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Applying IO standards that do not use CMOS transistors

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sharanbr

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Hi,

Some of the IO standards (e.g. CML) actually do not use CMOS transistors inside their IO buffers. Since most of the FPGAs are follow CMOS technology and they also support these IO standards, how are these actually supported?

Of course, the same question would apply even to ASICs also since most of them will be using CMOS technology.

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jbeniston

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sstl iostandard

sharanbr said:
Hi,
Some of the IO standards (e.g. CML) actually do not use CMOS transistors inside their IO buffers.,
I'm not sure this statement is correct. I'm not an expert, but I think it would be more correct to say no static CMOS gates are used. CML uses the same physical CMOS transistors as for static CMOS logic, just they never go in to saturation - which is where static gates spend most of their time.
 

sharanbr

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io standards

Actually my question was a bit generic while you picked up a specific example and answered. So let me rephrase -
Most of the FPGAs actually support almost all the IO standard types available.
So can I assume that these are all designed using CMOS?
Also, some of the IO standards might rely on the underlying transistor technology to give the specified characteristics ...
 

iwpia50s

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io standard

I think to answer your question, (CMOS) Complementary-Metal–Oxide–Semiconductor is simply using an nmos and pmos transistor in complementary mode for on-off switching of logic cells. An IO buffer can be designed in a CMOS process, but the transistors are arranged to achieve different IO standard functions.
 

sharanbr

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jesd8c

I am not sure if I communicated well enough ...
Basically I am talking about few IO standards which obviously seem to use non-cmos logic. One such example is LVTTL. We know that TTL uses BJT as the underlying transistors (thats what classical description for TTL logic shows). We also know that FPGAs support LVTTL as one of their IO types. Now the question is when these FPGAs are fabricated using CMOS, how is that they are able to provide LVTTL as IO type

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mikersia

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iostandard

CML, LVTTL, PECL, SSTL, ... and etc are relaited to electrical parameters of IO standard,- e.g. input thresholds value.
It does'n concerns a method of realization. They can be realized inside IC implemented in pure CMOS technology, or BiCMOS, or Bipolar, or SOI, or ...
 

sharanbr

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iostandard jedec

Most of the IO standard names, I do agree. But TTL has traditionally been used to mean BJT transistors. So I am thinking what the standard committee had in mind when they named LVTTL, when it is well known that such IO characteristics needs to be provided by other transistor technologies also.

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mikersia

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soi io switching concerns

To have clear understanding please see JEDEC standard JESD8C,-
"Interface Standard for Nominal 3V/3.3V Supply Digital Integrated Circuits":
...
1 Scope
... The specifications in this standard represent a minimum set ... of interface specifications for LVTTL compatible and LVCMOS compatible circuits.
...
 

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