What's the difference between LVCMOS, LVTTL and LVDS?

[satishkumar]

Hi All,

Anyone please explain LVCMOS,LVTTL,LVDS. advantages,difference.

 

[vinod_g]

lvttl lvcmos

Each one as different advantages and applications

LVDS --
Low-voltage differential signaling, or LVDS, is an electrical signaling system that can run at very high speeds over cheap, twisted pair copper cables.
LVDS is a differential signaling system, which means that it transmits two different voltages which are compared at the receiver. LVDS uses this difference in voltage between the two wires to encode the information.
The low common-mode voltage (the average of the voltages on the two wires) of about 1.25 V allows LVDS to be used with a wide range of integrated circuits with power supply voltages down to 2.5 V or lower.

LVCMOS--
Fabrication is simple than LVTTL
Low power dissipation
Good noise immunity/margin
Occupies less area when compare to Bipolar


And last small suggestion---- you have to browse Internet for gaining good knowledge on them.....

 

[venkatesankalidass]

lvcmos lvttl

see this


Voltage Levels Description:
Comparison of Input and Output [I/O] logic switching levels for the CMOS, TTL, mixed CMOS/TTL, ETL, BTL, GTL, and Low voltage glue logic families. The graph above provides a comparison between the Input and Output [I/O] logic switching levels for CMOS, and TTL logic families. The graph shows 5 volt CMOS, TTL, and mixed CMOS/TTL IC devices, and 3.3 volt LVTTL LVCMOS IC devices. BTL and GTL [Bus Driver] IC are shown for comparison. Note many Low Voltage [LV] CMOS families are 5 volt tolerant [not damaged by applying 5v to the input pins]. The output logic levels above are defined by the Terms section below. For a review of Noise Margin numbers and a short description of many of the IC logic families , refer to the Logic Family Selection page. A graph for Low Voltage [LV] devices resides on the LV Logic Threshold page. An additional chart of Interface bus threshold levels is provided on the Interface Threshold Voltage Level page.
The GTLP switching levels [not shown above] follows; Output-Low is less-then 0.5v, Output-High is 1.5v, and the receiver threshold is 1.0 volts.

The CMOS families [74ACxx, 74HCxx, 74AHCxx, and 74Cxx] have different input and output switching levels than the TTL logic devices [74Fxx, 74Sxx, 74ASxx, 74LSxx, and 74ALSxxx]. The output switching levels from CMOS ICs is higher then a TTL IC, which happens to result in a better design and does not have a negative effect. However the difference in input logic switching level does impact your design, the TTL output does not correctly switch a CMOS input. The switching difference between a TTL IC output and a CMOS IC input has to be accounted for. The mixed CMOS/TTL [74ACTxx, 74HCTxx, 74AHCTxx, and 74FCTxx] logic devices have TTL logic input switching levels and CMOS output switching levels. The mixed TTL/CMOS devices are CMOS devices which just happen to have TTL input trigger levels, but they are CMOS ICs.

So the rule is, if you use a CMOS IC for reduced current consumption [for example], and a TTL IC feeds the CMOS chip, then you need to either provide a voltage translation or use one of the mixed CMOS/TTL devices [which have a "T" in the part number].

Side Note: I used 74xx part numbers above. The 74xx families [or just 74 prefix] refer to a commercial operating temperature range. A 54xx part number [or just 54 prefix] may also be found which refers to a military operating temperature range. Some 74xx device families may also work at the Industrial temperature range [but you have to check, there is no hard and fast rule]. So a 74xx244 works at a commercial operating temperature, while a 54xx244 which is the same device [maybe the same pinout, and package] will continue to operate to the military operating temperature range [which is wider]. The difference in operational temperature ranges is provided on the Logic Prefix page.

Terms -
VCC: The voltage applied to the power pin(s). In most cases the voltage the device needs to operate at.
VIH: [Voltage Input High] The minimum positive voltage applied to the input which will be accepted by the device as a logic high.
VIL: [Voltage Input Low] The maximum positive voltage applied to the input which will be accepted by the device as a logic low.
VOL: [Voltage Output Low] The maximum positive voltage from an output which the device considers will be accepted as the maximum positive low level.
VOH: [Voltage Output High] The maximum positive voltage from an output which the device considers will be accepted as the minimum positive high level.
VT: [Threshold Voltage] The voltage applied to a device which is "transition-Operated", which cause the device to switch. May also be listed as a '+' or '-' value.

Description of TTL, ECL and CMOS Glue Logic Families