can common emitter amplifier do with a 2v signal?

[ddt694]

when design a high frequency(10M - 100MHz) amplifier, if the input signal voltage is about 2v p-p, i use common emitter amplifier, can the amplifier work?

my mean is: because the emitter is tied to gnd, the voltage between base and emitter(gnd) is only 0.7v, most of the signal may be voltage limited, the amplifier cannot work rightly. say, all the common emitter amplifier can not do with a input signal whose voltage greater than 0.7v.

i know i am not right, but why?

 

[samcheetah]

you should have attatched a schematic of the circuit.

the collector current depends on the voltage between the base and the emitter. the more the voltage the more the collector current. a voltage of 0.7+ will bring the transistor into conduction. in a common emitter class A amplifier the transistor is already in conduction (active region). the input signal varies the voltage at the base and hence the collector current varies.

the result will be that a magnified replica of the base-emitter voltage will be produced at the collector.

the only thing to take care of is that the input voltage should not be high enough to drive the transistor into saturation which will result in clipping of signal (distortion)

i hope that helps

 

[dsjomo]

A 2Vpp signal means that the voltage amplitude is 1V, this gives rise to high collector current and base input current.

condition 1: you burn your transitor
condition 2: base input current heavily loads the signal source and distorted the signal because the signal source's limited driving ability.
condition 3: the signal is clampped. Just like what happened in condition 2, this is the extreme case of condition 2.
condition 4: you successfully amplify the signal. You made an PA.

 

[fletcher]

If you use it with base resistor the volatge on base-emitter is not 2 V.
Without base resistor I don't know your answer.

 

[ddt694]

what i confused is:

almost all textbooks divide the topic of amp design into LNA and power amp design,say, very low power amp design and high power amp design. but few of books deal with mid power amp design.

for example, a 2vpp/50ohm input signal amp or buffer amp design, i know this amp is neither LNA nor PA. what is the design rules on earth?

 

[g579]

Why not use a ballast resistor in the emitter ?

 

[btbass]

You need to put a resistor between emiter and ground. Choose R1 and R2 so that the collector sits at mid rail, choose the emitter resistor to set the desired bias current. The gain will now be R3 divided by the emiter resistor. To increase gain, bypass the emiter resistor with Capacitor.

 

[ddt694]

You need to put a resistor between emiter and ground. Choose R1 and R2 so that the collector sits at mid rail, choose the emitter resistor to set the desired bias current. The gain will now be R3 divided by the emiter resistor. To increase gain, bypass the emiter resistor with Capacitor.

hi, btbass
Thanks for your help. I know this method is often used in low frequency operation.
In microwave frequency, if this method has bad influence on circuits' stablization?

In addition, almost all RF power transistors' emitter are required to tied to ground, can they amplify a input signal with voltage larger than 0.7v?