The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> Analog Design >> How does this rectifier work?
https://designers-guide.org/forum/YaBB.pl?num=1393290522

Message started by Jacki on Feb 24^th, 2014, 5:08pm

Title: How does this rectifier work?
Post by Jacki on Feb 24^th, 2014, 5:08pm

Hi All,

I read this paper "A Highly-Linear Radio-Frequency Envelope Detector for MultiStandard Operation", and cannot understand how the rectifier works.
If we see the figure below, the positive current Iin+ and the negative current Iin- will summed to be zero at the drain of M5. It cannot sum the current directly. The simulation gives me the same result.
By the way, I try to realize an envelope detector by using this circuit (OTA before the rectifier is not shown here), but I cannot get the rectified envelope whatever I change the value for the RC network. Could anybody advise me the comments?
Thank you.
Jacki

Title: Re: How does this rectifier work?
Post by aaron_do on Feb 24^th, 2014, 9:21pm

Hi Jacki,

looks like M1 and M3 are diodes. When the signal goes high, the current Iin is burnt in M1, and when the signal goes low, the current is sent to the output. The differential operation makes it a full-wave rectifier, and the RC cleans it up.

If you want to know what's wrong with your simulation I suggest you post some results. Since this circuit only works on a large-signal principle, make sure Iin is large enough to turn ON/OFF the transistors M1/M3. I suggest you simulate the circuit with a PSS analysis and sweep the magnitude of Iin. To see the gain, plot the DC component of the output.

regards,
Aaron

Title: Re: How does this rectifier work?
Post by Jacki on Feb 25^th, 2014, 10:23am

Hello aaron_do,

Thank you very much. I also consider it could be the large signal simulation orelse it doesn't need rectifier. So I need a very good Gm to convert the input voltage signal to large current signal, also try to reduce the bias voltage for rectifier.

Title: Re: How does this rectifier work?
Post by aaron_do on Feb 25^th, 2014, 4:49pm

Hi Jacki,

Quote:

So I need a very good Gm to convert the input voltage signal to large current signal

I think you have it backwards. The circuit you attached takes a current as the input, so you need to make sure the current is large enough that it is converted into a large enough voltage to switch ON/OFF the transistors.

Aaron

Title: Re: How does this rectifier work?
Post by Jacki on Mar 1^st, 2014, 3:29pm

Hello Aaron,

Thank you very much for your comments. I have played this rectifier well now.