Designing an amplipier

[zachi]

amplipier

Hello,

OK, I know how to analyze an amplifier circuit with transistors. but how do I design an amplifier ??? how do i decide which type of transistor to use ??? what is the value of each resistor, capasitor & coil....???

are there any ground rules ?? or is trying until hitting the correct combenation ???

thanks in advance,

 

[Edward_2288]

amplipiers

hi...

it all depends on your specs. starting from your spec, then u can choose which topology is suitable.

 

[zachi]

Let say with the following spec : (from imagination...)

Av = 50
Ai = 30
freq = 30-100MHz
Z Load = 32ohm
Vin= 1mV


do I need to know anything more ? when you say topology - do you meen CC\CE\CB ???

 

[radiohead]

Hi,

In desiging amplifiers, you have to have experience to make the right selections. In your case, I would make the following remarks:

1.With this bandwidth, if you really want a flat response, you need feedback! You can try by selecting a really fast opamp. Or RF transistors will do well also. But you will have to take care not to use too many stages before applying feedback, because instabilities could occur! Another option is to use mismatch to flatten the gain of the amplifier. So the operating frequency defines the transistor or amplifier to use!

2.The output load defines the bias current of the last stage. When applying feedback you can use a power amplifier for the last stage (like in opamps). If not you need a class A stage to minimize output distortion. The maximum output voltage swing is the output current swing times the load resistor!

3.The stages before the output stage can have smaller bias current because the signal is smaller there (linearity).

4.You need 50 voltage gain, or 34dB, you need at least two stage to realize this. If you use feedback, perhaps three stages are necessary. But beware of oscillations! Often it's better to use two cascaded stages with feedback of their own then!

5.It's not common to define Ai in discrete amplifyers (different from current amplifiers in IC design!). Most of the time, we only specify voltage gain or power gain. Ai puts a restriction on the input impedance of the amplifier, as it should be Zout*Ai/Av, or about 50Ohm.

These are specific remarks for this case. The selection of the optimum topology depends on other things, like best gain, linearity, noise performance, .... Read some literature to find out about these!

 

[guamak_menanak]

It's hard to teach you in this forum by just telling you what to do and don't! The better way to get the knowledge is by trying to design it by your self! There are a lot of website/paper to teach you how to design a simple amp! A good book is a good alternative to gain your knowledge in the design field because we need some equation to do make the design calculation such as the gain,f3db,stabilty,noise etc..

Don't worry to fail, because more you failed...you will gain more knowledge!

My suggestion is try to design a simple amp, such as a single amp! do your simulation and try to do reverse engneering, try to get the result via your calculation!

Enjoy to fail, you will feel very happy when you are succeed:lol:

 

[zachi]

thanks !!!

can you recommand me a good (and easy to use) simulation software

 

[v_naren]

its very strange that you are able to analyse amplifiers but not design them. I really wonder how is it possible....I am pretty sure that the place where u learnt analysis also must have dealt with design??

anyways

How about trying to read Electronic circuits: Discrete and Integrated by Schilling and belove and Co.

its the best book for learning to design simple single stage CE,CB,CC and mos counterparts.

all the best of luck

 

[guamak_menanak]

There are a lot of software to do the design and analysis!

You can try P-SPICE as a simple and easy one! It's a Windows base software! You can download the software on the P-SPICE website! I think you can buy it at soft store!

 

[mehulpachchigar]

hi
friend
i need ur help to construct the power amplifier for the range of 10Mhz friequency.
if you have some circuit idea or related web sites than please send it my e mail.
thankz.

 

[mehulpachchigar]

Hello,

OK, I know how to analyze an amplifier circuit with transistors. but how do I design an amplifier ??? how do i decide which type of transistor to use ??? what is the value of each resistor, capasitor & coil....???

are there any ground rules ?? or is trying until hitting the correct combenation ???

thanks in advance,

 

[duncan94022]

I don't think you can get free student version of PSpice anymore, just an evaluation copy. Some older verisions of PSpice are archived at **broken link removed**

 

[radiohead]

Ever found out about APLAC? Very powerful simulator. Has everything, even harmonic balance. They used to provide a free student version (limited memory size). This one should do the trick!

 

[lord_of_destruction]

designing amplifiers depend mainly on some assumptions where for a Common emitter as an example
u can assume that current in universal divider = 10 and 11 * (base current)
and Volt on emitter resistance = 0.1 Vcc
and Vce = 0.5 Vcc
but these assumptions mainly depend on the number of unknowns u have in the circuit u design

 

[sunking]

you can refer to "CMOS Analog Circuit Design", allen & holberg.
it is a very good book

 

[artem]

Student versions could be found on hxxp://www.engr.pitt.edu/coe-courses/Labs/Software/Pspice/index.htm

ver 8 and 9.1 + plus extracted user guides in pdf acrobat formats .

 

[raymond_luo2003]

You can refer to a lot of book for amplifer design since that's is very basic and most important topic. It is quite difficult to say step by step online. What should you do is just read a book, understand your SPEC, get a whatever tool sunch as HSPICE to simulate it.

Raymond