- Automatic Picture Tube Bias Cutoff Control
- Automatic Background Color Balance
- Eliminates Grey Scale Adjustments
- Compensates for Cathode-to-Heater Leakage
- Electrostatic Protection on All Pins
- Servo Loop Design
- Wide Dynamic Range
- Three-Gun Control
- Minimal External Components
The CA3224E is an automatic picture tube bias control circuit used in color TV receiver CRT drive circuits. It is used to provide dynamic bias control of the grey scale both initially and over the CRT operating life, compensating for CRT cutoff changes.
The CA3224E provides automatic continuous control of the cutoff current in each gun of a three-gun color CRT. From an input pulse amplitude proportional to the difference between the desired and the actual CRT cutoff, a gated sample/hold circuit generates a DC correction voltage which correctly biases the CRT driver circuit. The sample/hold bias correction takes place each frame following the vertical blanking. Figure 1 shows a block diagram of the CA3224E. The functions include three identical servo loop transconductance amplifiers with a sample/hold switch and buffer amplifier plus control logic, internal bias and a mode.