Differerntial demodulation using single-stage opamp and LPF.

Status
Not open for further replies.

Alex_bam

New Member
Hello,
I am designing a differential isolator via a capacitive coupling technique in which a control signal is differentially modulated and coupled capacitively to the differential demodulator side.
I have designed a demodulator using single-stage Opamp and LPF [Schematics attached]. The problem is the LPF's output signal swings between 2.8V to 5 V. How can I make LPF's output signal swing between 0-5V?
By doing so will make the Schmitt trigger's job easy to retrieve the output signal.

Thanks.
 

Attachments

  • 1.JPG
    206 KB · Views: 301
  • 2.JPG
    349.7 KB · Views: 293
With that circuit, I think the only way would be by using a negative supply rather than 0V for the "opamp" negative.
The source of the output devices is at 1.23V so it can never possibly pull lower than that, even if the output device was switched hard.

"Rail to rail" output opamps have a rather different topology than simple / dual supply types, eg. such as these examples:



 
I would use a voltage comparator. Set the reference at about 3.5 to 4 Volts. Add ~ 100 millivolts of hysteresis. Use a pullup resistor tied to 5 Volts on the comparator output.
 
Status
Not open for further replies.

Similar threads

  • Question
Single or Dual output on generator ?
Replies
3
Views
2K
KatharynBrowne
K
C
  • Question
Hooking up Amp meter to Baldor 220v single phase motor
Replies
13
Views
961
clockworkman
C
N
  • Question
How to check the stability analysis of complex opamp circuit in Ltspice
Replies
2
Views
849
Roff
C
  • Question
An opamp question I can't make sense of
2
Replies
22
Views
5K
MrAl
M
C
  • Question
A small problem question about opamps
Replies
5
Views
2K
Tony Stewart
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…