NECL logic levels are offset from ground. Without proper level shifting, these logic signals can not be connected to ground-referenced 50 Ω input instruments, such as sampling 'scopes, network analyzers, scanners and counters, etc. Otherwise, either the NECL equipment outputs or the measurement instrument inputs may be made inoperative or damaged.
When driving a length of 50 Ω coaxial cable, a NECL output must be terminated into a 50 Ω load that is connected to a terminating voltage VTT = VCC -2 V. For NECL circuits operating with a supply voltage of either -5.2 V or -4.5 V, VCC is 0 V, and VTT is equal to -2 V.
NECL Terminators are level translators which convert NECL signals into signals that can be connected to ground referenced 50 Ω input instruments and, at the same time, provide standard 50 Ω/VTT terminations required by NECL signals.
The PRL-550NQ4X is a Four Channel NECL Terminator designed to interface with NECL circuits operating with a -5.2 V or -4.5 V supply. Each input has an equivalent 50 Ω resistor terminated to a voltage VTT = -2 V.
The outputs of these Terminators are designed for direct connection to ground-referenced 50 Ω input instruments as shown in Fig. 1, and a block diagram is shown in Fig. 2. These near-ground level output signals* protect sensitive instruments and enhance measurement accuracy when these instruments are used.
Once a NECL signal is translated through a proper Terminator, it can be routed through 50 Ω scanners and other high frequency measuring instruments for processing. Each PRL-550NQ4X Terminator is housed in an attractive 1.3 x 2.9 x 2.2-in. extruded aluminum enclosure and is supplied with a ±8.5 V AC/DC Adapter.
(0° C ≤ TA ≤ 35° C)*
|VTT||Input Termination Voltage||-2.2||-2.0||-1.8||V|
|VOS||Output Offset Voltage*||-20||0||20||mV|
|IDC1||DC Input Current, +8.5 V||+60||+85|
|IDC2||DC Input Current, -8.5 V||-125||-150|
|VDC||DC Input Voltage||±7.5||±8.5||±12||V|
|VAC1||AC/DC Adapter Input Voltage, 120 V||103||115||127||V|
|tPLH||Propagation Delay to output ↑||475||575||ps|
|tPHL||Propagation Delay to output ↓||475||575|
|tSKEW||Skew between outputs||20||50||ps|
|Channel-to-Channel Cross Talk @ 1.4 GHz||34||40||dB|
|Size||1.3 x 2.9 x 2.2||in.|
|Weight, excluding AC adapter||5||Oz|
|Shipping weight, including AC adapter||4||lb.|