013 Not really possible. You can however, build a stable 7.5v circuit and then do what you want. There is a special circuit that splits a signal exactly in half, but I can't remember what its called...maybe a splitter!! Quote Link to comment Share on other sites More sharing options...
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