The correct BJT transistor selection

transistor selection chart

Hi,

I have a problem in transistor selection. I get a few BJT transistors from a PDK. But I do not know to choose which one is suitable for my design. What transistor characteristics should I analyze in order to get the suitable one?

Thanks

lucky8

transistor selection

Many, let's proceed:

1) Working frequency and associated gain requested; this determines the transition frequency; choose a transistor with at least four times the Ft calculated;

2) C-E Voltage

3) Dissipated power;

4) input and output impedance

5) Case

And many others

Mandi

high frequency transistor selection table

First you didn't mentionated the aplication: amplifier in small signal or great signal or conmutation, low frequency or high frequency.

Your request is very wide. There are so many aplications of transistors.

bjt selection

it is for a high frequency application

My personal selections chart:

Current density is the most important criteria!

There are 4 different magic points in the current density chart.

1. Current density where the IE*RE<Offset Voltages

Take a 0.35u x 1u emitter open device. Typical RE=120 Ohm. Offset Typical 1mV. Then the current density is 8.3uA. That is important for bandgap cells or similar application which where you possible could not compensate the RE

2. Current density where the noise impact from RB and IB get about equal. If you design a LNA you could reduce the NF by increasing the device size because RB would go lower. But at the same time Ft goes down and the base current induced noise goes up. So there is a optimum. This optimum is typical about a factor 3-10 below the peak Ft.

3. Current density where Ft is max. That is for current amplifications.

4. Current density where DC Beta goes low. That is typical some factor above the current density where Ft is max. You should use that where minimum collector capacitance for current sources is needed.

The application is for an amplifier or for the digital area?
low power or high power?