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LM1295 データシート(PDF) 7 Page - National Semiconductor (TI) |
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LM1295 データシート(HTML) 7 Page - National Semiconductor (TI) |
7 / 11 page Circuit Description (Continued) VERTICAL OSCILLATOR The vertical oscillator is an injection-locked ramp generator with automatic level control. The automatic level control maintains the oscillator output ramp height with changes in input frequency. The oscillator requires negative-going TTL level vertical sync pulses, wider than 200 ns, to lock. In the absence of vertical sync, the oscillator runs at free-run fre- quency. The vertical output amplitude is controlled by a volt- age between 0V and 4V on the V Height input with a range of about 1.8 to 1, and by a voltage between 3V and 4V on the Vertical Dynamic Height input with a range of about 1.3 to 1. The control bandwidth of the V Height input is low due to the automatic level control, but that of the Vertical Dynamic Height is greater than 125 kHz. The oscillator has a circuit, requiring an external capacitor, 2f Cap, that prevents the os- cillator from locking at twice the vertical sync frequency. The oscillator ramp voltage is converted into differential currents superimposed on DC currents of about 315 µA for each out- put. The voltage to current conversion gain is inversely pro- portional to the value of the resistor connected between the Rvert pins (21 and 22). Differential current outputs are pro- vided instead of voltage to avoid ground noise. The ramp voltage goes to the parabolic function generator and to two multipliers used as voltage controlled amplifiers, one for hori- zontal trapezoid correction and the other for horizontal paral- lelogram correction. PARABOLIC FUNCTION GENERATOR The parabolic function generator makes a parabolic wave- form from the vertical ramp. Its output goes to three multipli- ers used as voltage controlled amplifiers, one each for V Dyn Focus, E-W Pin, and H Bow. VOLTAGE CONTROLLED AMPLIFIERS The V Dyn Focus voltage controlled amplifier is controlled by the V Dyn Focus Cntl input. Its output goes to an op amp whose output is V Dyn Focus. The voltage controlled ampli- fier has zero gain at approx. 2V input, maximum positive gain at 4V, and maximum negative gain at 0V. The E-W Pin, H Bow, H Trap and H Para voltage controlled amplifiers are identical to the V Dyn Focus stage, each adjusted by its cor- responding Cntl input. The bandwidth of the Cntl inputs is greater than 125 kHz. The E-W Pin and H Bow amplifiers have the parabolic waveform as their input, and the H Trap and H Para amplifiers have the vertical ramp as their input. The parabolic waveform and the ramp amplitudes track the vertical output amplitude so the correction amplitudes follow accordingly. The outputs of the E-W Pin amplifier (parabola) and the H Trap amplifier (ramp) are summed together in an op amp summing circuit, with H Trap weight 1⁄3 that of E-W Pin. The output of the summing amplifier is H Dyn Width, used for correcting E-W pincushion and horizontal trapezoid distortion. The outputs of the H Bow amplifier (parabola) and the H Para amplifier (ramp) are summed together similarly, with H Bow and H Para equally weighted. The output of the summing amplifier is H Dyn Cntr, used for correcting hori- zontal bow and horizontal parallelogram distortion. All three op amp outputs are identical structures and are typical low output impedance type op amp outputs, capable of sinking or sourcing 5 mA minimum. Block Diagram DS012324-3 FIGURE 3. www.national.com 7 |
同様の部品番号 - LM1295 |
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同様の説明 - LM1295 |
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