Layout problem - common centroid techniques

[Monady]

Layout problem

Hi dear all friends,
i want to draw layout of comparator used in my ADC. this comparator must be so accurate thus i have to use of common centroid techniques. preamplifier used in my work consists of differential difference amplifier followed by regenerative cell. unfortunately i couldn't find any hints about laying out differential difference amplifier in any books. I would be appreciate if any body give me some help about this issue(with reference please).

Thx in advance

P.s.:i found some things in some dissertations but unfortunately they didn't use of any references.

 

[erikl]

Re: Layout problem

I would appreciate if any body give me some help about this issue

You can find a good summary on layout symmetry issues in Behzad Razavi's book "Design of Analog CMOS Integrated Circuits", Chap. 18, Sec. 18.2.2 Symmetry .

In your JPG, the layout geometry (d) is better than (e) because of better D1-D2 symmetry. Take care that its routing is equally symmetric and so doesn't deteriorate the total symmetry.

 

[Monady]

Thx for reply. i read some books about layout such as: [Design of Analog CMOS Integrated Circuits(Razavi)], [CMOS Circuit Design, Layout, and Simulation(Baker)], ......
but none of them explained any things about differential difference amplifiers (just simple differential pair transistors is described). i just want a reference in order for report in my thesis. i used of layout depicted in pic (d) but i want a well known reference for this geometry.

 

[erikl]

... none of them explained any things about differential difference amplifiers

I think a differential difference amplifier is nothing else than an instrumentation amplifier, s. e.g. here, p.3. And in the IEEE series you can find quite a few papers about this structure.

 

[Monady]

dear erikl, i know all things about differential difference amplifiers! i just want some references about laying this circuit out. Thx for references but i couldn't find any things about layout in "A Differential Op-Amp Circuit Collection".

 

[erikl]

... couldn't find any things about layout in "A Differential Op-Amp Circuit Collection".

Of course not, dear Monady! How can you expect to find a special report on layout of a differential difference amplifier? What, do you think, would be so special for it? The one and only criterion on layout is the necessary symmetry accuracy of its accuracy-responsible structures, totally independent of the circuit function itself.