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class c rf amp with bfr93a

Hi to all. I'm looking to make a small 433Mhz transmitter using bfr93's. I want to have a oscillator , followed by a small class c amp , both using bfr93. Tho oscillator will be a standard Colpits oscillator , with a SAW resonator. I'd like to attach a class c amp (followed by filtering obviously) to boost the power. I've got a spice model for the BFR93 , from NXP. What I want to know is will a simulation of this very non linear application of the bfr93 provide any usefull results at all , or will I see total junk. A LTSpice cct is attached , simulating a BFR93 as a class c amp.It's not a finished cct , so the component values are not final.I'd just like to know if the results that I get are realistic. If I built that cct , is that what I'd get.I do realise that I have not included any paracitics in the components yet. Cheers Rob

Version 4 SHEET 1 1300 1580 WIRE 48 144 -256 144 WIRE -256 192 -256 144 WIRE 48 192 48 144 WIRE -256 304 -256 272 WIRE -240 304 -256 304 WIRE -80 304 -96 304 WIRE -16 304 -80 304 WIRE -256 320 -256 304 WIRE -368 368 -496 368 WIRE -320 368 -368 368 WIRE -80 368 -80 304 WIRE -16 368 -16 304 WIRE -496 480 -496 448 WIRE -368 480 -368 448 WIRE -368 480 -496 480 WIRE -256 480 -256 416 WIRE -256 480 -368 480 WIRE -80 480 -80 432 WIRE -80 480 -256 480 WIRE -16 480 -16 448 WIRE -16 480 -80 480 WIRE 48 480 48 272 WIRE 48 480 -16 480 WIRE -368 496 -368 480 FLAG -368 496 0 SYMBOL voltage -496 352 R0 WINDOW 3 -14 181 Left 0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value SINE(0 1 433.92Meg) SYMBOL ind -272 176 R0 SYMATTR InstName L1 SYMATTR Value 470n SYMBOL res -384 352 R0 SYMATTR InstName R1 SYMATTR Value 1k SYMBOL voltage 48 176 R0 SYMATTR InstName V2 SYMATTR Value 6 SYMBOL npn2 -320 320 R0 SYMATTR InstName Q1 SYMATTR Value BFR93A SYMATTR Prefix X SYMBOL cap -176 288 R90 WINDOW 0 0 32 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName C1 SYMATTR Value 100n SYMBOL res -32 352 R0 SYMATTR InstName R2 SYMATTR Value 200 SYMBOL ind -80 288 R90 WINDOW 0 5 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName L2 SYMATTR Value 50n SYMBOL cap -96 368 R0 SYMATTR InstName C2 SYMATTR Value 2p TEXT 464 -216 Left 0 !* Filename: BFR93A_SPICE.PRM\n* BFR93A SPICE MODEL\n* PHILIPS SEMICONDUCTORS\n* Date : September 1995\n*\n* PACKAGE : SOT23 DIE MODEL : BFR91A\n* 1: COLLECTOR; 2: BASE; 3: EMITTER;\n.SUBCKT BFR93A 1 2 3\nQ1 6 5 7 7 BFR91A\n* SOT23 parasitic model\n Lb 4 5 .4n \n Le 7 8 .83n \n L1 2 4 .35n\n L2 1 6 .17n \n L3 3 8 .35n\n Ccb 4 6 71f \n Cbe 4 8 2f\n Cce 6 8 71f\n*\n* PHILIPS SEMICONDUCTORS Version: 1.0\n* Filename: BFR91A.PRM Date: Feb

1992\n*\n.MODEL BFR91A NPN\n+ IS = 1.32873E-015\n
  • BF = 1.02000E+002\n+ NF = 1.00025E+000\n
  • VAF = 5.19033E+001\n+ IKF = 8.15511E+000\n
  • ISE = 1.39029E-014\n+ NE = 1.51292E+000\n
  • BR = 1.76953E+001\n+ NR = 9.94038E-001\n
  • VAR = 3.28032E+000\n+ IKR = 1.00000E+001\n
  • ISC = 1.04297E-015\n+ NC = 1.18993E+000\n
  • RB = 1.00000E+001\n+ IRB = 1.00000E-006\n
  • RBM = 1.00000E+001\n+ RE = 7.63636E-001\n
  • RC = 9.00000E+000\n+ EG = 1.11000E+000\n
  • XTI = 3.00000E+000\n+ CJE = 2.03216E-012\n
  • VJE = 6.00000E-001\n+ MJE = 2.90076E-001\n
  • TF = 6.55790E-012\n+ XTF = 3.89752E+001\n
  • VTF = 1.09308E+001\n+ ITF = 5.21078E-001\n
  • CJC = 1.00353E-012\n+ VJC = 3.40808E-001\n
  • MJC = 1.94223E-001\n.ENDS TEXT -66 1288 Left 0 !.tran 50n
Reply to
neddie
Loading thread data ...

All I get when I try to read that file in LTSpice are tons-o-errors.

If the BRF93 is being marketed for service at UHF then the model should work -- and there seem to be the right parasitic components in the model to imply this. SPICE is all about nonlinear circuit analysis, so as long as either you're not driving the transistor into saturation, or as long as the model is taking storage effects into account, then the model should be representative.

Whether you are correctly taking all of _your_ circuit parasitics into account is your problem. I'm sure there are folks out there that can model a circuit at that frequency and build it with confidence; I'm not one of them.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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Reply to
Tim Wescott

Yup. Rob, if you publish circuits that way make sure the models are in it as well. It won't run on other people's PC unless they also have the same model.

You can drive it pretty hard but keep in mind that SPICE does not have a

*PHUT* function. On the computer you can make a virtual kilovolt-level amp with a BFR93 which then in practice will explode violently.

But yeah, one can simulate RF stuff and it tends to come out alright on the circuit board.

--
Regards, Joerg

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Reply to
Joerg

[snip]
[snip]

Of course it does... it's called a (*PHUT* :-) Macro. I use them all the time to monitor otherwise obscure failure mechanisms... like "hot electron" effects in MOS device gates. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
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Reply to
Jim Thompson

Sure you can write your own macros. But there are no native voltage limits on device. It's a classic pitfall in RF where many people think small-signal most of the time or the professors taught that: Class A amp with a resonant circuit or just a choke on the collector, works nicely in SPICE, works nicely in real life. Then the engineer does something to drop the input below cutoff for some reason, collector flies up, way past abs max ... *WHADDABAM*

--
Regards, Joerg

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Reply to
Joerg

Bad models will always be bad models. Parameters are available to handle avalanche, etc. Unfortunately many modelers fail to use them.

And bad "designers" fail to design for loss of match... high VSWR... like when we teenagers snipped police antennas ;-)

I'm usually more concerned with subtle SOA limitations in sub-micron devices. ...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     |

                   Spice is like a sports car... 
     Performance only as good as the person behind the wheel.
Reply to
Jim Thompson

s
l
l

Thanks for the help guys .Your answers have helped. I don't plan on getting huge powers , say 20mW , but keeping an eye on the max current and collector voltage may be a good idea :0) The data sheet does not have parameters for the voltage and currents that I'm looking to use , but I'm hoping that they will at least get me in to the ballpark. I'm hoping the sims will be accurate enough to guide me from there. This RF stuff is tough!! I tried to embed the spice model into the CCT , that is why it fails :

0( This is the CCT.

Version 4 SHEET 1 1300 1580 WIRE 48 144 -256 144 WIRE -256 192 -256 144 WIRE 48 192 48 144 WIRE -256 304 -256 272 WIRE -240 304 -256 304 WIRE -80 304 -96 304 WIRE -16 304 -80 304 WIRE -256 320 -256 304 WIRE -368 368 -496 368 WIRE -320 368 -368 368 WIRE -80 368 -80 304 WIRE -16 368 -16 304 WIRE -496 480 -496 448 WIRE -368 480 -368 448 WIRE -368 480 -496 480 WIRE -256 480 -256 416 WIRE -256 480 -368 480 WIRE -80 480 -80 432 WIRE -80 480 -256 480 WIRE -16 480 -16 448 WIRE -16 480 -80 480 WIRE 48 480 48 272 WIRE 48 480 -16 480 WIRE -368 496 -368 480 FLAG -368 496 0 SYMBOL voltage -496 352 R0 WINDOW 3 -14 181 Left 0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR Value SINE(0 1 433.92Meg) SYMATTR InstName V1 SYMBOL ind -272 176 R0 SYMATTR InstName L1 SYMATTR Value 470n SYMBOL res -384 352 R0 SYMATTR InstName R1 SYMATTR Value 1k SYMBOL voltage 48 176 R0 SYMATTR InstName V2 SYMATTR Value 6 SYMBOL npn2 -320 320 R0 SYMATTR InstName Q1 SYMATTR Value BFR93A SYMATTR Prefix X SYMBOL cap -176 288 R90 WINDOW 0 0 32 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName C1 SYMATTR Value 100n SYMBOL res -32 352 R0 SYMATTR InstName R2 SYMATTR Value 200 SYMBOL ind -80 288 R90 WINDOW 0 5 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName L2 SYMATTR Value 50n SYMBOL cap -96 368 R0 SYMATTR InstName C2 SYMATTR Value 2p TEXT -64 1288 Left 0 !.tran 50n

This is the MODEL file , actually sub-cct.

  • Filename: BFR93A_SPICE.PRM
  • BFR93A SPICE MODEL
  • PHILIPS SEMICONDUCTORS
  • Date : September 1995
*
  • PACKAGE : SOT23 DIE MODEL : BFR91A
  • 1: COLLECTOR; 2: BASE; 3: EMITTER; .SUBCKT BFR93A 1 2 3 Q1 6 5 7 7 BFR91A
  • SOT23 parasitic model Lb 4 5 .4n Le 7 8 .83n L1 2 4 .35n L2 1 6 .17n L3 3 8 .35n Ccb 4 6 71f Cbe 4 8 2f Cce 6 8 71f
*
  • PHILIPS SEMICONDUCTORS
Version: 1.0
  • Filename: BFR91A.PRM Date: Feb
1992
  • .MODEL BFR91A NPN
  • IS =3D 1.32873E-015
  • BF =3D 1.02000E+002
  • NF =3D 1.00025E+000
  • VAF =3D 5.19033E+001
  • IKF =3D 8.15511E+000
  • ISE =3D 1.39029E-014
  • NE =3D 1.51292E+000
  • BR =3D 1.76953E+001
  • NR =3D 9.94038E-001
  • VAR =3D 3.28032E+000
  • IKR =3D 1.00000E+001
  • ISC =3D 1.04297E-015
  • NC =3D 1.18993E+000
  • RB =3D 1.00000E+001
  • IRB =3D 1.00000E-006
  • RBM =3D 1.00000E+001
  • RE =3D 7.63636E-001
  • RC =3D 9.00000E+000
  • EG =3D 1.11000E+000
  • XTI =3D 3.00000E+000
  • CJE =3D 2.03216E-012
  • VJE =3D 6.00000E-001
  • MJE =3D 2.90076E-001
  • TF =3D 6.55790E-012
  • XTF =3D 3.89752E+001
  • VTF =3D 1.09308E+001
  • ITF =3D 5.21078E-001
  • CJC =3D 1.00353E-012
  • VJC =3D 3.40808E-001
  • MJC =3D 1.94223E-001 .ENDS
Reply to
neddie

Sorry Rob, this one errors, says "Too few nodes, version 1.0". Whatever that means.

--
Regards, Joerg

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Reply to
Joerg

"Joerg" schrieb im Newsbeitrag news: snipped-for-privacy@mid.individual.net...

Hello Rob,

There was a missing "*" at the beginning of two comment lines. Below is the corrected version. You can add the model text as a SPICE-directive to your schematic or save it in an extra file. In the ladder case you have to include the model file.

include bfr93.sub

By the way, you forgot to add 50Ohm in series to your voltage source. There is no RF voltage source with 0 Ohm resistance in the real world.

Best regards, Helmut

  • Filename: BFR93A_SPICE.PRM
  • BFR93A SPICE MODEL
  • PHILIPS SEMICONDUCTORS
  • Date : September 1995
*
  • PACKAGE : SOT23 DIE MODEL : BFR91A
  • 1: COLLECTOR; 2: BASE; 3: EMITTER; .SUBCKT BFR93A 1 2 3 Q1 6 5 7 7 BFR91A
  • SOT23 parasitic model Lb 4 5 .4n Le 7 8 .83n L1 2 4 .35n L2 1 6 .17n L3 3 8 .35n Ccb 4 6 71f Cbe 4 8 2f Cce 6 8 71f
*
  • PHILIPS SEMICONDUCTORS
Version: 1.0
  • Filename: BFR91A.PRM Date: Feb 1992
  • .MODEL BFR91A NPN
  • IS = 1.32873E-015
  • BF = 1.02000E+002
  • NF = 1.00025E+000
  • VAF = 5.19033E+001
  • IKF = 8.15511E+000
  • ISE = 1.39029E-014
  • NE = 1.51292E+000
  • BR = 1.76953E+001
  • NR = 9.94038E-001
  • VAR = 3.28032E+000
  • IKR = 1.00000E+001
  • ISC = 1.04297E-015
  • NC = 1.18993E+000
  • RB = 1.00000E+001
  • IRB = 1.00000E-006
  • RBM = 1.00000E+001
  • RE = 7.63636E-001
  • RC = 9.00000E+000
  • EG = 1.11000E+000
  • XTI = 3.00000E+000
  • CJE = 2.03216E-012
  • VJE = 6.00000E-001
  • MJE = 2.90076E-001
  • TF = 6.55790E-012
  • XTF = 3.89752E+001
  • VTF = 1.09308E+001
  • ITF = 5.21078E-001
  • CJC = 1.00353E-012
  • VJC = 3.40808E-001
  • MJC = 1.94223E-001 .ENDS

Version 4 SHEET 1 1300 1660 WIRE -256 128 -368 128 WIRE -368 160 -368 128 WIRE -256 160 -256 128 WIRE -368 272 -368 240 WIRE -256 288 -256 240 WIRE -208 288 -256 288 WIRE -128 288 -144 288 WIRE -16 288 -48 288 WIRE 32 288 -16 288 WIRE 64 288 32 288 WIRE -256 320 -256 288 WIRE -368 368 -512 368 WIRE -320 368 -368 368 WIRE -16 368 -16 288 WIRE 64 368 64 288 WIRE -512 400 -512 368 WIRE -368 400 -368 368 WIRE -512 512 -512 480 WIRE -368 512 -368 480 WIRE -368 512 -512 512 WIRE -256 512 -256 416 WIRE -256 512 -368 512 WIRE -16 512 -16 432 WIRE -16 512 -256 512 WIRE 64 512 64 448 WIRE 64 512 -16 512 WIRE -368 528 -368 512 FLAG -368 528 0 FLAG 32 288 out FLAG -368 272 0 SYMBOL voltage -512 384 R0 WINDOW 3 -14 181 Left 0 WINDOW 123 0 0 Left 0 WINDOW 39 23 97 Left 0 SYMATTR Value SINE(0 2 433.92Meg) SYMATTR SpiceLine Rser=50 SYMATTR InstName V1 SYMBOL ind -272 144 R0 SYMATTR InstName L1 SYMATTR Value 470n SYMBOL res -384 384 R0 SYMATTR InstName R1 SYMATTR Value 1k SYMBOL voltage -368 144 R0 SYMATTR InstName V2 SYMATTR Value 6 SYMBOL npn2 -320 320 R0 SYMATTR InstName Q1 SYMATTR Value BFR93A SYMATTR Prefix X SYMBOL cap -144 272 R90 WINDOW 0 0 32 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName C1 SYMATTR Value 100n SYMBOL res 48 352 R0 SYMATTR InstName R2 SYMATTR Value 200 SYMBOL ind -32 272 R90 WINDOW 0 5 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName L2 SYMATTR Value 50n SYMBOL cap -32 368 R0 SYMATTR InstName C2 SYMATTR Value 2p TEXT -520 144 Left 0 !.tran 50n

Reply to
Helmut Sennewald

Yep. Thanks, Helmut, that made it run. Rob: The BFR93 isn't a very happy camper for class C. Connect the source with a 1000pF, add a resistor in the 7K range from base to 6V, and 10ohms or so in the emitter. Then you can drive it with 100mV and get similar output but much cleaner. Just watch for DC runaway if you build it. Of course now it ain't really class C anymore.

[...] 
--
Regards, Joerg

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Reply to
Joerg

I managed to salvage the originally posted circuit. A lot of playing got it going class C, about 50mW output into Rob's 200 ohm load (why 200 ohm?). FFT shows second harmonic -20dB, higher orders decreasing like they should. I had to rehash Rob's coupling network to step up 200 ohms to about 700 at the collector. That resulted in some stupidly small capacitance values, like 0.18pF, in order to get a decent Q of about 10. It needs a couple of volts RMS from a 50 ohm source to drive it. Dissipation in the BFR93A is around 25mW. As you say, not a happy camper for Class C.

I'll maybe have a play with simulating transmission line coupling, (microstrip?). That might appeal to your parsimonious nature .

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

So unless you I misunderstand you drive at 80mW to get 50mW out? I'd do that with three resistors instead of a BFR93A ...

And I'd think about replacing the BFR93A since it is over 10c a pop. A BFS17A can be had for 3c less. Ok, a bit less than half the ft but that ought to do here. Maybe a grounded base architecture.

--
Regards, Joerg

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Reply to
Joerg

Sorry, I wasn't clear. I didn't match the source. Input is 370 +j76 (I overcompensated the input capacitance) It actually takes about 11mW drive Still goddamn poor at about 6dB power gain. It will do over 100mW with more or less the same drive, just with a change in loading. Maybe could squeeze it as far as 10dB, if I were interested enough. It's a non-starter anyway, those capacitance values are silly.

Sounds reasonable. The OP said BFR93A, so that's what I played with. I'd instinctively go for grounded base and microstrip for the flea power he wants.

Sunday's exercise might be to compare the (Philips) model's S-parameters against Philips' data sheet values. Wanna bet they don't match?

Shame LTSpice won't do polar plots. Since it does impedance and S-params, it really ought to.

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

Pretty close match, apart from S22, which doesn't show the pronounced kink shown in the datasheet.

Found a way round that. Set LTSpice to do ASCII rawfiles, run, edit two or three LT-specific lines out of the rawfile, and load it into Berkeley Spice 3f4's Nutmeg, then plot polar and Smith from there. Much easier than trying to get LTSpice netlists to run in 3f4.

I still think the facility should be in LTSpice, though.

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

I think Jim Thompson once mentioned a software that could render raw data into all sorts of graphics including polar. Jim?

--
Regards, Joerg

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Reply to
Joerg

Scratching head... I don't remember :-( ...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     |

                   Spice is like a sports car... 
     Performance only as good as the person behind the wheel.
Reply to
Jim Thompson

I believe it was a software that you could also throw scanned in plots.

--
Regards, Joerg

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Reply to
Joerg

Aha! I did recently buy "GetData Graph Digitizer" which can create numerical data points from graphs in data sheets.

Handy for creating subcircuits when all you have is a data sheet.

PSpice can do about any x-y plot you'd like, but I don't know how you'd do polar except with some innovative macros :-) ...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     |

                   Spice is like a sports car... 
     Performance only as good as the person behind the wheel.
Reply to
Jim Thompson

Reverse engineering ... ?

I think LTSpice can output polar data but I have never done it. I believe the command is "meascplxfmt polar".

--
Regards, Joerg

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Reply to
Joerg

Naaaah! Just making Spice models... mostly behavioral. For hire :-)

Recently did an IBIS gig... what a royal PITA :-(

But I did "copy" a National hard-drive controller chip once.

I was hired because I was totally ignorant of hard-driver controllers, was given only the public data sheet and nothing else.

Had to document every bit of reasoning my way thru the circuit design.

Ended up with chip design bearing absolutely no circuit resemblance to National's chip.

Outperformed it with a smaller chip size ;-)

For SSI (Grass Valley) before they got bought out.

I think there is a Smith Chart software around. ...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     |

                   Spice is like a sports car... 
     Performance only as good as the person behind the wheel.
Reply to
Jim Thompson

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