Emitter Follower + LPF Sine Convert for CD4060

The waveform of an RC + emitter follower driven by a square wave? When the sine-ness is a matter of personal judgement? I'd rather play with a simulation and tweak it until I like what I see.

What's this obsession about calculating things? Sure, you can write an equation, but then you'd have to plot it (by hand? ink on vellum?) to see if you like the waveforms... as you vary the time constant.

OK, YOU calculate it and post the resulting waveforms, as a function of various RC values. Don't neglect the full transistor behavior.

Which reminds me, you never posted your calculations that resulted in the parts values in your gate booster circuit.

ollower.

nstructional material on how to do it.

This does mention using an emitter follower as a unity gain amplifier (whic h it isn't, quite - the actual gain of an emitter-follower gain tends to be around 0.99 - complementary compound emitter followers (one NPN plus one P NP) can do better).

It also covers the Sallen-Key filter with gain, which makes for easier capa citor selection - you can buy resistors on the E96 grid, but capacitors ten d to be stocked on the E6 grid, so fine-tuning the gain to get exactly the Q you want is a lot easier than fine-tuning the capacitor ratio.

You missed the poke between your eyes ?>:-} ...Jim Thompson

-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

Den fredag den 17. januar 2014 21.52.30 UTC+1 skrev snipped-for-privacy@interquest.com:

not hand, I think I hacked up a three phase one a few years ago when some one asked a similar question here

I'll have to dig for it

-Lasse

You seem to think that adding a smilie to everything that you post somehow makes you a wit.

It doesn't.

Better being a wit than a half-wit from Tulane >:-} ...Jim Thompson

Now that *is* a half-witted response. John Larkin has let it be known that he takes being called a half-wit by Jim Thompson seriously enough to put to gether a semi-evidence-based response.

Jim-out-of-touch-with-reality-Thompson's opinions are just opinions, and no t of the kind that one can take seriously. He thinks I'm "dangerously anti- American" and took it seriously enough to report me to the FBI, who must ha ve rolled about the floor laughing.

The only people who he won't regard as half-witted are those that share his bizarre political and social ideas.

Try going for a larger frequency multiple and Don Lancasters "magic sine wave" patterns with a suitable LPF.

It probably got lost somewhere in the course of this discussion, but I was hoping to build a LP filter around a single transistor, not an op amp.

Possible, or not?

Martin King

Thanks for your kind offer. Yes I have LTSpice to run the sim.

As previously mnetioned, my idea is to create the square-to-sine filter around a transistor rather than an op amp.

Can that be made to work?

Martin King

hich it isn't, quite - the actual gain of an emitter-follower gain tends to be around 0.99 - complementary compound emitter followers (one NPN plus on e PNP) can do better).

apacitor selection - you can buy resistors on the E96 grid, but capacitors tend to be stocked on the E6 grid, so fine-tuning the gain to get exactly t he Q you want is a lot easier than fine-tuning the capacitor ratio.

was hoping to build a LP filter around a single transistor, not an op amp.

To recapitulate what I previously posted, it is possible. If you want to be particularly picky, you can use the equations for a two pole Sallen-Key fi lter with gain, as presented in the Wikipedia article, to cope with the sli ghtly less than unity gain that you get out of an emitter-follower.

You will have to deal with the one Vbe DC offset.

yep, you can easily make a 3 pole LPF from a single transistor.

input R with C to GND, then into your 2 pole Sallen-Key using the transistor.

BUT! the input R changes all your values around the transistor.

This is a 1st order lowpass driving an emitter follower:

Version 4 SHEET 1 904 680 WIRE 800 16 608 16 WIRE 608 64 608 16 WIRE 96 112 0 112 WIRE 176 112 96 112 WIRE 304 112 256 112 WIRE 400 112 304 112 WIRE 544 112 480 112 WIRE 800 160 800 16 WIRE 304 176 304 112 WIRE 608 176 608 160 WIRE 672 176 608 176 WIRE 0 192 0 112 WIRE 608 208 608 176 WIRE 0 352 0 272 WIRE 304 352 304 240 WIRE 608 352 608 288 WIRE 800 352 800 240 FLAG 304 352 0 FLAG 608 352 0 FLAG 0 352 0 FLAG 800 352 0 FLAG 672 176 OUT FLAG 96 112 IN SYMBOL res 272 96 R90 WINDOW 0 77 52 VBottom 2 WINDOW 3 88 56 VTop 2 SYMATTR InstName R1 SYMATTR Value 1K SYMBOL cap 288 176 R0 WINDOW 0 64 30 Left 2 WINDOW 3 57 63 Left 2 SYMATTR InstName C1

SYMBOL npn 544 64 R0 WINDOW 0 101 17 Left 2 WINDOW 3 79 52 Left 2 SYMATTR InstName Q1 SYMATTR Value BC547C SYMBOL res 496 96 R90 WINDOW 0 -56 51 VBottom 2 WINDOW 3 -48 53 VTop 2 SYMATTR InstName R2 SYMATTR Value 47 SYMBOL voltage 0 176 R0 WINDOW 0 28 122 Left 2 WINDOW 3 11 230 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value PULSE(0 6 1m 1u 1u 30m 60m 100) SYMBOL voltage 800 144 R0 WINDOW 0 -70 93 Left 2 WINDOW 3 -61 132 Left 2 SYMATTR InstName V2 SYMATTR Value 6 SYMBOL res 592 192 R0 WINDOW 0 -69 39 Left 2 WINDOW 3 -75 76 Left 2 SYMATTR InstName R3 SYMATTR Value 100 TEXT 136 328 Left 2 !.tran 1 TEXT 32 40 Left 2 ;SORTA SINE WAVE

That's a high beta NPN transistor, like a BCX70.

Save that text as Sorta_Sine_1.asc and open that in LT Spice. Click the run icon and probe.

Play with the various values for visual appeal.

To make it softer, more sine-like, add another RC section, as a Sallen-Key lowpass filter.

Come on, John! Surely you can do better than that! What a kludge

But it gets under your skin, so I'm successful >:-}

And that "filter" of yours is an absolutely abysmal "design". ...Jim Thompson

Your being a pathetic old fool in public doesn't bother me, but it does caution me about ever letting that happen to me.

It's a first-order lowpass that the OP can play with. He did have some sort of problem with his Multisim thing "flatlining" so I figured I'd kick him off.

What have you done lately to be helpful? You're only here to try to prop up your fragile and declining ego. It's not working.

Post something better, you sad old fool. See if you can make this into a Sallen-Key or something. Or do something with a mosfet, before I do.

Thanks John. Much appreciated. Waveform is quite good eniough.

Your sim shows a BC547, but I will try a few others on the bench.

Martin King