Support for ECL / PECL Logic Levels

Knowledge Base Article # Q200134

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Summary Do the GX5280 Series or GX5290 Series Digital I/O products support ECL or PECL levels?
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Instruments that provide PECL interfacing are the GX5050, GX5150 and GX5152, provide they are configured with the GX5940 PECL I/O module.  The GX5280 Series or the GX5290 Series do not have support for PECL.

ECL (Emitter Coupled Logic) and PECL (Positive ECL) are both differential I/O interfaces and are not compatible with single-ended logic families.  ECL logic is designed to work with negative power supply levels, and the normal logic levels for ECL are:
V(OH) = -0.9 V
V(OL) = -1.7 V

The term PECL means we are using ECL logic but with Positive power supply voltages. The normal logic levels for PECL are:
V(OH) = 4.1 V
V(OL) = 3.3 V

The GX5280 and GX5290 series Digital I/O instruments support two types of logic interfaces, Programmable LVTTL and LVDS – except for the GX5291, which supports only Programmable LVTTL levels.  Neither LVTTL nor LVDS are compatible with ECL or PECL logic.

LVTTL is a single ended I/O standard with output levels programmable in the range of:
Min:  1.4V
Max:  3.6V
This is compatible with TTL/LVTTL/CMOS/LVCMOS logic families.  
The input thresholds for the LVTTL interface is selectable:
1.5 V, 1.8V, 2.5V, or 3.3 V (all are 5V tolerant)

LVDS is a differential signal, similar to ECL and PECL, but the levels are incompatible with either ECL or PECL.  The levels for LVDS/LVDM/M-LVDS are:
Differential Output Voltage:
480mV (Min.); 650mV (Max.)
Input Threshold:
Positive going threshold: 50mV (Max.)
Negative going threshold: -50mV (Min.)
Input voltage hysteresis: 25mV (Typ.)
Article Date 3/25/2009
Keywords GX5280 Series, GX5290 Series, GX5050, GX5150, GX5152, ECL, PECL, LVTTL, LVDS, Logic Levels

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