Hello, can somebody check my transistor amplifier schematic?

[michael1978]

Hi, can somebody tell me how to connect some component in this picture, i draw it but is not working because i have no bfg520 transistor, look this picture maybe i make mistake

 

[jedishrfu]

Can you provide some context here? What is the circuit for?

What did you replace the BFG520 transistor with? It seems you need to find an equivalent transistor or one that's similar and adjust the other compoenets as well.

I'm not skilled in electronics per se and can't comment beyond this. However, I figured other PF members would need to know what I'm asking here.

It seems thay are still selling this transistor:

https://www.nxp.com/products/rf/rf-...nsistors/npn-9-ghz-wideband-transistor:BFG520

 

[michael1978]

Can you provide some context here? What is the circuit for?

What did you replace the BFG520 transistor with? It seems you need to find an equivalent transistor or one that's similar and adjust the other compoenets as well.

I'm not skilled in electronics per se and can't comment beyond this. However, I figured other PF members would need to know what I'm asking here.

It seems thay are still selling this transistor:

https://www.nxp.com/products/rf/rf-...nsistors/npn-9-ghz-wideband-transistor:BFG520

one question, can you compare with mine circuits is everything ok, except transistor?

 

[berkeman]

Both schematics look basically okay to me. Is L1 supposed to be coupling to an antenna as the signal input?

When you say the circuit "is not working", what do you mean? Can you plot the DC solution? Are you trying to run a transient analysis? If so, what is your input signal?

 

[michael1978]

Both schematics look basically okay to me. Is L1 supposed to be coupling to an antenna as the signal input?

When you say the circuit "is not working", what do you mean? Can you plot the DC solution? Are you trying to run a transient analysis? If so, what is your input signal?

, I forgot to add signal, but if i put 1 v output is 313mV is okej?

 

[berkeman]

but if i put 1 v output is 313mV is okej?

No, this is an AC amplifier, with an assumed input source somewhere around L1.

 

[berkeman]

The 2V DC bias source is for setting the capacitance of that varacter diode, to make the input LC tank circuit resonate at the frequency of interest... It is not a signal input source.

 

[michael1978]

The 2V DC bias source is for setting the capacitance of that varacter diode, to make the input LC tank circuit resonate at the frequency of interest... It is not a signal input source.

Sorry one more question, is not working so good varactor because, in document the say min 0.8v and max 6V to change resonance, i don't undrestand, so input frequency must be 100MHZ right?

 

[berkeman]

is not working so good varactor because, in document the say min 0.8v and max 6V to change resonance

And the 2V bias is right in the middle of that range, right? You will fine-tune that input DC voltage to get the right LC resonance...

so input frequency must be 100MHZ right?

That's about what the output filter is tuned for, so yes.

 

[michael1978]

Sorry one more question, is not working so good varactor because, in document the say min 0.8v and max 6V to change resonance, i don't undrestand, so input frequency must be 100MHZ right?

input si

And the 2V bias is right in the middle of that range, right? You will fine-tune that input DC voltage to get the right LC resonance...

That's about what the output filter is tuned for, so yes.

Please sorry, for what we use te varactor? to tune from 88mhz to 108mhz right of not? why i can't change the frequency, can you explain more clear please, what input dc voltage you mean for varactor diode to change capacitance to tune to another station, because i read varactor with dc input increase and decrase the capacitance of varactor, and i put to 2v , do i need to put potentiometer to connect with varactor, of, how suppose to be working like this?, to change frequence

 

[berkeman]

This is a similar

Please sorry, for what we use the varactor? to tune from 88mhz to 108mhz right of not?

Yes, the reverse bias voltage of any diode changes its capacitance (because it changes the width of the depletion layer). The higher the reverse bias voltage, the wider the depletion layer and hence the lower the capacitance of the diode.

https://en.wikipedia.org/wiki/Varicap

You could use a hand-turned variable capacitor for that input tuning stage, or you can use a voltage-controlled varactor diode to change the input capacitance to fine-tune the input resonant frequency.

So L1 is part of the antenna input circuit, right?

 

[michael1978]

This is a similar

Yes, the reverse bias voltage of any diode changes its capacitance (because it changes the width of the depletion layer). The higher the reverse bias voltage, the wider the depletion layer and hence the lower the capacitance of the diode.

https://en.wikipedia.org/wiki/Varicap

You could use a hand-turned variable capacitor for that input tuning stage, or you can use a voltage-controlled varactor diode to change the input capacitance to fine-tune the input resonant frequency.

So L1 is part of the antenna input circuit, right?

But i use already varacator(voltage-controlled varactor), what i have to do more, because i want to use varactor, there is not more in use so much variable capacitor, what i need to change to work varactor can you help me,the L1 is part of oscillator, and i put signal between L1 and Right leads of capacitor C3

 

[berkeman]

But i use already varacator(voltage-controlled varactor), what i have to do more, because i want to use varactor, there is not more in use so much variable capacitor, what i need to change to work varactor can you help me

Sorry, I'm not able to understand what you said. It sounds like you have used varactor diodes before, and now you need to use one in this circuit. It is shown correctly in the circuit, as far as I can tell.

L1 is part of oscillator, and i put signal between L1 and Right leads of capacitor C3

If L1 is the secondary of a tuned antenna transformer, then coupling the input signal into the circuit single-ended with a connection between L1 and C3 does not work the same way. It's better to use a transformer for L1 to couple the input signal in differentially across L1.

 

[michael1978]

Sorry, I'm not able to understand what you said. It sounds like you have used varactor diodes before, and now you need to use one in this circuit. It is shown correctly in the circuit, as far as I can tell.

If L1 is the secondary of a tuned antenna transformer, then coupling the input signal into the circuit single-ended with a connection between L1 and C3 does not work the same way. It's better to use a transformer for L1 to couple the input signal in differentially across L1.

L1 is part of oscillator? i don't know rely, if i know i will tell you, me i just take from that picture, which i post it, i think is part of oscillator

 

[michael1978]

why in document this circuits works, what i make mistake

 

[berkeman]

Can you post a copy of your simulation schematic with the DC bias points labeled? Which version of SPICE are you using to simulate your circuit?

 

[berkeman]

L1 is part of oscillator? i don't know rely, if i know i will tell you, me i just take from that picture, which i post it, i think is part of oscillator

Is the circuit meant to be part of a radio receiver or a radio transmitter? Can you show us where you got the circuit from?

 

[michael1978]

Can you post a copy of your simulation schematic with the DC bias points labeled? Which version of SPICE are you using to simulate your circuit?

Is party of local oscillator in fm supere heter receiver, he do simulation ind ads2011

 

[berkeman]

Is party of local oscillator in fm supere heter receiver, he do simulation ind ads2011

Please provide a link to where you got it. Thanks.

 

[michael1978]

Is the circuit meant to be part of a radio receiver or a radio transmitter? Can you show us where you got the circuit from?

from here
https://www.eit.lth.se/fileadmin/eit/courses/eti041/VT2012/04a.pdf

 

[michael1978]

Please provide a link to where you got it. Thanks.

from here
https://www.eit.lth.se/fileadmin/eit/courses/eti041/VT2012/04a.pdf

 

[berkeman]

from here
https://www.eit.lth.se/fileadmin/eit/courses/eti041/VT2012/04a.pdf

Ah, it's a Clapp oscillator, not a receiver amplifier. Got it. I haven't used SPICE to simulate oscillators in the past, but I'm guessing you need to find the DC bias points with the oscillator part disabled, and then let it run starting at that DC bias point. It might take an initial (small) impulse input to start the oscillation going, though.

I'll google some for SPICE simulations of transistor oscillators to see if there are other tips suggested...

 

[michael1978]

Ah, it's a Clapp oscillator, not a receiver amplifier. Got it. I haven't used SPICE to simulate oscillators in the past, but I'm guessing you need to find the DC bias points with the oscillator part disabled, and then let it run starting at that DC bias point. It might take an initial (small) impulse input to start the oscillation going, though.

I'll google some for SPICE simulations of transistor oscillators to see if there are other tips suggested...

But i build in multisim, but is no problem i will build also in LTSPICE

 

[michael1978]

Ah, it's a Clapp oscillator, not a receiver amplifier. Got it. I haven't used SPICE to simulate oscillators in the past, but I'm guessing you need to find the DC bias points with the oscillator part disabled, and then let it run starting at that DC bias point. It might take an initial (small) impulse input to start the oscillation going, though.

I'll google some for SPICE simulations of transistor oscillators to see if there are other tips suggested...

Hello i start to build in LTSPICE so first i put varactor, but there is no bby40, i have only that in multisim
what do you think why is not working in multisim

 

[berkeman]

I'll google some for SPICE simulations of transistor oscillators to see if there are other tips suggested...

The search comes up with lots of useful ideas. Here's the google hit list:

https://www.google.com/search?q=spi...illators&ie=utf-8&oe=utf-8&client=firefox-b-1

And this PDF has a nice idea for the forcing function to use to "kick start" the oscillator:

https://m.eet.com/media/1148991/22768-52799di.pdf (see page 110 in the PDF version)

They use a damped oscillator input signal to kick start the oscillator and then let the oscillator circuit continue on its own after the exciting waveform dies out. Nice idea...

 

[michael1978]

The search comes up with lots of useful ideas. Here's the google hit list:

https://www.google.com/search?q=spi...illators&ie=utf-8&oe=utf-8&client=firefox-b-1

And this PDF has a nice idea for the forcing function to use to "kick start" the oscillator:

https://m.eet.com/media/1148991/22768-52799di.pdf (see page 110 in the PDF version)

They use a damped oscillator input signal to kick start the oscillator and then let the oscillator circuit continue on its own after the exciting waveform dies out. Nice idea...

View attachment 228449

Thank you very much for time and helping

 

[michael1978]

Thank you very much for time and helping

have a nice wekend,
in multisim you don't know ok, because i start to build, i did not find the type of varactor but leave i make you tired, thank a lootttttttttttttttttttt,
maybe somebody else know more about multisim
greetings

 

[michael1978]

Hello is anybody here who know to work with multsim, for my circuits thanks TO BEKERMANS he help a lotttttt,
but like i say to him i build in multsim circuit, and i try to build in ltspice but he does not have the type of varactor and transistor

 

[berkeman]

i build in multsim circuit

Can you post your Multisim circuit with the DC operating points labeled? If the simulator can analyze circuits, it can show the DC operating points that it calculates at the start of a simulation...

i start to build in LTSPICE

Good. Simulating circuits is much more commonly done in some variety of SPICE. It looks like Multisim is targeted at simulating larger systems (including circuits -- I wonder if they use some standard Berkeley SPICE engine to do that part of their simulations)...

 

[michael1978]

Can you post your Multisim circuit with the DC operating points labeled? If the simulator can analyze circuits, it can show the DC operating points that it calculates at the start of a simulation...

Good. Simulating circuits is much more commonly done in some variety of SPICE. It looks like Multisim is targeted at simulating larger systems (including circuits -- I wonder if they use some standard Berkeley SPICE engine to do that part of their simulations)...

Can i do it tomorow, i am tired its 1clock night, sorry goodnight have a nice day or sleep

 

[michael1978]

Can you post your Multisim circuit with the DC operating points labeled? If the simulator can analyze circuits, it can show the DC operating points that it calculates at the start of a simulation...

Good. Simulating circuits is much more commonly done in some variety of SPICE. It looks like Multisim is targeted at simulating larger systems (including circuits -- I wonder if they use some standard Berkeley SPICE engine to do that part of their simulations)...

Goodmorning, i do it, everytime he simulated, now is not working

 

[michael1978]

Can you post your Multisim circuit with the DC operating points labeled? If the simulator can analyze circuits, it can show the DC operating points that it calculates at the start of a simulation...

Good. Simulating circuits is much more commonly done in some variety of SPICE. It looks like Multisim is targeted at simulating larger systems (including circuits -- I wonder if they use some standard Berkeley SPICE engine to do that part of their simulations)...

Sorry i fall again in sleep, what is Berkeley SPICE, do you know any good spice software which are able to do this? so maybe i can download, i make dc point agan but is blocked now

 

[michael1978]

Can you post your Multisim circuit with the DC operating points labeled? If the simulator can analyze circuits, it can show the DC operating points that it calculates at the start of a simulation...

Good. Simulating circuits is much more commonly done in some variety of SPICE. It looks like Multisim is targeted at simulating larger systems (including circuits -- I wonder if they use some standard Berkeley SPICE engine to do that part of their simulations)...

here is dc points current and voltages

 

[NascentOxygen]

It seems incongruous to have a 220uF cap in the middle of a HF oscillator (C1).

 

[Baluncore]

It seems incongruous to have a 220uF cap in the middle of a HF oscillator (C1).

C2 = 220uF is clearly a mistake. 220pF maybe, but an electrolytic would have a higher inductance than the tuning inductor.
I began to model the circuit with LTspice but have not made it oscillate yet.

 

[michael1978]

C2 = 220uF is clearly a mistake. 220pF maybe, but an electrolytic would have a higher inductance than the tuning inductor.
I began to model the circuit with LTspice but have not made it oscillate yet.

Hello, realy, why in ads 2012 he worked, i also download simetrix simulation i built and i get error dcop(error)
i am try to download ads 2012 and to build and to see….

 

[michael1978]

C2 = 220uF is clearly a mistake. 220pF maybe, but an electrolytic would have a higher inductance than the tuning inductor.
I began to model the circuit with LTspice but have not made it oscillate yet.

It seems incongruous to have a 220uF cap in the middle of a HF oscillator (C1).

I rey also 220p but is not working

 

[michael1978]

I did not do it in ltspice because i start with varicap, and i did not find the model and i stop

 

[Baluncore]

You do not need a varicap to check this circuit. Just use a fixed capacitor, then you can step that parameter value.

Some oscillators won't, because of the numerical stability and the perfection of the SPICE model, so it takes a kick to get them going. Sometimes a big kick will give some idea of where the losses are and why it is so dead.

At other times only the smallest tickle is needed which is the case with this Clapp oscillator SPICE model. One solution is to set a starting current of say 1 uA in the first tuned circuit by using an initial conditions statement, for example;
.IC I(L1)=1u0

 

[Baluncore]

This circuit may start without a tickle, it depends on your partricular simulation parameters. Frequency is about 100 MHz.

The pattern is a beat between the pixel pitch and the 100 MHz sinewave.

Two LTspice files attached, remove the .txt extension to run.

 

[michael1978]

This circuit may start without a tickle, it depends on your partricular simulation parameters. Frequency is about 100 MHz.

View attachment 228585

View attachment 228586
The pattern is a beat between the pixel pitch and the 100 MHz sinewave.

Two LTspice files attached, remove the .txt extension to run.

Thank you lottttt sirr

 

[michael1978]

This circuit may start without a tickle, it depends on your partricular simulation parameters. Frequency is about 100 MHz.

View attachment 228585

View attachment 228586
The pattern is a beat between the pixel pitch and the 100 MHz sinewave.

Two LTspice files attached, remove the .txt extension to run.

Hello sir, how you did please, how you find the corrected transistor and varicap, i am jeloze than i don't know,

 

[Baluncore]

how you did please, how you find the corrected transistor and varicap,

I did NOT find the right components, I just made it work well enough to test. I could make the components if I needed them.
I selected the transistors because they will work in that application at 100MHz, they are not optimum.
I did not try to model the varicap as it is not needed to test the design.There are only two varactors in the Ltspice standard library. It is there on the diagram as a "place-holder".

There are many sources of extra models for LTspice. You can edit components from other versions of spice.
You could join the Ltspice group. https://groups.yahoo.com/neo/groups/LTspice/files
then watch https://groups.yahoo.com/neo/groups/LTspice/conversations/messages

See also; http://ltwiki.org/?title=Main_Page
http://www.analog.com/en/design-center/design-tools-and-calculators.html

 

[michael1978]

I did NOT find the right components, I just made it work well enough to test. I could make the components if I needed them.
I selected the transistors because they will work in that application at 100MHz, they are not optimum.
I did not try to model the varicap as it is not needed to test the design.There are only two varactors in the Ltspice standard library. It is there on the diagram as a "place-holder".

There are many sources of extra models for LTspice. You can edit components from other versions of spice.
You could join the Ltspice group. https://groups.yahoo.com/neo/groups/LTspice/files
then watch https://groups.yahoo.com/neo/groups/LTspice/conversations/messages

See also; http://ltwiki.org/?title=Main_Page
http://www.analog.com/en/design-center/design-tools-and-calculators.html

Ohh Man is difficult for me, i don't have experience, but i working cool a,
may i ask you someing did you here about simetrix spic i did the same like you did
and i get strange waveform

 

[tech99]

This looks like spurious oscillation at a much higher frequency. This is why RF engineers are special people.

 

[michael1978]

This looks like spurious oscillation at a much higher frequency. This is why RF engineers are special people.

You want to say is correct waveform?

 

[Baluncore]

may i ask you someing did you here about simetrix spic i did the same like you did and i get strange waveform

It looks to me like the circuit simulation is switching and ringing. Maybe SIMetrix is trying to make it switch like the switching-power circuit SIMetrix is designed to simulate. Apparently SIMetrix runs much faster than Spice, which might explain why it gets it so wrong.

I have not used SIMetrix, nor do I know the circuit or simulation parameters that you have used.

 

[michael1978]

It looks to me like the circuit simulation is switching and ringing. Maybe SIMetrix is trying to make it switch like the switching-power circuit SIMetrix is designed to simulate. Apparently SIMetrix runs much faster than Spice, which might explain why it gets it so wrong.

I have not used SIMetrix, nor do I know the circuit or simulation parameters that you have used.

Hello sir, i find good software, and i have gratis version 7.2 intro,, if you want i can send you...
sorry i make you tired, i make the same like your circuits i just change the transistor bfg520/PS
I configure SEE THE PICTURE

I change the resistor to bf199 and i get this(the same configuration)

 

[Baluncore]

It is hard to read your diagrams, but your C10 looks like 6.8pF. Increase that to 47pF, connected to ground. Open circuit the V3 source and run the simulation for 100usec. If it does not then start and run, you must experiment with a V3 pulse of 100mV or an initial current of maybe 100uA in L1=100nF.

Find the initial current or pulse needed to make it ring then die. That tells you the phase and gain are insufficient to sustain oscillation. Find out how sensitive it is to small changes in component values. Adjust one component at the time to make it ring at about the right frequency for a longer time. When you have sustained oscillation, reduce or remove the initial current used to initiate the oscillation during testing.

 

[michael1978]

It is hard to read your diagrams, but your C10 looks like 6.8pF. Increase that to 47pF, connected to ground. Open circuit the V3 source and run the simulation for 100usec. If it does not then start and run, you must experiment with a V3 pulse of 100mV or an initial current of maybe 100uA in L1=100nF.

Find the initial current or pulse needed to make it ring then die. That tells you the phase and gain are insufficient to sustain oscillation. Find out how sensitive it is to small changes in component values. Adjust one component at the time to make it ring at about the right frequency for a longer time. When you have sustained oscillation, reduce or remove the initial current used to initiate the oscillation during testing.

do you have simetrix, i can gi

It is hard to read your diagrams, but your C10 looks like 6.8pF. Increase that to 47pF, connected to ground. Open circuit the V3 source and run the simulation for 100usec. If it does not then start and run, you must experiment with a V3 pulse of 100mV or an initial current of maybe 100uA in L1=100nF.

Find the initial current or pulse needed to make it ring then die. That tells you the phase and gain are insufficient to sustain oscillation. Find out how sensitive it is to small changes in component values. Adjust one component at the time to make it ring at about the right frequency for a longer time. When you have sustained oscillation, reduce or remove the initial current used to initiate the oscillation during testing.

To which circuit with bc199 or bfg250?because i have 2 one with bc199 and the other with bfg250? i change c10 to 47p is more better waveform, do you have any software i can send you my file, and to run not 5u but 100usec, and to change only the voltage of v3 righ?