STV2050A datasheet(48/83 Pages) STMICROELECTRONICS

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STV2050A - CONVERGENCE

9.4 CALIBRATION

Calibrations can be carried out during manufacturing, or during the normal TV operating mode

using the automatic self-alignment procedure via the electrical loop. Refer to Section 11

"ELECTRICAL LOOP" on page 55.

9.5 INTERPOLATION

The 10-bit dynamic correction values are expanded by interpolation to 14 precision bits.

The interpolation of the correction values stored in the embedded RAM produces correction

values for the lines between the grid lines.

9.5.1 Vertical Filter

A vertical interpolation is performed by the STV2050A in order to provide a smooth correction

transition between the stored points. A complex algorithm is implemented in order to improve

the interline geometrical aspect, even when not aligned during chassis production or by the

end user.

9.5.2 Horizontal Filter

For each of the three convergence correction channels, an interpolation filter is implemented

to calculate the correction values between horizontally-adjacent correction values. Different

configuration options are programmable using the D8 register.

The positions of the calculated additional correction values are timed independently for the

visible grid and the retrace grids.

Since operating the filters will increase the DAC frequency by a factor of 2 and 4 respectively,

it may be necessary to switch off the filters during the horizontal retrace if the retrace time is

short and the line frequency is high. In this case, the filter input data, coming from the vertical

interpolation, will be fed directly to the convergence DACs. In any case, this data is processed

by the filters in parallel to avoid any discontinuity when the filters are switched back into the

data paths.

9.6 NORMAL TV OPERATION MODE

The following bits must remain at logical “1” in the E3 register as defined by the default values

during reset:

– the CDO bit (refer to Section 9.8 "CONVERGENCE OUTPUTS" on page 51),

HIF[1:0]

00: Filter is not active

11: Filter is not active

01: Filter is a 3-tap FIR filter (2 values per grid)

10: Filter is a 5-tap FIR filter (4 values per grid)

FSO

0: Filter is switched off during horizontal retrace

1: Filter is running continuously

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