2 Ch. Translator, TTL to NECL


$ 1,130.45


  • Converting TTL/CMOS signals to Differential NECL Signals
  • High Speed Digital Communications system testing
  • High Speed SONET Clock Level Translation
  • Converting TTL/CMOS Clocks to NECL Clocks for connection to Transient Recorders


  • fMAX > 300 MHz
  • 750 ps tr
  • 50 Ω TTL/CMOS Input
  • 1.5 V or 1 V Selectable Input Threshold
  • Complementary NECL Outputs
  • BNC Input Connector
  • SMA or Triax Output Connectors
  • DC-Coupled I/O's
  • Self-contained 1.3 x 2.9 x 3.9-in. units including AC/DC Adapters


The PRL-420ND translator converts TTL/CMOS logic to NECL levels.

Each unit has a switch-selectable 1.5 V or 1.0 V input threshold voltage with a fixed 50 Ω input termination. The complementary NECL outputs from the PRL-420ND are suitable for driving 50 Ω loads terminated to -2 V. The outputs of all units can also drive AC-coupled or floating 50 Ω loads.

These Logic Level Translators are designed specifically for use in testing and interfacing of high speed digital communications circuits, where conversions from TTL/CMOS level signals to NECL level signals are often required. They are ideal building blocks that complement other PRL Logic Level Translators, such as the PRL-450ND, PRL-450PD, PRL-460NPD and PRL-460PND, etc. in systems integration applications where interconnections of mixed logic signals are often necessary.

They are ready-to-use functional modules housed in 1.3 x 2.9 x 3.9-in. extruded aluminum enclosures and are supplied with ±8.5V AC/DC Adapters. The TTL input connector is BNC. The NECL output connectors can be SMA or Triax. Block diagrams is shown in Fig. 1A and 1B.

If mounting is desired, a pair of 35001420 mounting brackets can accommodate two PRL modules of the same length. A number of PRL modules can also share a single ±8.5V AC/DC adapter using the PRL-730 or PRL-735 voltage distribution module.

Fig. 1A, PRL-420ND Block Diagram
Fig. 1B, PRL-420NDTR Block Diagram

(0° C ≤ TA ≤ 35° C)*

Symbol Parameter PRL-420ND Unit
Min Typ Max
Rin Input Resistance 49.5 50 50.5 Ω
Rout Output Resistance NPN emitter Ω
VTOSH Input Threshold Voltage (High) 1.4 1.5 1.6 V
VTOSL Input Threshold Voltage (Low) 0.9 1.0 1.1 V
VOL Output Low Level -1.85 -1.70 -1.55 V
VOH Output High Level -1.0 -0.8 -0.7 V
IDC1 DC Input Current, +8.5 V 35 45 mA
IDC2 DC Input Current, -8.5 V -132 -145 mA
VDC DC Input Voltage ±7.5 ±8.5 ±12 V
VAC AC/DC Adapter Input Voltage 103 115 127 V
tPLH Propagation Delay to output ↑ 1.5 ns
tPHL Propagation Delay to output ↓ 1.5 ns
tr/tf(1) Rise/Fall Times (20%-80%) 750 850 ps
tSKEW Skew: VO↑↔VO 200 500 ps
tSKEW Skew: VO1↑↔ VO2 200 500 ps
Max Clock Frequency
Input Threshold Voltage (High)
200 300 MHz
Max Clock Frequency
Input Threshold Voltage (Low)
300 400 MHz
Size 1.3 x 2.9 x 3.9 in.
Weight, excl. AC adapter 7 Oz
Shipping weight, incl. AC adapter 4 lb.

*Unless otherwise specified, dynamic measurements are made with all outputs terminated into 50 Ω /-2 V for PRL-420ND.


The output rise and fall times are measured with with all inputs terminated into 50 Ω/VTT. For best performance all outputs should be terminated into 50 Ω/VTT or else AC- coupled into 50 Ω loads. If a single output is used, its complement must be terminated; otherwise output waveform distortion will occur. If one pair of complementary outputs is used, the other complementary pair may remain unterminated. Use the PRL-550NQ4X, four channel NECL Terminator, for the 50 Ω/VTT termination and for connection of NECL signals to 50 Ω input oscilloscopes. The PRL-ACT-50, Dual Channel AC-Coupled 50 Ω Terminator, may also be used to provide the 50 Ω/VTT termination. If preservation of DC levels is not required, then the PRL-SC-104, 0.1 µf DC block or a 12 dB AC-coupled attenuator may be used to connect the PECL outputs to 50 Ω input instruments.

(2). fMAX for the PRL-420ND is measured by connecting its inputs to the PRL-450ND, NECL to TTL Logic Level Translator, and its outputs to the ÷2 differential inputs of the PRL-255N NECL frequency divider. The outputs of the PRL- 255N are then measured using the PRL-550NQ4X, four channel NECL Terminator, connected to a 50 Ω input sampling 'scope.

While we believe these models to be accurate, no representations are made as to accuracy or suitability for any application: