JPH0379162A - Vertical oscillation circuit - Google Patents

Abstract

PURPOSE:To reduce secular change due to a capacitor by generating a satisfactory sawtooth wave with linearity. CONSTITUTION:A horizontal synchronizing signal (a) and a vertical synchronizing signal (b) are inputted to a phase locked loop(PLL) circuit 1, and a clock pulse signal (c) and a reset pulse signal (d) are obtained, then, they are inputted to a counter 2. The counter 2 inputs output (g) to a ROM 3, and the field signal (e) of the PLL circuit 1 is inputted to the least significant bit of the ROM 3. Data of sawtooth wave is written on the ROM 3, and output data (h) is outputted as a step shape sawtooth wave via a D/A converter 4. At a first field and a second field, step shape waves with different size only by one LSB can be obtained by reading out the data of the odd address of the ROM 3 at a first field and the data of the even address at a second field with the field signal (e) to be inputted to the ROM 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a vertical deflection circuit for equipment that displays television video signals, such as a projection type projector.

[Prior art]

Automatic oscillation circuit 5 consisting of the transistor or IC circuit shown in Fig. 3 and a time constant circuit of a capacitor and resistor (CR).
Using the charging and discharging characteristics of the capacitor 6, a sawtooth wave F for vertical deflection is generated using the input vertical synchronization signal S as a trigger signal. However, due to the charging and discharging characteristics of the capacitor 6, the linearity and stability of the sawtooth wave change over time.

[Problem to be solved by the invention]

The present invention has been made in view of the conventional example, and an object thereof is to reduce changes over time caused by a capacitor and to improve the linearity and stability of a sawtooth wave for vertical deflection.

[Failure to solve the problem]

The present invention is characterized in that it generates a sawtooth wave for vertical deflection with excellent linearity and stability that does not change over time using digital signal processing consisting of a phase-locked loop (PLL) circuit and a digital oscillation circuit. be.

[Effect]

1 and 2, a phase-locked loop (PLL) circuit 1 generates a clock pulse signal C synchronized with a horizontal synchronization signal a, a reset pulse signal d synchronized with a vertical synchronization signal d, and a field signal e; , a counter 2. which operates with the same clock pulse signal C and the same reset pulse signal d.
Read-only memory (ROM)3. It consists of a digital oscillation circuit consisting of a digital/analog converter 4.

The counter 2 counts the clock pulse signal C and outputs the value to the address of the ROM 3. The field signal e output from the PLL circuit 1 is input to the least significant bit (LSB) of the address in the ROM 3, and the output data h from the ROM 3 is converted into a sawtooth wave f through the digital/analog converter 4.
Output.

〔Example〕

As shown in FIG. 1, a horizontal synchronization signal a and a vertical synchronization signal S obtained by passing a composite video signal through a synchronization separation circuit (not shown) are input to a phase-locked loop (PLL) circuit 1.
A circuit 1 inputs a clock pulse signal C and a reset pulse signal d synchronized with a horizontal synchronizing signal a and a vertical synchronizing signal S, respectively, to a counter 2. The counter 2 counts the same 9-bit tallock pulse signal C, inputs its output data g to the address of the read-only memory (ROM) 3, and simultaneously inputs the field signal e output from the PLL circuit 1 to the highest address of the ROM 3. Input to the lower bit (LSB). Data of a sawtooth wave that goes around in 525 lines corresponding to the NTSC system is written in the ROM 3, and the 10-bit output data h of the ROM 3 is passed through the digital/analog converter 4 to create a step wave sawtooth wave for vertical deflection. It is output as a wave f and connected to a vertical deflection output circuit (not shown) in the subsequent stage. Note that the field signal e input to the address register SB of ROM3 outputs an H level in the first field and an L level in the second field, as shown in Figure 2e. By reading data at odd addresses in ROM3 and reading data at even addresses in the second field, the first and second fields in FIG.
This results in staircase waves with different sizes, resulting in interlaced scanning.

〔Effect of the invention〕

As described above, the present invention utilizes a phase-locked loop (PLL) circuit, a counter, a read-only memory (ROM), and a digital oscillator circuit consisting of a digital/analog converter to achieve good linearity for vertical deflection without changes over time. By generating a sawtooth wave, it is possible to improve the vertical linearity and stability of a deflection circuit of a projector or the like, where deflection distortion becomes more noticeable as the screen becomes larger.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the vertical oscillation circuit of the present invention, FIG. 2 is an operation waveform diagram of FIG. 1, and FIG. 3 is a block diagram of a conventional vertical oscillation circuit. 1 is a phase-locked loop circuit, 2 is a counter, 3 is a read-only memory, 4 is a digital/analog converter, C is a clock pulse signal synchronized with the horizontal synchronization signal, d is a reset pulse signal synchronized with the vertical synchronization signal, e is a field signal.

Claims (1)

[Claims] In equipment that displays television video signals, a horizontal synchronization signal and a vertical synchronization signal are connected to a phase-locked loop circuit, and a clock pulse signal synchronized with the horizontal synchronization signal and a reset pulse synchronized with the vertical synchronization signal are output from the phase-locked loop circuit. The output data of the counter and the field signal output from the phase-locked loop circuit are connected to a read-only memory, and the output data of the read-only memory is connected to a digital/analog converter. A vertical oscillation circuit that outputs a sawtooth wave for vertical deflection that does not change over time from a digital/analog converter.