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

Attila Kinali attila at kinali.ch
Sat Nov 28 21:02:13 EST 2015


On Sun, 29 Nov 2015 00:35:31 +0000
Poul-Henning Kamp <phk at phk.freebsd.dk> 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).
> Since space is a bit tight, I've been trying to find something like
> a "x10 self-biasing amplifier" but without luck.

Ugh.. you are asking difficult stuff. 0.2Vpp is very little signal
to work with. There are two options that come to my mind at this late
hour. One would be to use an 74LVC14 with an series resistor at the
input and one resistor from output back to the input. Kind of like
an inverting ampilier. This because the hysteresis of the 74lvc14
is too large for the 0.2Vpp. But I admit this is a hack. For an
one off system doable, but I wouldn't recommend it for anything build
more than once.

An alternative are fixed gain amplifiers, which do not need any feedback
resistors and at times offer a pin with bias voltage. Ti has some of them[1].
I'm pretty sure others, like Maxim and Linear have them too.

			Attila Kinali

[1] http://www.ti.com/lsds/ti/amplifiers-linear/fixed-gain-products.page

Reading can seriously damage your ignorance.
		-- unknown

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