Amplyfier for 20Mhz signal

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It's a little hard to read, but I believe you have a collector resistor of 47kΩ which is much too high for the collector stray capacitance. For a representative stray capacitance at the collector (transistor plus connection wire/trace plus load) of 20pF the collector resistance can be no more than 400Ω to generate a 20MHz sine-wave. If you want to generate a digital square-wave, the resistance would need to be even lower or else go to a push-pull or totem pole amplifier stage.
 
You will have a lot of difficulty amplifying a 20MHz signal. Firslty you need to put a 4k7 on the base and another 4k7 to ground to get the transistor to turn off.
You may need to decrease the load resistor to 4k7 and then you may need to use a faster transistor.
 

is a sine wave so what type of transistor would you recommend? because I tryed with a HEX inverter and it works, but I want to use a transistor.
 
I have tryed with smaller resistant but it always stays high, and no resistant is from 1.8V to 2.5V sine wave
 
Something is definitely wrong with your circuit. But a transistor will certainly attenuate the signal at 20MHz and this may be the fault of the transistor.
You are lucky to get a chip to work at 20MHz.
 
colin55 said:
Something is definitely wrong with your circuit. But a transistor will certainly attenuate the signal at 20MHz and this may be the fault of the transistor.
You are lucky to get a chip to work at 20MHz.
Click to expand...

so do you think it can work with this transistor **broken link removed**
 
I have done exactly what you have done with 100MHz transistors and the signal was attenuated so much that the result was poor-to-useless.
Use the chip.
 
Icemetal said:
so do you think it can work with this transistor **broken link removed**
Click to expand...

look at the switching characteristics ... if you add up the times and invert you get 3MHz. just use the chip, at least you only have to worry about it's delay.
 
I just need to use a transistor because I have like 50 boards to fix and I can't just put a chip on top of each, thats why I was looking for a transistor solution
 
If you don't need voltage amplification then you might try using the transistor as an emitter-follower with about a 400Ω emitter resistor.
 
yeah the fet wont work, what I need is to increase the current not the voltage, so I can drive many chips because the 20MHZ signal is being drop by the other chips
 
crutschow said:
That won't affect the problem of driving the stray capacitance at that frequency.
Click to expand...

very true, but he gave no indication that i recall at the time of what he was driving. best he can do with a transistor band-aid is to put in a FET and drop the drain resistance to the dissipation limit of the FET
 
Icemetal said:
yeah the fet wont work, what I need is to increase the current not the voltage, so I can drive many chips because the 20MHZ signal is being drop by the other chips
Click to expand...
So try the emitter follower circuit I suggested. It has a voltage gain of near 1 and has current gain.
 
Ubergeek63 said:
very true, but he gave no indication that i recall at the time of what he was driving. best he can do with a transistor band-aid is to put in a FET and drop the drain resistance to the dissipation limit of the FET
Click to expand...
He doesn't need to mention his load. Even with a typical minimum circuit stray capacitance value, a common-emitter or common-source will not be able to drive it at 20MHz unless the collector/drain resistor is a low value.
 
so any other ideas how to get enough current for this circuit to work, i tried putting a 10K pot and try to find the resistant that way but it same problem the signal still weak
 
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