DAEWOO 2896ST
Manual de Servicio

No 43

Name PHI-1 FILTER

Description The loopfilter connected to pin 43 is suitable for various signal conditions as strong/weak and VCR signal. This is achieved by switching of the loopfilter time constant by changing the PHI-1 output current. Via I2C bus FOA/B, different time constants can be chosen, including an automatic mode which gives optimal performance under varying conditions. To this pin are connected the IC-substrate and horizontal output. The EW drive is a current output. The output is single-ended and is fed directly to the EW-input terminal The vertical drive has a current output. The output is balanced which ensures a good common mode behavior with temperature and makes the output signal less sensitive for disturbances. The PLL frequency range is 32-60MHz with corresponding VCO frequency 64-120MHz. The IF input impedances is 2 in parallel with 3pF and matches the required load for commonly used SAW filters. A DC coupling is allowed, so no series capacitors between SAW filter and IF input are necessary. The input range for EHT tracking is 1.2 ~ 2.8V, for a compensation of +/- 5% on vertical and/or EW. The tracking on EW can be switched on/off by HCO. The overvoltage protection is activated when the voltage on pin 50 exceeds 3.9V typical. This pin requires a capacitor to ground of l00nF +/- 5%. The optimal sawtooth amplitude is 3.5V and is determined by the external capacitor and charge current. The sawtooth bottom-level is 2V. This pin requires a resistor to ground. The optimal reference current is 100 . which is determined by this resistor. The AGC capacitor value is 2.2 and has been defined for an optimal compromise between AGC speed and tilt for all AGC modes (negative/positive modulation). This output is used to control (reduce) the tuner gain for strong RF signals. The tuner AGC is an open collector output which is acting as a variable current source to ground. not used. This pin requires a capacitor of 10 connected to ground. The pin acts as a low pass filter needed for the DC feedback loop.

44 45 46 47 48 49

GROUND EAST-WEST DRIVE VERT DRIVE + VERT DRIVE IF INPUT

50

EHT/OVERVOLTAGE PROTECT INPUT

51

VERT SAWTOOTH CAPACITOR REFERENCE CURRENT INPUT AGC DECOUPLING CAPACITOR

52 53

54

TUNER AGC OUTPUT AUDIO DEEMPHASSIS DECOUPLING SOUND DEMODULATOR

55 56

20