| Author |
Message |
gja
Guest
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 Posted:
Wed Dec 15, 2004 4:40 am Post subject:
Virtex2 I/O standards |
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For Virtex II parts, I see that the Vih and Vil levels are the same for
LVTTL and LVCMOS33, my question is are the input structures really different
or are they the same for the two standards. Also, are the output structures
for LVTTL the same as LVCMOS33, since both Vol are the same, and LVTTL Voh
is a subset of LVCMOS33 Voh. |
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Austin Lesea
Guest
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| Posted:
Wed Dec 15, 2004 9:09 pm Post subject:
Re: Virtex2 I/O standards |
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gja,
All single ended non reference voltage standards use the same schmidt
trigger single ended input circuit.
All single ended reference voltage standards use the same differential
comparator which has one input tied to Vref.
All differential input standards use the same differential comparator
(different that the single ended Vref one above).
These three input circuits are selected by the type of standard chosen,
and are designed to operate over the range of the Vcco voltages used,
and designed to meet all input standards stated.
The actual specifications obviously exceed (are better than) what is
required by a standard, as the circuits have to do all of the jobs, over
all process, voltage, and temperature corners.
The published specifications are those of the standards, as publishing
anything else would confuse those who don't understand how to interpret
the specifications (like some purchasing agents or component engineers
who mindlessly compare us to our competition).
Austin
gja wrote:
| Quote: | For Virtex II parts, I see that the Vih and Vil levels are the same for
LVTTL and LVCMOS33, my question is are the input structures really different
or are they the same for the two standards. Also, are the output structures
for LVTTL the same as LVCMOS33, since both Vol are the same, and LVTTL Voh
is a subset of LVCMOS33 Voh.
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gja
Guest
|
| Posted:
Wed Dec 15, 2004 11:41 pm Post subject:
Re: Virtex2 I/O standards |
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Austin, thank you very much for your response. You may have addressed it,
but it was not clear to me, what about the output structures that were the
second part of my question? Are LVTTL output structures the same as LVCMOS33
?
"Austin Lesea" <austin@xilinx.com> wrote in message
news:cppnj8$8g81@cliff.xsj.xilinx.com...
| Quote: | gja,
All single ended non reference voltage standards use the same schmidt
trigger single ended input circuit.
All single ended reference voltage standards use the same differential
comparator which has one input tied to Vref.
All differential input standards use the same differential comparator
(different that the single ended Vref one above).
These three input circuits are selected by the type of standard chosen,
and are designed to operate over the range of the Vcco voltages used,
and designed to meet all input standards stated.
The actual specifications obviously exceed (are better than) what is
required by a standard, as the circuits have to do all of the jobs, over
all process, voltage, and temperature corners.
The published specifications are those of the standards, as publishing
anything else would confuse those who don't understand how to interpret
the specifications (like some purchasing agents or component engineers
who mindlessly compare us to our competition).
Austin
gja wrote:
For Virtex II parts, I see that the Vih and Vil levels are the same for
LVTTL and LVCMOS33, my question is are the input structures really
different
or are they the same for the two standards. Also, are the output
structures
for LVTTL the same as LVCMOS33, since both Vol are the same, and LVTTL
Voh
is a subset of LVCMOS33 Voh.
|
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Austin Lesea
Guest
|
| Posted:
Thu Dec 16, 2004 12:05 am Post subject:
Re: Virtex2 I/O standards |
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gja,
Sorry. Hit 'enter' too soon.
Yes, the output structures are all identical: just select the number of
pull down nmos devices, and the number of pull up pmos devices required
for a given interface standard.
Austin
gja wrote:
| Quote: | Austin, thank you very much for your response. You may have addressed it,
but it was not clear to me, what about the output structures that were the
second part of my question? Are LVTTL output structures the same as LVCMOS33
?
"Austin Lesea" <austin@xilinx.com> wrote in message
news:cppnj8$8g81@cliff.xsj.xilinx.com...
gja,
All single ended non reference voltage standards use the same schmidt
trigger single ended input circuit.
All single ended reference voltage standards use the same differential
comparator which has one input tied to Vref.
All differential input standards use the same differential comparator
(different that the single ended Vref one above).
These three input circuits are selected by the type of standard chosen,
and are designed to operate over the range of the Vcco voltages used,
and designed to meet all input standards stated.
The actual specifications obviously exceed (are better than) what is
required by a standard, as the circuits have to do all of the jobs, over
all process, voltage, and temperature corners.
The published specifications are those of the standards, as publishing
anything else would confuse those who don't understand how to interpret
the specifications (like some purchasing agents or component engineers
who mindlessly compare us to our competition).
Austin
gja wrote:
For Virtex II parts, I see that the Vih and Vil levels are the same for
LVTTL and LVCMOS33, my question is are the input structures really
different
or are they the same for the two standards. Also, are the output
structures
for LVTTL the same as LVCMOS33, since both Vol are the same, and LVTTL
Voh
is a subset of LVCMOS33 Voh.
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