Hello everyone again

My problem simply is that I connect a zero gain buffer between two circuits (low-pass filter and subtractor)

But what Wonder me, that there is a voltage drop in the buffer stage of about 1.5 volt

Can anyone explain to me why this happened?

Is the solution to overcome this problem is to connect a buffer stage with gain?

Thank you in advance

 

Check the specs in the datasheet. Maximum input is V+ minus 1.5V. You're providing 5V as V+, so the maximum input is 3.5V.

 

Please check the output side as attached circuit, the output voltage as:
Vout = Vcc - (Vbe1_Q11+Vbe2_Q12) - Vce_Q11 - V_Ro (V_Ro is the voltage cross on the output resistor)
= 5V - (1.3~1.4V) - (0.1V~0.2V)- V_Ro


LM358 datasheet -- Please check the datasheet on page 12 and to see the output side.