[time-nuts] Need tiny 5MHz 10x amplifier

Charles Steinmetz csteinmetz at yandex.com
Sat Nov 28 22:55:37 EST 2015

Poul-Henning wrote:

>I need to convert a 5MHz 0.2Vpp AC coupled sine signal to a 3.3V
>CMOS compatible logic signal.
>The "default" comparator based circuit either requires a negative
>supply or 4 resitors for biasing the input and setting the zero level.
>(The hysteresis resistor is the same in both cases).

The LT1720** works on a 3.3v single supply, and has internal 
hysteresis.  Just ground one input, ground the other through a 
resistor, and attach your AC-coupled signal (best if you can use 
equal resistors to ground on the two inputs, but if the signal 
termination is 50 ohms the other input can be 0 ohms to ground; even 
1k ohm would probably be OK).

Note that the LT1720 is specified for inputs to 100mV below V- 
(ground, in this case) and your 200mVpp signal pushes it right to the 
limit.  A bit of attenuation is probably a good idea.

**  The 1720 is a dual comparator, so you'd have an extra to use or 
ignore.  Alternatively, the 1719 is a single with extra features that 
you could ignore.  Either should work well in your application.

Best regards,


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