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will this fsk cicuit work?

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vikas1988

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hi guys. i found this fsk circuit in some old notes. is the design of this circuit correct? can a transistor be used as a switch as in this circuit?
 

You have been drawing a simulation circuit. Why don't you finish the simulation before asking others about the expectable result? Is it quiz?

A bipolar transistor can be used as an analog switch, but in the shown circuit, the input amplitude would be limited to 0.5 or 1 Vpeak.
Try to find out why by observing the waveforms at the invidual circuit nodes and thinking about basic BJT properties.
 

i did run the simulation and it worked. i want to know is it possible to connect a sinusoidal volatge source to the emitter without giving any dc bias.

and its not a homework problem
 

All this schematic does is use one or the other transistor as a clamp across the signal. It is incapable of reducing the unwanted signal to less then VCEsat of the transistor which is conducting. If you try to inject a signal at the emitter by lifting them from ground, all you achieve is a failure to clamp the unwanted input.

You would do better to use a simple analog switch.

Brian.
 

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    vikas1988

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i did run the simulation and it worked
Click to expand...
The collector voltage is clamped at about 1.4V, when an inverse collector voltage is applied. But the transistors can fairly work as a ground referenced switch (with reduced magnitude). It doesn't work reasonable as floating switch.
 

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    vikas1988

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