Analog Devices,inc.

Vincent James Troy

John Patrick Purcell

Kieran K Heffernan

Martin Gerard Cotter

Joseph Michael Barry

Anthony Gerard Scanlan

A method for converting multi-bit digital video data signals to analogue form wherein the video data signals are in three formats, namely, standard definition, progressive scan and high definition formats, which permits a relatively low order analogue reconstruction filter to be used for filtering the analogue form of the signal. The three formats of the digital video data signals are over-sampled at relatively low over-sampling rates, the standard definition video signals being over-sampled at eight times the nyquist sampling frequency, the progressive scan format signals being over-sampled at four times the nyquist sampling frequency, while the high definition format signals are over-sampled at twice the nyquist sampling frequency. By virtue of the fact that the Video data signals are over-sampled at relatively low over-sampling rates, the over-sampled signals are subjected to sigma-delta modulation in a relatively low order sigma-delta modulator, namely, a second order sigma-delta modulator for noise shaping the quantisation noise. This, thus, permits the analogue reconstruction filter to be provided as a third order filter, and thus of relatively low order.

Method for converting a video signal from one of an analogue and digital form to the other of the analogue and digital form with enhanced signal to noise ratio

A detector circuit ( ) for detecting the presence or absence of a television ( ) on an output ( ) of a video DAC ( ) comprises a comparator ( ) for comparing a voltage developed by the video signal on a control resistor R with a reference voltage of 0.5 volts. The resistor R is of 75 ohms and matches the internal impedance R of 75 ohms of the television ( ). A latch ( ) latches the output from the comparator ( ) onto an output pin Q when the voltage developed across the control resistor R is developed by an equalisation pulse of the vertical blanking interval of the video signal. In the presence of a television ( ) the voltage developed across the control resistor R is 0.35 volts, which pulls the output of the comparator ( ) low, while in the absence of a television ( ) the voltage developed across the control resistor R is 0.7 volts which pulls the output of the comparator ( ) high. A control logic control circuit ( ) reads the output pin Q of the latch ( ) for powering up or powering down the video DAC ( ) as appropriate.

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Raheen, Ireland

Vincent James Troy