Comparators/Sinewave Converters

Applications
  • Window Comparators
  • High Speed Timing
  • Line Receivers
  • Threshold Detection
  • Peak Detection
  • Sinewave to square wave conversion

Stand alone Hi-speed dual channel Comparator modules from Pulse Research Lab detect sinewave and small signals (as small as 10 mV) and convert them to logic-level outputs. PRL offers models with complementary TTL, NECL, LVPECL, or RS-422 outputs, and two different sets of input thresholds.

All models have an input voltage threshold selectable by toggle switch, with a positive voltage threshold, a negative voltage threshold, and a "zero-crossing" threshold. Zero-crossing is best for converting AC-coupled sinewaves.

When the input signal (blue, in the image below) exceeds the internal voltage threshold (red), the output (green) will transition to a logic High. Otherwise the output will be at a logic Low.

Two sets of voltage thresholds are available:

  • Standard ±50 mV thresholds, best for converting sensor outputs, weak photodiode outputs, or heavily attenuated pulses.
  • ±400 mV pulses, best for Fast Negative NIM signals (-400 mV), non-standard logic, noisy sensor outputs, or sinewaves that are offset from ground  

The input threshold voltage can also be varied independently in each channel by applying an external DC bias voltage or shunt resistor to the D input.

  • If the external DC bias has a sufficiently low output impedance, it will over-ride the internally-generated VTH, and the toggle switch setting is a don’t-care.
  • For an external shunt resistor, the effective threshold voltage, VTHE, will be the result of the resistor-divider network formed by the external shunt resistor and the internal 50 Ohm termination to the selected VTH.
  • In the following example, the internal VTH is set to +50 mV, and it is pulled down to an effective VTHE of +10 mV via a 12.5 Ω shunt resistor:

 

Model Input Threshold Levels (Selectable) Output Levels
Positive 0 Negative
PRL-350ECL +50 mV 0 V -50 mV NECL
PRL-350ECL-NIM +400 mV 0 V -400 mV* NECL
PRL-350LP +50 mV 0 V -50 mV LVPECL
PRL-350LP-NIM +400 mV 0 V -400 mV* LVPECL
PRL-350NIM +50 mV 0 V -50 mV NIM
PRL-350RS +50 mV 0 V -50 mV RS422
PRL-350TTL +50 mV 0 V -50 mV TTL
PRL-350TTL-NIM +400 mV 0 V -400 mV* TTL

 

* voltage equivalent for Fast Negative NIM in a 50 Ohm environment. 

The PRL-255CN is a frequency divider (f/2 and /f4) with the same input circuit as the PRL-350 Series, and can divide sinewaves or small-amplitude signals.

Please see our Sinewave Conversion FAQ for other models that can convert sinewaves (200 mV min amplitude)