Development of a High-Speed Digitizer to Time Resolve Nanosecond Fluorescence Pulses

 

E. Moreno-García*¹, R. Galicia-Mejía², D. Jiménez-Olarte³, J. M. de la Rosa-Vázquez⁴, S. Stolik-Isakina⁵

 

^1,3 Laboratorio de Instrumentación Electrónica, ESFM-IPN, Edificio No.9, U.P. "Adolfo López Mateos", 07630 México D.F., Tel. 5729 6000 ext. 55007 *emoreno@esfm.ipn.mx.

^2,4,5 Laboratorio de Láseres. SEPI-ESIME, IPN, Edificio No.5, U.P. "Adolfo López Mateos", 07630 México D.F., Tel. 5729 6000 ext. 54622.

 

Abstract

The development of a high-speed digitizer system to measure time-domain voltage pulses in nanoseconds range is presented in this work. The digitizer design includes a high performance digital signal processor, a high-bandwidth analog-to-digital converter of flash-type, a set of delay lines, and a computer to achieve the time-domain measurements. A program running on the processor applies a time-equivalent sampling technique to acquire the input pulse. The processor communicates with the computer via a serial port RS-232 to receive commands and to transmit data. A control program written in LabVIEW 7.1 starts an acquisition routine in the processor. The program reads data from processor point by point in each occurrence of the signal, and plots each point to recover the time-resolved input pulse after n occurrences. The developed prototype is applied to measure fluorescence pulses from a homemade spectrometer. For this application, the LabVlEW program was improved to control the spectrometer, and to register and plot time-resolved fluorescence pulses produced by a substance. The developed digitizer has 750 MHz of analog input bandwidth, and it is able to resolve 2 ns rise-time pulses with 150 ps of resolution and a temporal error of 2.6 percent.

Keywords: nanosecond pulses, digitizer, time-equivalent sampling, time-resolved fluorescence.

 

Resumen

En este trabajo se presenta el desarrollo de un sistema digitalizador de alta velocidad para medir en el dominio del tiempo pulsos de voltaje del orden de nanosegundos. El diseño del digitalizador incluye un procesador digital de señales de alto rendimiento, un convertidor analógico digital tipo flash con ancho de banda grande, un conjunto de líneas de retardo, y una computadora para realizar las mediciones en el dominio del tiempo. El procesador ejecuta un programa que aplica una técnica de muestreo en tiempo equivalente para adquirir el pulso de entrada. El procesador se comunica con la computadora vía un puerto serie RS-232 para recibir comandos y transmitir datos. Se desarrolló un programa de control en LabVIEW 7 para iniciar una rutina de adquisición en el procesador. El programa lee datos del procesador punto por punto en cada ocurrencia de la señal, y grafica cada punto para recuperar el pulso de entrada resuelto en tiempo después de n ocurrencias. El prototipo desarrollado se aplica para medir pulsos de fluorescencia provenientes de un espectrómetro. Para esta aplicación se amplió el programa en LabVIEW para controlar el espectrómetro, y para registrar y graficar pulsos de florescencia resuelta en tiempo producidos por una substancia. El digitalizador desarrollado tiene un ancho de banda de 750 MHz en su entrada analógica, y es capaz de resolver pulsos con tiempo de subida de 2 ns con una resolución de 150 ps y un error temporal de 2.6 percent.

 

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