Post by thread:Re: [EE] : amplifier using hex inverter ??

> have anybody heard anything about amplifier circuit using hex > inverter chip and other discrete ? where can i find more info ? > thanks in advance You need to use a feedback resistor (from output to input) of a meg or two, to get the inverter into its linear region. They can be quite sensitive and a bit "twitchy" -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body

> -----Original Message----- > From: Jinx [SMTP:joecolquittKILLspamCLEAR.NET.NZ] > Sent: Friday, January 05, 2001 12:32 PM > To: .....PICLISTKILLspam.....MITVMA.MIT.EDU > Subject: Re: [EE] : amplifier using hex inverter ?? > > > have anybody heard anything about amplifier circuit using hex > > inverter chip and other discrete ? where can i find more info ? > > thanks in advance > > You need to use a feedback resistor (from output to input) of a > meg or two, to get the inverter into its linear region. They can be > quite sensitive and a bit "twitchy" > Performance is definately not in the upper class of amplifier design, and my experience with these designs has been the same as Jinx's. Sometimes they work fine, sometimes not. ISTR you had to use the unbuffered gates if you are using the 4000 series. The buffered ones never worked well. With LM324 type op-amps costing pennies, I don't really see the need to use logic gates other than out of curiosity. Mike -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email EraseMElistservspam_OUTTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

> > have anybody heard anything about amplifier circuit using hex > > inverter chip and other discrete ? where can i find more info ? > > thanks in advance > > You need to use a feedback resistor (from output to input) of a > meg or two, to get the inverter into its linear region. They can be > quite sensitive and a bit "twitchy" That's for CMOS. TTL will (I think) be in the mid-hundreds of ohms. I should qualify the "twitchy". With the limited experience I've had with inverters as amps, I didn't expect op-amp flexibilty. However, the use I had was quite a simple, narrow one for a specific signal and it was quite easy to fall outside of the linear range and lose output or severe clip it -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

> Sometimes they work fine, sometimes not Something else to consider is repeatability. Chips with the same part number but from different manufacturers do not always work the same. For example a Texas 4069 may not work in a circuit although a Philips 4069 might. Just a guess, but linear applications may show up differences even more -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email @spam@listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

Using digital chips as linear devices is best left to using them as oscillators in microprocessors. You will find that almost every micro has a single gate set up for exactly this use. trying to use them as general purpose linear devices is almost bound to produce tears of frustration as there is no temperature stabilization in the linear region, and no characterization of gain. It may even be that various characteristics of the active devices are chosen limit the ability to operate in the linear region, except where the gate is being built in as an oscillator. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email KILLspamlistservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

> > have anybody heard anything about amplifier circuit using hex > > inverter chip and other discrete ? where can i find more info ? > > thanks in advance > > You need to use a feedback resistor (from output to input) of a > meg or two, to get the inverter into its linear region. They can be > quite sensitive and a bit "twitchy" It also has to be a CMOS inverter, which is really an amplifier with a gain somewhat less then -1. TTL and other logic families won't work. And of course don't use a schmidt trigger. ***************************************************************** Olin Lathrop, embedded systems consultant in Devens Massachusetts (978) 772-3129, RemoveMEolinTakeThisOuTembedinc.com, http://www.embedinc.com -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spamBeGonelistservspamBeGonemitvma.mit.edu with SET PICList DIGEST in the body

>It also has to be a CMOS inverter, which is really an amplifier with a gain >somewhat less then -1. TTL and other logic families won't work. And of >course don't use a schmidt trigger. People did use to use TTL inverters for oscillators, but they do require lower value resistors than CMOS. I do remember seeing an article in an English magazine called Wireless World (this would have been in the 1970's) by someone who made a multi input audio mixer from a multiple input TTL gate. It is do-able, but not worth the effort. I agree a schmitt trigger gate will not work. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email TakeThisOuTlistservEraseMEspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

Hi Ckchan, The Application Note AN-88 from National Semiconductor (Logic Databook 1984) explain how to use CMOS inverters in the linear region. High gains only can be obtained but CMOS inverters can be usefull as post amplifier. Ciao, Maurizio ckchan wrote: {Quote hidden}> Greetings, > > have anybody heard anything about amplifier circuit using hex inverter > chip and other discrete ? where can i find more info ? thanks in advance > ! > > regards, > ckchan > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email RemoveMElistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body -- Maurizio Viterbini Istituto di Fisica dell'Atmosfera Via Fosso del Cavaliere 100 00133 Roma Italy tel. +39 06 49934200 fax +39 06 20660291 email viterbinEraseME.....ifa.rm.cnr.it -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email EraseMElistservmitvma.mit.edu with SET PICList DIGEST in the body

At 10:18 AM 1/5/01 -0500, you wrote: >It also has to be a CMOS inverter, which is really an amplifier with a gain >somewhat less then -1. TTL and other logic families won't work. And of >course don't use a schmidt trigger. It has to be an *unbuffered* (UB) CMOS inverter to get good results, though as some have said you can sometimes use LSTTL inverters etc. for oscillators. The problem with using a buffered version is that there are internal nodes that you cannot get at in order to compensate the amplifier to get some phase margin. It can thus oscillate internally (which is a BAD thing). Actually the gain near the transition (where you bias it) is much more than 1, you can reduce it to some controlled value by using a couple of resistors. R2 x----/\/\/\/\---x C1 R1 | | 0--||--/\/\/\---x-----|>o-------x----> out Gain ~= -R2/R2 , for reasonably low values of R2/R1 Input impedance ~= R1 for Xc << R1 Vout (dc) ~= Vdd/2 (but quite variable, see the data sheets) I'd suggest only doing this with 40xx series CMOS, the Iq of the parts such as 74HC and so on may be quite high. Best regards, =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= Spehro Pefhany --"it's the network..." "The Journey is the reward" RemoveMEspeffEraseMEEraseMEinterlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com Contributions invited->The AVR-gcc FAQ is at: http://www.bluecollarlinux.com =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservspam_OUTKILLspammitvma.mit.edu with SET PICList DIGEST in the body

We (and our customers) have built several million radios using a section of 74AC02 or 74LVC02 gate as an rf amplifier in a tripler going from around 100 MHz to 300 MHz. It works great and is incredibly compact and cheap for the application, but it's definitely not for the faint of heart. It took extensive Monte Carlo simulations plus a lot of bench time to get it right so that production yields were acceptable, and every time the manufacturer does a die shrink or makes any process change, it all has to be done again. For different manufacturers, it usually requires a change in some of the biasing resistors, so a second source is possible, but requires a separate bill of materials to cover the changes to other components, not to mention all the extra testing to assure that FCC compliance hasn't been compromised. I would say that it would take many many thousands of units for the few cents savings per unit to recover the added engineering costs over using a chip that was designed to be an amplifier. > {Original Message removed}

At 07:30 PM 1/5/01 +0800, you wrote: >Greetings, > >have anybody heard anything about amplifier circuit using hex inverter >chip and other discrete ? where can i find more info ? thanks in advance As already mentioned, trying to use a digital gate as an analog device by hooking up in a basic opamp feedback arrangement probably doesn't give very good results. If all you are after is rail-to-rail outputs, then better to just go with a CMOS opamp - LMC660 or LMC6032 are cheap enough. Alternatively, I have seen ckts [don't remember where] where CMOS gates are placed "inside" the feedback loop at the output node of a regular opamp. The gates can be either inverter or noninverter - just change the +/- pin connections at the opamp to compensate. _ bipolar | \opamp o-----|+ \ | >----CMOS---+----> +-|- / gate | | |_/ | | | +---------R2------+ | R1 | gnd Why might you want to do this? To get rail-to-rail at output. Also, you can simply parallel the 6 gates in the CMOS chip and increase the output drive - probably to the 50-100 mA range. I am not sure what the slew rate of this arrangement would be however - but using newer 74ACxx chips might make it pretty fast. There is some question - raised by piclisters in the past - about current draw throught CMOS chips when running in the linear region, but personally I don't think this is really a problem. They are made to run at high speeds and drive capacitive loads, where both channels are mostly open anyways. [also, prototyping & smoke-testing are half the fun]. hope this helps, - Dan Michaels Oricom Technologies http://www.oricomtech.com ========================= -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservTakeThisOuTspammitvma.mit.edu with SET PICList DIGEST in the body