Transmitter output

power

IcMax

transmitter,

be

required

specfied

Thanks for the quick reply. So this means, if I use a NPN transistor (Q1) with emitter grounded and collector is fed through a resistor (R1) from Vsup, and if I connect the antenna aslo to the collector, then max collector swing and max possible current that R1 and Q1 can handle, will dictate the max RF power ?

Then what about the power that is dessipated by R1 and Q1 ?

Please reply. Harshana

the other reason is to reduce spurious

if you connect the antenna directly to the collector, any harmonics at

You should consider an LC tank circuit and low pass filter

Mark

"Maximum RF output" means maximum power.

Power = Voltage * Current (as you know)

You could increase the voltage, or the current, or both. The DC power supply places an upper limit on voltage swing. The transistor's IcMax rating places an upper limit on current; but, when designing a transmitter, you would typically allow the peak-to-peak collector voltage swing to be almost twice rail - the collector current is then dictated by the required output power. This assumes you have selected a transistor which is specfied as being capable of delivering that power.

Well - normally, collector resistors are only used in low-power, low-frequency (e.g. audio) amplifiers. That said, you could make an RF amplifier this way, but, as you say, power will be wasted in the resistor. That's one reason why LC matching networks are used.

Power dissipation in the transistor is unavoidable; however, efficiencies of (typ) 75% can be achieved for RF Class C amplifiers.