Designing single powered TLV272 precison full wave rectifier using spice sim - Page 1
Forum section: electronics / projects

author: eneuro
author_rank: Super Contributor
timestamp: August 22, 2014, 07:21:38 pm
content: Hello,Just trying to convert this precision full wave rectifier schematics below with TL072 opamps to single powered one using TLV272 opamp and BAT85 diodes spice models.Decided to try to use simulator while I'm not sure if I add virtual ground to first opamp and AC-coupled input (I'd like to use it for peak detection and demodualtion of small AC voltage at normal frequency not higher that 20kHz at the moment) output opamp will give me nice shifted by Vcc/2 rectified input signal like in oryginal double powered version?I've found another similar precision full wave rectifier used in AM detection circuit but it uses 3 opampsTrying to find a way to modify this double powered 2 amps first circuit to achieve something similar but using 1 opamp less and try to add some gain to rectified signal.I've just downloaded TLV271 spice models, but on TI website there are 2 zip archives with files*.libextensions titled "* TINA*" and "*PSPICE*", but when tried to find any differencies between them it looks like those opamp.subcktdefinition files only differs in simulator description versions, so I can take one of them for this simulation inspiceI guess?QuoteI haveBAT85diodespicemodels too, but never usedspicesim before, so it will be a little challenge.Hopefully, I've succesfully recompiledngspiceunder Linux withgspiceuiinterface

author: void_error
author_rank: Frequent Contributor
timestamp: August 23, 2014, 06:31:49 am
content: Quote from: eneuro on August 22, 2014, 07:21:38 pmI had a project which used this and it worked just fine with a single supply. Output was the level-shifted full-wave rectified input signal. Just keep the input signal level and/or overall gain low enough so the opamp outputs don't clip.Quote from: eneuro on August 22, 2014, 07:21:38 pmI think you'll need two opamps for this. Gain can be adjusted. Details are in the articlehttp://sound.westhost.com/appnotes/an001.htm.If you want higher input impedance you need another opamp gain/buffer stage before the rectifier.

author: eneuro
author_rank: Super Contributor
timestamp: August 25, 2014, 08:56:13 pm
content: Quote from: void_error on August 23, 2014, 06:31:49 amIt is nice to know it can work in single powered opamps version tooFor the moment I've made this 2inch2 (9V battery size) single layer PCB prototype to test diffrent opamps single/double powered and see how it affects its outputQuote from: void_error on August 23, 2014, 06:31:49 amYep, In impedance critical applications probably I will have another buffer opamp and while I need output LED for POF optic fibre or laser diode with its intensity proportional to filtered demodulated signal, so in final version quad TLV274 might be used or other opamps as well, but It will be project dependent.This is research project for the moment while opamp world is full of traps, so decided makespicesimulations too and compare its results with real hardware soldered on custom PCB development board to play with those magic precison full wave rectifiers and demistify them

author: dannyf
author_rank: Super Contributor
timestamp: August 25, 2014, 09:41:26 pm
content: You don't really need specific opamp or diode models to simulate the circuit. Ant generic opamp or diode will do.

author: eneuro
author_rank: Super Contributor
timestamp: August 25, 2014, 09:58:01 pm
content: Quote from: dannyf on August 25, 2014, 09:41:26 pmI do not think so, while there are rail-to-rail opamps which behave different and so many diffrent opampsGermanium diodes are very different than generic diode-maybe it is possible to tweak its parameters to get similar specs, but I've found fast shottky more modern equivalents to germaium 1N34A and I do not plan to use germanium diode, but it was quite easy find spice models of opamps and diodes I'm interested in including those old one, to test first, so why not to use them if I've them soldered on PCB too?

author: dannyf
author_rank: Super Contributor
timestamp: August 25, 2014, 10:25:09 pm
content: R2r output doesn't come into play unless you swing close to the rail. Diodes vfwd doesn't come into unless your opamp is slew rate limited. You have none of that here.

author: eneuro
author_rank: Super Contributor
timestamp: August 26, 2014, 04:37:59 pm
content: Quote from: dannyf on August 25, 2014, 10:25:09 pmMaybe in this case it does not matter, but I want to be as close to hardware in simulation as possible and it is clear that for example those 1N4148 & BAT85 diodesspicemodels differs, so no reason not to use BAT85 model in sim and compare later what I get from PCB output with simulated oneThis difference in those diodes parameters is leads to very interesting output in this half wave rectifier when we have input RF 350kHz 100mVmax sinusOutput using 1N4148 diode below (notice scale is in uV) so oscilate at 0.5mVmax !!!Shottky barier diode BAT85 below (mV scale) and there we heve oscilations above 30mVUpdate: It was interesting to simulate famous germanium diode 1N34A used in many crystal radios, and it looks likeBAT85outperforms it !!!That is why I used to use exactspicemodels when possible...