Application of Oscilloscopes to Metrology at NPL

Matthew HarperNational Physical Laboratory,

Teddington, Middlesex TW11 0LW, UK

27th ANAMET Meeting 10th April 2007

Ultrafast work at NPL

• Calibration of sampling and real-time oscilloscopes– Rise-time and frequency domain– Non-linearity and timebase issues

• Calibration of pulse generators and oscilloscope calibrators– Rise-time and aberrations

• Calibration of photodiodes and photoreceivers• Power meter rise-time measurements• Jitter measurement and correction• Modulated signal measurements• Connection and delay characterisation

Main focus: scope-based techniques

• Oscilloscope & pulse generator calibration – EOS calibration system

• Timebase corrections – IQ technique

• Oscilloscope & pulse generator calibration – EOS calibration system

••• Timebase corrections Timebase corrections Timebase corrections ––– IQ techniqueIQ techniqueIQ technique

Oscilloscope Calibration

Oscilloscope calibrates pulse generator

Pulse Generator calibrates oscilloscope

Electro-Optic Effect

E∝∆θ

EOS bandwidth is > 600 GHz

Photoconductive Pulse Generator

GaAs substrate

Lt-GaAs epilayer

Bias Voltage

Au metallisation

Pulses generated are < 1ps

Electro-Optic Sampling System

Ti:Sapphire

OscilloscopeFliter & AmplifierSi photodectors

Function generator

AOM

Lock-in Amplifier

Optoelectronic Calibration of Oscilloscope

EOS calibrates optically-generated

pulse

Optically-generated pulse calibrates

oscilloscope

Oscilloscope calibrates pulse generator

Optoelectronic Calibration of Pulse Generator

Pulse Generator calibrates oscilloscope

EOS calibrates generator

Traceability chain

NPL calibrated devices

EOS

Customer calibrated

devices (e.g. standards

labs)

End users

Main focus of talk

••• Oscilloscope & pulse generator calibration Oscilloscope & pulse generator calibration Oscilloscope & pulse generator calibration ––– EOS EOS EOS calibration systemcalibration systemcalibration system

• Timebase corrections – IQ technique

Principle of technique

Optical Sampling gate 1

Sampling gate 2

Sampling gate 3

Sampling gate 4

Trigger input

Sampling oscilloscope

Sampling gate 1

Sampling gate 2

Sampling gate 3

Sampling gate 4

Trigger inputTrigger

Signal A

Signal B

Signal C

Signal D

Jitter gate << Jitter trigger

Principle of the technique

Obtain the phase information

⎟⎟⎠

⎞⎜⎜⎝

⎛=

2

1argref

ref

AmpAmp

Phase Corrected timing of another waveform

0 1 2 3 4 5 61

0.5

0

0.5

1

Points

corr

ecte

d IQ

Sig

nals

Correction of waveform

• Two sinusoidal signals in quadrature allow sample time to be determined

• Determines timing of waveform measured in other channel

Experimental layout

Optical Sampling gate 1

Sampling gate 2

Sampling gate 3

Sampling gate 4

Trigger input

Sampling oscilloscope

Sampling gate 1

Sampling gate 2

Sampling gate 3

Sampling gate 4

Trigger input

90° Hybrid splitter

90° Hybrid splitter

I signal

Q signalReference signal

Trigger signal

Measured signal

IQ errors

Two identical signals, one in phase (I) the other in

quadrature (Q)

Plotted parametrically, a circle is produced

IQ errors

Errors in offset, phase and amplitude will be present

These distort, translate and rotate the circle

IQ errors

In real systems there will also be noise present

Noise ‘thickens’ the parametric plot

Error correction

A

A

Pulse application

Without timebase jitter compensation

79 mUI p-p

With timebase jitter compensation

38 mUI p-p

RF application

10 MHz Reference

Sampling gate 1

Sampling gate 2

Sampling gate 3

Sampling gate 4

Trigger input

Synthesizer 1

90° Hybrid splitter

Synthesizer 2

Sampling gate 1

Sampling gate 2

Sampling gate 3

Sampling gate 4

Trigger input

Synthesizer 160 GHz

90° Hybrid splitter

Synthesizer 2

Sampling oscilloscope

10 GHz

RF application

RF waveform correction

Datacomms application

Eye diagram correction

Ultrafast work at NPL

• Calibration of sampling and real-time oscilloscopes– Rise-time and frequency domain– Non-linearity and timebase issues

• Calibration of pulse generators and oscilloscope calibrators– Rise-time and aberrations

• Calibration of photodiodes and photoreceivers• Power meter rise-time measurements• Jitter measurement and correction• Modulated signal measurements• Connection and delay characterisation