application of oscilloscopes to metrology at...
TRANSCRIPT
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