gain control for 100Mhz - Page 1
Forum section: electronics / beginners

author: navidrct
author_rank: Regular Contributor
timestamp: October 12, 2015, 06:17:01 am
content: hii build a function gen that its output frequency is about 100 MHzi want the amplitude of wave be variablemaybe i use gain control but its expensivei want something cheap.anybody know a way?

author: JoeB83
author_rank: Regular Contributor
timestamp: October 12, 2015, 06:22:35 am
content: I think we need more information about your project in order to help you.

author: navidrct
author_rank: Regular Contributor
timestamp: October 12, 2015, 06:32:50 am
content: Quote from: JoeB83 on October 12, 2015, 06:22:35 am100 MHz . a lot of wave type . output must be between 12 and -12 .u think of sine wave that its swing between -5 and 5notice that i have -12 and 12 by power supply .

author: JoeB83
author_rank: Regular Contributor
timestamp: October 12, 2015, 06:48:26 am
content: Can you share a schematic?

author: navidrct
author_rank: Regular Contributor
timestamp: October 12, 2015, 06:51:10 am
content: Quote from: JoeB83 on October 12, 2015, 06:48:26 amit does not matteri have 100MHz wave that i want be variable.do u know a way that its cheap?

author: vk6zgo
author_rank: Super Contributor
timestamp: October 12, 2015, 07:03:51 am
content: PIN diode.http://www.radio-electronics.com/info/rf-technology-design/attenuators/rf-variable-pin-diode-attenuator.php

author: navidrct
author_rank: Regular Contributor
timestamp: October 12, 2015, 07:14:59 am
content: Quote from: vk6zgo on October 12, 2015, 07:03:51 ami don't think that it will be good solution for function gen that has 100 MHz bandwidth

author: tggzzz
author_rank: Super Contributor
timestamp: October 12, 2015, 07:44:12 am
content: Quote from: navidrct on October 12, 2015, 06:51:10 amYes it does matter.Yes I do know a way that meets your very vague requirements.You would be well advised not to tell people that know about these things that the answers to their questions do not matter.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 12, 2015, 07:49:04 am
content: Quote from: navidrct on October 12, 2015, 07:14:59 amI'm not saying to use that exact design,but PIN diode circuits are widely used as attenuators.One I've worked on was at 433MHz.In his original post,hedidsay 100MHz signal,not bandwidth.OK,I should have realised what he meant when he said "function generator".

author: Fungus
author_rank: Super Contributor
timestamp: October 12, 2015, 08:08:15 am
content: Quote from: navidrct on October 12, 2015, 06:51:10 amPotentiometer?

author: tron9000
author_rank: Frequent Contributor
timestamp: October 12, 2015, 08:30:01 am
content: Quote from: navidrct on October 12, 2015, 06:51:10 am+1 tggzzz,No Schematic, no dice -http://tron9000.blogspot.co.uk/2015/05/its-all-in-your-head.html

author: daqq
author_rank: Super Contributor
timestamp: October 12, 2015, 08:36:45 am
content: QuoteDefine cheap. The cheapest way is to simply scale your DAC input data and trade amplitude control for loss of resolution. Depending on your DAC input type you can scale the input (reference) voltage. Variable gain amplifiers are another option. Attenuators (relay based, solid state) can get pricey, but you can scale without resolution loss over several decades when done properly.

author: navidrct
author_rank: Regular Contributor
timestamp: October 12, 2015, 08:43:31 am
content: my DAC output full range is 30mAin attachment u can see

author: oldway
author_rank: Super Contributor
timestamp: October 12, 2015, 09:20:58 am
content: It seems to me that what you need is an adjustable 50R output amplifier for your function generator.

author: tggzzz
author_rank: Super Contributor
timestamp: October 12, 2015, 09:45:54 am
content: Your spec keeps on changing.First it is 100MHz, then 100MHz bandwidth, and I suspect even that isn't correct (it certainly isn't accurate).First it is single-ended voltage, then you introduce differential current.You should do research on "differential transimpedance" and "reconstruction filter".

author: tggzzz
author_rank: Super Contributor
timestamp: October 12, 2015, 10:04:47 am
content: Quote from: tron9000 on October 12, 2015, 08:30:01 amMy variant ishttps://entertaininghacks.wordpress.com/library-2/good-questions-pique-our-interest-and-dont-waste-our-time-2/I encourage the OP to understand what's in it.

author: navidrct
author_rank: Regular Contributor
timestamp: October 12, 2015, 10:34:28 am
content: Quote from: oldway on October 12, 2015, 09:20:58 amu mean digital resistor?if yesthat wont work cause that cant support 100 MHz

author: KJDS
author_rank: Super Contributor
timestamp: October 12, 2015, 10:54:22 am
content: Quote from: navidrct on October 12, 2015, 10:48:00 amWhat makes you think that a suggestion of an adjustable amplifier can mean a digital resistor?

author: navidrct
author_rank: Regular Contributor
timestamp: October 12, 2015, 10:56:42 am
content: Quote from: tggzzz on October 12, 2015, 09:45:54 amsorry sorry that was my mistakemax freq is 100MHz

author: navidrct
author_rank: Regular Contributor
timestamp: October 12, 2015, 10:59:06 am
content: Quote from: KJDS on October 12, 2015, 10:54:22 amthen you mean voltage gain control that i said before its so expensive

author: daqq
author_rank: Super Contributor
timestamp: October 12, 2015, 11:30:43 am
content: QuoteOK, could you please define expensive? 1 USD? 3 USD? 5 USD? 10 USD? 20 USD?

author: Fungus
author_rank: Super Contributor
timestamp: October 12, 2015, 11:35:20 am
content: Quote from: navidrct on October 12, 2015, 10:59:06 amYou want a 100MHz amplifier that isn't expensive?You'redoing it wrong. But we have no idea what you're actually doing so we can't help.I declare this thread finished until you provide a schematic.

author: navidrct
author_rank: Regular Contributor
timestamp: October 12, 2015, 12:17:07 pm
content: Quote from: Fungus on October 12, 2015, 11:35:20 ami want variable voltage control amplifier not just an amplifier

author: oldway
author_rank: Super Contributor
timestamp: October 12, 2015, 12:24:20 pm
content: Please post in the beginner section, you seems to be a beginner.

author: oldway
author_rank: Super Contributor
timestamp: October 12, 2015, 12:26:50 pm
content: Quote from: navidrct on October 12, 2015, 10:34:28 amDid you ever look at a schematic of a function generator ?

author: navidrct
author_rank: Regular Contributor
timestamp: October 12, 2015, 12:28:55 pm
content: Quote from: daqq on October 12, 2015, 11:30:43 amin my country a VGC is about 15 US . in large scale it is expensive

author: navidrct
author_rank: Regular Contributor
timestamp: October 12, 2015, 12:31:18 pm
content: Quote from: oldway on October 12, 2015, 12:26:50 pmyes . i have Agilent schematic of a function generator that its so old and complicateddo u have any useful?

author: navidrct
author_rank: Regular Contributor
timestamp: October 12, 2015, 12:33:12 pm
content: Quote from: oldway on October 12, 2015, 12:24:20 pmGooooood for U that ur not beginner

author: oldway
author_rank: Super Contributor
timestamp: October 12, 2015, 12:35:23 pm
content: You make everybody crazy here because you ever can't especificate what you want !

author: Fungus
author_rank: Super Contributor
timestamp: October 12, 2015, 12:41:26 pm
content: Quote from: navidrct on October 12, 2015, 12:17:07 pmVariable voltage control ofWHAT?PS:yourself

author: oldway
author_rank: Super Contributor
timestamp: October 12, 2015, 12:42:41 pm
content: QuoteTo amplifier a 100Mhz square wave, you need at least 10 times greater bandwith, that's a 1 Ghz bandwith amplifier...Doe you think it is not a complicated amplifier ?

author: oldway
author_rank: Super Contributor
timestamp: October 12, 2015, 12:51:50 pm
content: Quote from: navidrct on October 12, 2015, 12:28:55 pmYou intend to produce something in large scale ?...You are kidding...

author: tggzzz
author_rank: Super Contributor
timestamp: October 12, 2015, 01:41:38 pm
content: Quote from: navidrct on October 12, 2015, 12:28:55 pmWhy don't youspecifyyour country?My guess is that you think function generators are unnecessarily expensive, and that you can make cheaper ones. For that to be true one of two preconditions must be valid:you have a secret technical innovation that nobody else has thought of. Given your question, I doubt thatverymuchyou can design, procure, make, test, sell, distribute, and all the otherbusinessactivities cheaper than other people. Why do you think that other people aren't already doing that?You should research the "Dunning Krueger effect".

author: Fungus
author_rank: Super Contributor
timestamp: October 12, 2015, 01:49:42 pm
content: Here's a circuit I found on the web. I think it will do what you're looking for. All you need is a cheap potentiometer:

author: navidrct
author_rank: Regular Contributor
timestamp: October 12, 2015, 02:14:17 pm
content: Quote from: Fungus on October 12, 2015, 01:49:42 pmthat was everything i need . thanks . plz don't hurt ur brain to much

author: navidrct
author_rank: Regular Contributor
timestamp: October 12, 2015, 02:17:16 pm
content: i think i found a solution .that was interesting that what Agilent do in its function gen .harder for software but cheaper in hardware

author: navidrct
author_rank: Regular Contributor
timestamp: October 12, 2015, 02:26:14 pm
content: Quote from: tggzzz on October 12, 2015, 01:41:38 pmthanksbut i did it in 100 MHz output in cheap way with right choose .Agilent in function gen of old time has a method that is so cheap that i want to usevariable part of circuit was issue for being cheapi will use it and i will show the result

author: tron9000
author_rank: Frequent Contributor
timestamp: October 12, 2015, 03:14:57 pm
content: Quote from: navidrct on October 12, 2015, 02:14:17 pmWHAT? A bloody POT! Here's me getting all...and all he needed was a flipping POT!Worse than the ending to Revolver!

author: AF6LJ
author_rank: Unknown
timestamp: October 12, 2015, 03:18:43 pm
content: Quote from: tron9000 on October 12, 2015, 03:14:57 pmThat wouldn't work very well anyway.Apparently the output flatness over frequency is not important to the designer of this FG.There is no "cheap way" to have uniform output amplitude over a wide frequency range at those frequencies without an auto-leveling circuit.

author: Fungus
author_rank: Super Contributor
timestamp: October 12, 2015, 05:45:24 pm
content: Quote from: navidrct on October 12, 2015, 02:14:17 pmNo problem!

author: navidrct
author_rank: Regular Contributor
timestamp: October 12, 2015, 05:53:35 pm
content: Quote from: tron9000 on October 12, 2015, 03:14:57 pmU killing me

author: SaabFAN
author_rank: Frequent Contributor
timestamp: October 12, 2015, 06:29:27 pm
content: My solution:J-FET Attenuator controlled by a OpAmp that is fed with the voltage from a Peak Detector and one from a DAC. After that a simple AB-Class amplifier powered by +/-15V with the Peak-Detector connected to its output.

author: AF6LJ
author_rank: Unknown
timestamp: October 12, 2015, 06:36:26 pm
content: Quote from: SaabFAN on October 12, 2015, 06:29:27 pmI would do simething similar but without the DAC.

author: JoeB83
author_rank: Regular Contributor
timestamp: October 12, 2015, 08:53:32 pm
content: navidrct: Next time you ask for help please provide a schematic and try being a little less rude. This kind of shit won't fly in the real world.

author: navidrct
author_rank: Regular Contributor
timestamp: October 12, 2015, 08:59:30 pm
content: Quote from: JoeB83 on October 12, 2015, 08:53:32 pmI had a simple question not a rocket scienceSorry but most of people here just mask fun of every word without any help.If somebody think that I'm giving information less than usual can ignore topic.Please if u don't get the topic just ignore pleaseSent from my HUAWEI G730-U00 using Tapatalk

author: tggzzz
author_rank: Super Contributor
timestamp: October 12, 2015, 09:32:17 pm
content: Quote from: navidrct on October 12, 2015, 08:59:30 pmEven simple questions need to be approached and asked in appropriate ways.Andwedo "get the topic", butyoudon't!

author: AF6LJ
author_rank: Unknown
timestamp: October 12, 2015, 09:54:14 pm
content: Quote from: navidrct on October 12, 2015, 08:59:30 pmWe get the topic; the problem is lack of information.No we don't need a schematic, but more information would be helpful.Is this function generator operating from DC-100MHZ?designing an output leveling circuit is not such an easy task, how are you going to compensate for frequency change?how about compensating for wave shape?Are you going to be driving a 50 ohm load?We really cannot be very helpful without more information.

author: navidrct
author_rank: Regular Contributor
timestamp: October 12, 2015, 09:58:01 pm
content: Quote from: AF6LJ on October 12, 2015, 09:54:14 pmThanksI'm gonna use agilent way for that .Hope it workSent from my HUAWEI G730-U00 using Tapatalk

author: KJDS
author_rank: Super Contributor
timestamp: October 12, 2015, 10:04:01 pm
content: Quote from: navidrct on October 12, 2015, 09:58:01 pmHave you worked out yet why we need more information in order to provide a good answer?Which agilent schematic are you using? It's probable that it could be simplified for your purpose, it's also very likely that there will be some subtleties in any design that will provide flat variable gain from DC to 100MHz that aren't obvious.

author: DimitriP
author_rank: Super Contributor
timestamp: October 13, 2015, 01:07:42 am
content: You be not now a lot I found myself annoyJesus christ!!

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: October 13, 2015, 01:19:28 am
content: Hi,If you have a DAC in your function generator, have you considered varying the reference voltage to the DAC?This is a DC voltage and therefore much easier to deal with.You can put a small DAC between the reference and the reference input to the main DAC to control amplitude.Jay_Diddy_B

author: Fungus
author_rank: Super Contributor
timestamp: October 13, 2015, 06:30:29 am
content: Quote from: Jay_Diddy_B on October 13, 2015, 01:19:28 amDoes he? That's the first mystery...

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 13, 2015, 07:07:14 am
content: Quote from: navidrct on October 12, 2015, 12:28:55 pmgood luck! i have an amplifier, err an opamp as an output stage in my FG, in that price range, just an opamp, no variable control nada...Quote from: navidrct on October 12, 2015, 02:14:17 pmgood luck! on not hurting your brain putting that in your 100MHz FG for the masses...

author: tggzzz
author_rank: Super Contributor
timestamp: October 13, 2015, 08:04:24 am
content: Quote from: Fungus on October 13, 2015, 06:30:29 amWe did eventually manage to squeeze apartialschematic out of him, and it showed a differential current source. So a DAC is a good guess.

author: navidrct
author_rank: Regular Contributor
timestamp: October 13, 2015, 08:09:29 am
content: Quote from: Jay_Diddy_B on October 13, 2015, 01:19:28 amMy DAC have feedback but our purpose now is that don't use thatSent from my HUAWEI G730-U00 using Tapatalk

author: navidrct
author_rank: Regular Contributor
timestamp: October 13, 2015, 08:14:39 am
content: Quote from: tggzzz on October 13, 2015, 08:04:24 amI'm new in forum thing . SorryI'll do my best . ThanksSent from my HUAWEI G730-U00 using Tapatalk

author: tggzzz
author_rank: Super Contributor
timestamp: October 13, 2015, 08:45:06 am
content: Quote from: navidrct on October 13, 2015, 08:14:39 amMaking mistakes is inevitable; wealldo it. As I taught my daughter, "let's makenewmistakes".Understanding and applying what's inhttps://entertaininghacks.wordpress.com/library-2/good-questions-pique-our-interest-and-dont-waste-our-time-2/is relevant to more thna this forum; it is valuable in alll aspects all of life.

author: navidrct
author_rank: Regular Contributor
timestamp: October 13, 2015, 11:49:28 am
content: Quote from: tggzzz on October 13, 2015, 08:45:06 amThanksSent from my HUAWEI G730-U00 using Tapatalk

author: krish2487
author_rank: Frequent Contributor
timestamp: October 13, 2015, 01:36:41 pm
content: I am guessing he is not a native english speaker...Therein is a part of the problem.This can be addressedThe other being, lack of clarity on what,how,why he wants help with...This part will need a certain introspection on his part and clear framing of answers to those questions.I, myself, am not a native english speaker and I find that writing down on a piece of paper helps me articulate better.

author: tggzzz
author_rank: Super Contributor
timestamp: October 13, 2015, 01:51:58 pm
content: Quote from: krish2487 on October 13, 2015, 01:36:41 pmI - as an English speaker - find that writing down the problem, approaches, solutions, unknowns helps me averygreat deal. Often to the extent that I'm able to answer my own question without bothering other people.Of course, it does help if you know what to write down, i.e. have a clue about how to approach problem definition and problem exploration and problem solving.

author: krish2487
author_rank: Frequent Contributor
timestamp: October 13, 2015, 01:53:37 pm
content: Touche!! :-) critical thinking and problem solving abilities are the missing part of the equation. I just did not think of them first.Sent from my GT-I9300 using Tapatalk

author: navidrct
author_rank: Regular Contributor
timestamp: October 13, 2015, 03:55:55 pm
content: Let's create topic for that. What feedback resistor do u suggest?Sent from my HUAWEI G730-U00 using Tapatalk