How to make simple buffer/amplifier for sqare wave signal ??? - Page 1
Forum section: electronics / projects

author: gabri.peic
author_rank: Regular Contributor
timestamp: April 05, 2022, 02:50:53 pm
content: Hi. I am playing around with analog tone generators, And i have a situation where i have sqare wave signal that goes through some circuitry (diode keyers) that makes its output impedance really high.So i need some sort of preamp/buffer that would take that high impedance signal and put out identical signal but with more current to be able to go through some filters and drive normal line level inputs.I was thinking of simply using one transistor that would be turned on by the sqare wave output, But i don't know how well that would work.Any ideas anyone

author: rstofer
author_rank: Super Contributor
timestamp: April 05, 2022, 03:07:35 pm
content: Sounds like a job for an op amp voltage follower given there don't seem to be other constraints,https://www.allaboutcircuits.com/video-tutorials/op-amp-applications-voltage-follower/

author: PKTKS
author_rank: Super Contributor
timestamp: April 05, 2022, 03:12:41 pm
content: yep sounds piece of cake...Just put a power inverter switching in front of it...Paul

author: MarkF
author_rank: Super Contributor
timestamp: April 05, 2022, 03:23:34 pm
content: What are the voltage level? Maybe I'm totally off base here.If TTL, you could use a SN74AC14 Schmitt Trigger Inverter as Alan did in his TDR.Just bypass the oscillator front end and feed in your square wave (i.e. remove jumper J1 in my circuit).

author: gabri.peic
author_rank: Regular Contributor
timestamp: April 05, 2022, 03:39:11 pm
content: Thanks for the response everyone.The voltage follower approach seems like a good option so i will look into it.As far as the voltage levels. Well nothing is finalized yet but output of the keying circuit is around 12v dc

author: TimFox
author_rank: Super Contributor
timestamp: April 05, 2022, 03:44:52 pm
content: If the voltage levels for the square wave are variable and important, then you need an amplifier, such as a voltage follower (op amp or transistor). The requirements on such an amplifier include the rise time and gain accuracy.If the voltage levels are fixed, but the timing is important, then a digital implementation is simpler (logic gate buffer).

author: gabri.peic
author_rank: Regular Contributor
timestamp: April 05, 2022, 04:03:10 pm
content: Quote from: TimFox on April 05, 2022, 03:44:52 pmWell the voltage out of the oscilators is fixed but the diode keying circuit has a "soft attack" that basically charges a capacitor when i press the key and slowly applies voltage to the diode causing the sqare wave to come in slowly like someone is turning up the volume knob across 1 or 2 seconds, and when the key is released the cap discharges and the signal slowly goes away.So yeah the voltage is variable.

author: TimFox
author_rank: Super Contributor
timestamp: April 05, 2022, 04:09:26 pm
content: Your square wave signal, therefore, has relatively slow rise and fall times, and these are important to your application.A simple op-amp voltage follower should suffice: be careful that the input voltage range (0 to 12 V, or whatever) falls within the capability of the amplifier. To work well near 0 V, it is a good idea for the voltage power supply to the opamp to go at least a few volts negative, and it must go sufficiently positive to support the maximum output voltage.

author: gabri.peic
author_rank: Regular Contributor
timestamp: April 05, 2022, 04:27:56 pm
content: Quote from: TimFox on April 05, 2022, 04:09:26 pmThanks. I will probably be able to supply the op amp with both positiv and negative rails no problem since some other things will require dual rail anyway.

author: SiliconWizard
author_rank: Super Contributor
timestamp: April 05, 2022, 04:41:39 pm
content: Since you're apparently going to filter this square wave signal anyway, I suppose you're not looking to keep extremely short rise and fall times - so indeed a simple amplifier (as an opamp) with just adequate bandwidth would be the easiest fit here.