design an common-emitter amplifiers

How to begin: read Gray and Meyer.

no, begin then show us where you get stuck.

NT

OK that's good so far. (though your grammar/spelling are worse than mine.) I'm assuming R1 and R2 are biasing the base between the supply and ground. Now you've got to figure out at what voltage the base wants to be... and that depends some on the gain and the emitter resistor that you choose.

Will you build this circuit and test it's performance? (That's the fun part!)

George H.

Years ago I would have warmed up the iron and built this circuit, and = then=20 I'd warm up the signal generator and the scope and fiddle with it. But = now=20 it is easier, faster, and safer to use something like LTSpice and build = the=20 circuit and run a simulation. So I made a very simple circuit that does = not=20 quite meet the desired specs, but may be a starting point for the OP. It = is=20 set up to do either a transient analysis or AC sweep from 20 Hz to 200 = kHz.=20 I also added plot points for V(in)/I(v2) for input impedance, and=20 I(R2)/I(v2) for current gain. It is a simple ratio (about 80) in = transient,=20 and about 37 dB in the sweep.

You may download LTSpice at:=20

I assume this may be homework and I have not actually met the OP's=20 specifications. And there will be other components to add for a = practical=20 amplifier. Those are left as exercises for the OP.

Paul

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D LTSpice ASCII file = =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D

Version 4 SHEET 1 880 680 WIRE 208 64 -96 64 WIRE 208 96 208 64 WIRE 48 144 32 144 WIRE 96 144 48 144 WIRE 144 144 96 144 WIRE -96 160 -96 64 WIRE 32 192 32 144 WIRE 96 192 96 144 WIRE 208 208 208 192 WIRE 272 208 208 208 WIRE 288 208 272 208 WIRE 208 224 208 208 WIRE -96 336 -96 240 WIRE 32 336 32 272 WIRE 32 336 -96 336 WIRE 96 336 96 272 WIRE 96 336 32 336 WIRE 208 336 208 304 WIRE 208 336 96 336 WIRE -96 384 -96 336 FLAG -96 384 0 FLAG 48 144 in FLAG 272 208 out SYMBOL npn 144 96 R0 SYMATTR InstName Q1 SYMATTR Value 2N3904 SYMBOL res 80 176 R0 SYMATTR InstName R1 SYMATTR Value 100k SYMBOL res 192 208 R0 SYMATTR InstName R2 SYMATTR Value 1k SYMBOL voltage -96 144 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 12 SYMBOL voltage 32 176 R0 WINDOW 3 -111 181 Left 0 WINDOW 123 187 176 Left 0 WINDOW 39 -88 102 Left 0 SYMATTR InstName v2 SYMATTR Value SINE(6 1 100k 10u 0 0 100) SYMATTR Value2 AC AC 1 SYMATTR SpiceLine Rser=3D1 TEXT -74 384 Left 0 !.tran 1m startup TEXT 112 384 Left 0 !;ac oct 20 20 200k=20

in

so far fair enough. I prefer to assume an hfe of 50, you'll end up with far less sub-par circuits that way, but you can start with 100.

//

I'm not clear what you mean there. As George says, Re largely sets your Rin, along with the 2 base bias Rs.

You forgot to tell us what V gain you're after.

NT

h

gain

R1//

y

It sounds like this the the OP's first transistor amp.

But heck I'm over fifty, and just learned about the Baker clamp.

George H.

P E Schoen wrote: snip

Simulation is a GREAT tool. Everybody should know how to use it effectively. BUT It's of limited use as a synthesis tool.

I've known far too many "engineers" who were simulation wizards, but had no clue what to simulate. They couldn't design a circuit. They sure could take a step in the wrong direction and simulate it into specification...as long as the real-live parts were perfect and there were no un-accounted-for parasitics.

The original question was worded like a homework problem. Some of the discussion about the components and what they do will be instructive.

ith

t gain

=3D(R1//

ply

I missed the bit where he saved up for weeks, and bought a tr with an hfe of 40 :)

NT

I guess I'm a little older than you. My swag is always to assume 30 (20 for power devices). Fewer "phuts" if you err on the low side. ;-)

You've never seen Schottky TTL? Actually, though I've been using it for forty years, I didn't know it as a "Baker clamp".

I bet you've used the principle for years, without knowing what it's called.

I came across it thirty years ago, in early PWM drives, and thought "That's a neat idea, those diodes, I can use that".

--
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)

I always thought the classic Baker clamp used two diodes; the single-Schottky clamp used for 74S/74LS etc. is a variant that was easy to make on an IC. If you use the right glancing illumination, you can see lotsa bumps on a Schottky TTL die, those are the little platinum(?) clamps.

Logically, they're the same thing. The lower threshold of the Schottky makes the second diode unnecessary but the idea is the same; a base current bypass. A Ge diode would do the same, but would be a little harder to integrate. ;-)

Didn't know that. I wouldn't have thought they were that large, rather the same order as the metal.

I was _using_ Baker clamps in I/C designs _50_ years ago ;-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

0 for

=3D(R1//

r forty

Sure, but I had no idea what was 'inside'. It's only been since 2000 that I've been selling electronics stuff that I make to someone else. Mostly opamp things.

George H.

=A0 =A0(Richard Feynman)

Nah, It was just a few months ago that I was using a CE amp as level shifter and wondered why it took so long to turn off. I haven't been doing 'seriious' electronics for very long.

George H.

mike expounded in news:jchhpa$dup$ snipped-for-privacy@dont-email.me:

I love the convenience of LTspice myself. The measurements and charts it makes with a few mouse clicks are extremely convenient. Especially if you're sharing your work.

Heh heh heh, yep.

I once had complementary 2n2222A and 2n2907A's producing 8 watts rms in LTspice. Later when I checked the power being handled by the individual transistors the news flash was "but these are only 800mw/600mw parts!" LTspice quite glibly allowed them do do much better! In real life, I would have smelled something.

Warren

yeah, but I don't think that's what Mike was talking about.

I think Mike was talking about the idea that without a clue about how things _should_ work, a person with a simulator in hand won't be any different than a monkey at a keyboard just pecking away and hoping that it comes together by accident.

That's a little different than a simulator that doesn't properly simulate heating.

Jon Kirwan expounded in news: snipped-for-privacy@4ax.com:

Agreed and I understood his drift.

In some respects, that's how some people seem to write software-- throw in some code and stop writing when their limited unit test seems to work..

Warren

I think there are some SPICE applications that show a little flame/smoke =

icon on an overloaded component. That could be animated and combined = with=20 sound to make it more realistic. Perhaps a "smellovision" accessory = could be=20 connected to give you the complete experience, without need for face = shield!

I have also made a simulation in LTSpice that showed over unity = operation.=20 It was probably because a component contained a voltage or current = source=20 that was not visible externally and of course would not be in a real=20 component (unless it actually contained a battery).

But overall, LTSpice is an excellent tool and also a great way to share = and=20 collaborate on relatively simple designs.

I also have TINA

which has a free version from = but I have their basic version which is less than $100. It has lots of = nice=20 features, and also incorporates PCB Layout, autorouting, and 3-D views = of=20 assembled boards. But I only use it once in a while. I just recently=20 upgraded when they had a special offer. It is especially useful if you = are=20 designing with TI parts, as they have many models available.

Paul=20