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Design >> Analog Design >> Connecting analog power domains in the same chip in ICs (Integrated Circuits)
https://designers-guide.org/forum/YaBB.pl?num=1415029369

Message started by Tako on Nov 3^rd, 2014, 7:42am

Title: Connecting analog power domains in the same chip in ICs (Integrated Circuits)
Post by Tako on Nov 3^rd, 2014, 7:42am

I have a following issue, which I didn't see in IC books: I would like to know if it is possible to send analog signals (sin waves) between two power domains in an integrated circuit. The issue looks as at the picture.

I have never had a problem with sending digital signals between two different power domains as it is done through level shifters / level converters. However, I never thought about sending analog signals between two power domains. Is it done using protection diodes as at the picture?

Of course, signal send from 3.3 V domain is limited to 2.5 V. This sinusoidal 3.3 Vpp emphasizes that signal is send from 3.3 V domain to 2.5 V domain and that maximum signal that can appear on the line is 3.3 Vpp.

Title: Re: Connecting analog power domains in the same chip in ICs (Integrated Circuits)
Post by Tako on Nov 3^rd, 2014, 8:14am

Oh my goodness . . . I had an eclipse of the mind at the end of a work day . . . Of course I can connect two power domains using capacitor + voltage divider. See the picture.

Title: Re: Connecting analog power domains in the same chip in ICs (Integrated Circuits)
Post by loose-electron on Nov 3^rd, 2014, 5:03pm

common strategy -

1 convert signal to a differential current (think diff pair)

2 take the differential current and terminate the two currents in a pair of resistors (or active loads) connected to the new power supply rails,

3 receive the new signal into a differential receiver

done

Title: Re: Connecting analog power domains in the same chip in ICs (Integrated Circuits)
Post by Tako on Nov 4^th, 2014, 8:38am

loose-electron wrote on Nov 3^rd, 2014, 5:03pm:

Right. Good idea. A differential pair constructed with transistors from 3.3 V domain with resistors connected to 2.5 V domain.

Thanks! :)

Title: Re: Connecting analog power domains in the same chip in ICs (Integrated Circuits)
Post by Tako on Nov 4^th, 2014, 9:02am

As an example of sending an analog signal between two different power domains see Fig. 32 and Fig. 49 here: [link](http://www.ti.com/lit/ds/symlink/afe031.pdf) . The input signal of the PGA1 is 10Vpp while the PGA2 can support input signal equal to its power domain that is 3.3 V. these two PGAs are connected through low-pass filter LPF and capacitor (C10 in Fig. 49).

Title: Re: Connecting analog power domains in the same chip in ICs (Integrated Circuits)
Post by raja.cedt on Nov 4^th, 2014, 1:53pm

Hi Toko,
As jerry pointed out, diff pair based concept is common idea. Think of a serial IO transmitter is communicating with receiver from different vendor.

Thanks,
Raj.