Electronics > Projects, Designs, and Technical Stuff

AC coupled Differential op amp bias gain -100 Vcc/2 resistor dependencies?

(1/1)

beduino:
Hello,
I'm a little bit confused why in this quite good intro  (AC_coupleddifferential_amplifier_Vbias_Vcc2-marked) to AC coupled differential op amp, there is some kind of dependency between R2 and R3/R4 voltage divider for Vbias?
I've R1=1k and looking for gain x100 to saturate opamp to have pin change interrupt on MPU input pin, so I do not need measure amplified voltage difference, but just generate interrupt - in owrst case scenario no problem if I will not be able distinguish between pin change from 0/1 nor 1/0.
I'd like to connect to this differential op amp a few loops of wire to detect magnet crossing nearby inducing voltage peaks - it will be clamped by to anti-parallel shotky diodes to limit input voltage difference to less than 0.7V probbaly depending on how many loops of wire, its crosssection area, distance and speed of magnet etc...

Any idea howto properly choose value for R3=R4, while it looks like R2 should be 100k and by rearanging this formula for R2=R*R/(R+R)=0.5*R -> R3=R4=R=2*R2 

R3=R4= 200k ?

I've already designed PCB with op amp in differential amplifier configuration like shown here, but before testing real circuit,
I'd like to ensure those resitor values makes sense?  :-BROKE

I watched great Dave opam tutorial and also spotted similar differential aamplifier circuit, but probably without bias, or maybe a I missed something?
I'm interested in AC signal difference multipled by gain at bias voltage Vcc/2, so I assume R3=R4 in split resitor example linked below.

Regards.

Navigation

[0] Message Index

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod