PT4 Multi-standard Video Decoder

The decoder accepts 10-bit composite line locked video sampled at 27MHz together with synchronising signals and clock, (for example from the Analog Devices AD9981 ADC). The decoder is a complementary design.

The colour burst from the input video is used to phase lock the subcarrier oscillator which then addresses a sine and cosine LUT. These waveforms are used to demodulate the colour component of the composite waveform. The resulting U and V colour components are then low pass filtered and applied to a 3 line comb, 263/312 line field comb and 525/625 line frame comb filter.

The chrominance comb adapts between all the available comb modes on a pixel by pixel basis based on the chrominance and luminance amplitude differences across the comb aperture. The resulting combed U and V components provide the colour component outputs where they are amplified and scaled before being formatted to a 10-bit BT656 output. The combed U and V are also remodulated onto the colour subcarrier and subtracted from the composite to produced a combed luminance output which is also scaled and formatted into the BT656 stream.

Control and status registers are written to and read from using a conventional 8 bit wide microprocessor interface.