U.S. Philips Corporation

U.S. Phillips Corporation

Jozef J Hulshof

Dirk J Teuling

Henricus L Simons

In the market, there is a tendency towards picture tubes with a super flat screen. Due to the flat screen, it is becoming increasingly difficult to meet the even tighter specification on North/South raster distortion (N/S distortion), the tighter specification being caused by a growing importance of text display and high resolution displays. A deflection correction circuit is provided which compensates for a N/S distortion by inducing a correction current (Icv) through a vertical deflection coil (Lv). The correction current (Icv) can be injected in the vertical deflection coil (Lv) via an injection transformer (Ti) coupled in series with the vertical deflection coil (Lv). The injection transformer (Ti) is driven via an output stage (3) by a waveform generator (1,2). The waveform generator (1,2) generates a voltage waveform (M) built up out of substantially straight line sections. The deflection coil (Lv) integrates the voltage waveform (M) into a current waveform (Icv) having substantially parabolic sections. Such an inexpensive and flexible deflection correction circuit can be used to compensate for top/bottom and/or seagull N/S distortion, or for correction of convergence distortions. The deflection correction circuit can be a discrete or an integrated circuit.

Deflection correction

In order to cause scan and/or fly-back voltages (Vsca, Vfly) supplied by a horizontal output stage (1) to vary at a desired rate during a change of state in a horizontal deflection circuit (1, 2, 4), a feedback circuit (4) is provided. This feedback circuit (4) processes the scan and/or fly-back voltages (Vsca, Vfly) to a control voltage (Vco) with which a duty cycle (dc) of a drive signal (Hdr) of a switching element (Tr) in the horizontal output stage (1) is influenced.

Horizontal deflection

A line sychronizing circuit in a picture display device, has a phase control loop including an oscillator and a phase comparison stage. In order to enlarge the capture range of the control loop, the phase comparison stage is in the form of a phase-frequency detector having a trigger action on edges of pulses applied, the circuit being provided with means for inhibiting the supply of the control signal form the phase-frequency detector during a predetermined period after establishing that the phase difference measured by the phase-frequency detector between the local line-frequency signal and the incoming line synchronizing signal is larger than a predetermined value. In the perdetermined period, the oscillator signal has substantially the same frequency as before establishing that the phase difference measured by the phase frequency detector is larger than the predetermined value. The supply of the control signal is restored during a second predetermined period after the supply of the control signal has been inhibited, and this irrespective of the phase difference between the local line signal and the incoming line synchronizing signal.

Line synchronizing circuit in a picture display device

A circuit for supplying a periodic, essentially parabolic signal by squaring a sawtooth-shaped signal. For eliminating a disturbance occurring during the retrace period, a signal is generated during this period whose polarity is opposite to that of the parabolic signal occurring during the trace period, both the generated signal and the derivative with respect to time of this signal assuming values at the start and end of the retrace period which are substantially equal to the corresponding values at the same instants of the essentially parabolic signal occurring during the trace period, and of the derivative with respect to time of this signal.

Circuit for producing a periodic, essentially parabolic signal

A line deflection circuit in a picture display device in which a bidirectional supply switch controlled at the line frequency, as inductance and a bidirectional deflection switch likewise controlled at the line frequency are arranged in series between the terminals of a supply voltage source. A line deflection resonant network is connected to the deflection switch. By means of a forward control of the period of conductance of the supply switch the amplitude of the line deflection current is changed at the field frequency and by means of a feedback control of the said period this amplitude is maintained constant during a time interval which is short with respect to the duration of a field period. The line amplitude is substantially independent of the value of the line frequency and the trace capacitor is switchable as a function of the line frequency.

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Eindhoven, Netherlands

Jozef J Hulshof