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Voltage level translation

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dspcode

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voltage translator 20mhz

I want to take the output of a 3.3v cpld and have it drive target
devices that may have various voltage standards -
(1/1.8/2.5/3.3/5 volts). The target voltage is available
as an input to the circuit. The circuit needs to operate at
20 MHz. I am trying to find a Simple circuit (e.g., 1 transistor
+ resistors) that will do this.

I've heard a common-base transistor configuration, with some
modifications will accomplish this. Also the delay should
be no more than 10 ns throught the translator.

All help is greatly appreciated.
 

dainis

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Look Maxim Logic Level Translators:
h**p://para.maxim-ic.com/compare.asp?Fam=bidirtranslators&Tree=Interface&HP=Interface.cfm
 

electronlover

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1 tran+1res

Ok, I just tried it out, and it works fine at 20Mhz (given my transistor, hehe sbc35)

You can just use one transistor and one resistor (like you said). I don't know what you mean by common base configuration, but using a common source is what I did.

(1v->5v supply)|
|
R
|---------translated output(1v->5v)
3.3v output-----N
|
|
GND


ok, so the R was a resistor of value 5k (probably totally different for you since our transistors will vary). The N was an NFET, and thats it.

things to worry about... on board capacitance. I used 10pf to work this one, and it will make it to within 100 millivolts of the peak magnitude at 20Mhz. You might think that you can just reduce the size of the resistor to get closer at the top...which you can, but then the bottom voltage starts rising also. Best thing to do is strike a happy medium and follow with an inverter on the new supply. Then everyone is happy. If you keep the capacitance on board down below 10pf this should work fine. Hope this helps!
 

coppervaporlaser

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i succesfully use the 74LTX541 level shifter which have 5Vtorerant in/outputs
 

Sobakava

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74LVX4245

a level translation IC....

74lvx4245 octal ....
 

rommelm

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Ok, I just tried it out, and it works fine at 20Mhz (given my transistor, hehe sbc35)

You can just use one transistor and one resistor (like you said). I don't know what you mean by common base configuration, but using a common source is what I did.

(1v->5v supply)|
|
R
|---------translated output(1v->5v)
3.3v output-----N
|
|
GND


ok, so the R was a resistor of value 5k (probably totally different for you since our transistors will vary). The N was an NFET, and thats it.

things to worry about... on board capacitance. I used 10pf to work this one, and it will make it to within 100 millivolts of the peak magnitude at 20Mhz. You might think that you can just reduce the size of the resistor to get closer at the top...which you can, but then the bottom voltage starts rising also. Best thing to do is strike a happy medium and follow with an inverter on the new supply. Then everyone is happy. If you keep the capacitance on board down below 10pf this should work fine. Hope this helps!
Yes... The charging path would be dictated by the resistor value... charging your load capacitor. The rise time will suffer. But for the fall time, it would be quick because of the transistor, your resulting signal would not be symetrical on the rise time and fall time.

Normally we use driver IC for this...
 

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