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.
Virtex2 I/O standards
Started by ●December 15, 2004
Reply by ●December 15, 20042004-12-15
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. > >
Reply by ●December 15, 20042004-12-15
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 reallydifferent> > or are they the same for the two standards. Also, are the outputstructures> > for LVTTL the same as LVCMOS33, since both Vol are the same, and LVTTLVoh> > is a subset of LVCMOS33 Voh. > > > >
Reply by ●December 15, 20042004-12-15
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:> 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. >>> >>> > > >
