[time-nuts] Squaring Tbolt 10Mhz output

Charles P. Steinmetz charles_steinmetz at lavabit.com
Thu Mar 24 06:42:05 UTC 2011


>One problem that is evident when a simple longtailed pair 
>(differential amplifier) is used to convert a sine wave to a square 
>wave is the tilt that is evident in the waveform when the output 
>transistor is conducting. This is due to feedthrough from the input 
>signal via the emitter base capacitance of the input transistor to 
>the emitter of the output transistor.
>The attached circuit schematic illustrates one classical method of 
>minimising this tilt.
>Compensation isn't perfect due to the voltage dependence of the 
>emitter base capacitance but the tilt can be significantly reduced,

I have used the attached circuit, which is a bit simpler, to the same 
end.  For the reason you stated, the compensation is not perfect, but 
it is surprisingly good.  The compensation slows the rise and fall 
times by about 1 nS, from about 7.5 nS to about 8.5 nS.

This circuit produces 5 Vpp output -- for 3.3 Vpp output, using a 121 
ohm tail resistor should work.

Best regards,

Charles



    
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