Amplification of Signal to TTL signal

[scdoro]

Hi,
I need a TTL input signal to my MCU, however my input signal from crystal has a very small amplitude of less than 0.7v . I need to amplified it to give me a TTL signal of ( 0V = logic 0 , more than 3 V = logic 1 ) .
May I know how can i go abt designing it ?? using ??
Thanks a lot of ur help

 

[IanP]

One of options will be to use a comparator/opamp as comparator and convert this 0.7V (or less) signal to CMOS/TTL.
Your initial signal can be connected to comparator's (+) input, and on comparator's (-) input you can adjust level with a potentiometer ..

 

[rfmw]

I would do it like the picture shows. You must optimize the resistors for optimal operating point, but in general, the circuit should work as it is... And increase the coupling capacitor value

hope this helps,
rfmw

 

[scdoro]

Hi,
if i use the transistor, will it affect the input frequency ? Cuz my application is to build a frequency counter to measure the frequency of cystal, and crystal has very small signal, what i am afriad is
1) will the frequency be affected ?
2) and will the signal from the crystal is too small to be detected cuz when connect up tp my frequency counter, the signal become zero.

thanks for ur help

 

[rfmw]

1. Yes, the frequency will definitly change because of the load. Thats called the "load pull" effect.

What you should do is to buffer the crystal oscillator output with a transistor amp or something like that...

 

[renato]

What is the frequency of your crystal ? If you are these crystal to RTC of your uC (32768Hz or same magnitude) don't worry about changes do transistor. Temperature could afect you clock more than others factors.

Anyway, I sugest you use an operational amp or a diferential working as comparator. THe first one is easy to work, but averything depends on frequency you are working. If after level translation you need a square wave, use a logical gate to do it.

Best regards,

Renato

 

[scdoro]

Hi,
i have built the transistor cct as mention above but it doesn't seem to work at all..
May i know what the 4.7K resistor for ??
After pumping in the signal , i can't detect any signal from the capacitor..
thanks a lot

 

[suromenggolo]

if yo use crystal oscilator with TTL output, use another schematic of crystal oscilator, like TTL component to bulid crystal oscilator. with 7404 (inverter TTL)

please send your crystal oscilator schematic.!