PAL SYSTEM TELEVISION MEASUREMENT :NONLINEAR DISTORTIONS

III. NONLINEAR DISTORTIONS

Amplitude dependent waveform distortions are often referred to as nonlinear distortions. This
classification includes distortions that are dependent on APL (Average Picture Level) changes and/or instantaneous signal level changes.
Since amplifiers and other electronic circuits are linear over only a limited range, they may tend to compress or clip large signals. The result is nonlinear distortion of one type or another.
Nonlinear distortions may also manifest themselves as crosstalk and intermodulation effects between the luminance and chrominance portions of the signal.
The first three distortions discussed in this section are differential phase, differential gain, and luminance nonlinearity.
These are by far the most familiar and most frequently measured nonlinear distortions.
These parameters are included in the performance specifications of most video equipment and are regularly evaluated in television facilities. The other distortions are not as routinely tested, however, most measurement
standards and performance checks include them.
It is generally recommended that nonlinear distortions be measured at different average picture levels. Some test s i g n a l generators provide variable APL signals by combining the test signal with a variable level
pedestal. Since in-service measurements cannot be made with these test signals, measurements requiring control of APL are often eliminated from routine testing.

Lihat juga

Table of Contents

Preface	3
Good Measurement Practices	4
EQUIPMENT REQUIREMENTS	4
CALIBRATION	6
INSTRUMENT CONFIGURATION	6
DEMODULATED RF SIGNALS	8
TERMINATION	8
DEFINITION OF THE PAL TELEVISION STANDARD	8
PERFORMANCE GOALS	8
Waveform Distortions and Measurement Methods	9
I VIDEO AMPLITUDE AND TIME MEASUREMENTS	9
Amplitude Measurements	10
Time Measurements	12
SCH Phase	15
II LINEAR DISTORTIONS	18
Chrominance-to-Luminance Gain and Delay	19
Short Time Distortion	24
Line Time Distortion	26
Field Time Distortion	28
Long Time Distortion	30
Frequency Response	31
Group Delay	36
K Factor Ratings	38
III NONLINEAR DISTORTIONS	41
Differential Phase	42
Differential Gain	46
Luminance Nonlinearity	50
Chrominance Nonlinear P h a s e	5 2
Chrominance Nonlinear Gain	5 3
Chrominance-to-Luminance Intermodulation	54
Transient Sync Gain Distortion	55
Steady-State (Static) Sync Gain Distortion	56
IV NOISE MEASUREMENTS	57
Signal-to-Noise Ratio	58
V TRANSMITTER MEASUREMENTS	6 0
ICPM	61
Depth of Modulation	63
GLOSSARY OF TELEVISION TERMS	64
APPENDICES
APPENDIX A - PAL COLOUR BARS	67
APPENDIX B - SINE-SQUARED PULSES