Low-band conversion chrominance signal processing apparatus and method therefor

A low-band converting chrominance signal processing apparatus which receives a chrominance signal modulated by a chrominance subcarrier to produce the chrominance signal modulated by a low-band converting chrominance subcarrier or performs the reverse operation, respectively, comprising:

• an automatic frequency control circuit for generating an oscillating signal having a predetermined frequency;
• a chrominance subcarrier generator for receiving said oscillating signal to thereby produce the chrominance subcarrier;
• a low-band converting chrominance subcarrier generator for receiving said oscillating signal to thereby produce the low-band converting chrominance subcarrier;
• a chrominance demodulator for selectively demodulating the chrominance signal modulated by said chrominance subcarrier using said chrominance subcarrier, and demodulating the chrominance signal modulated by said low-band converting chrominance subcarrier using said low-band converting chrominance subcarrier;
• a chrominance processor for processing the chrominance signal demodulated by said chrominance demodulator;
• a chrominance modulator for modulating the chrominance signal processed by said chrominance processor, using said low-band converting chrominance subcarrier or said chrominance subcarrier, respectively;
• a first switch for selecting one of said chrominance subcarrier and said low-band converting chrominance subcarrier and for supplying the selected chrominance subcarrier to said chrominance demodulator;
• and
• a second switch for selecting one of said low-band converting chrominance subcarrier and said chrominance subcarrier to thereby supply the selected chrominance subcarrier to said chrominance modulator,

A method for forming a low-band converting chrominance subcarrier using an oscillating signal having a predetermined frequency, said method comprising the steps of:

• (a) determining a frequency Fscu of the low-band converting chrominance subcarrier and a frequency Fs of the oscillating signal corresponding to the period of one horizontal scanning line, and sampling a basic waveform of the low-band converting chrominance subcarrier at Fs sampling points each having an uniform interval to be stored in one form of a look-up table;
• (b) producing read-addresses for said look-up table to be read Fscu times per Fs oscillating signals;
• and
• (c) generating sampled values corresponding to said read-address from said look-up table,
• whereby Fscu chrominance subcarriers are formed per the Fs oscillating signals.

A method for processing a low-band converted chrominance signal, said method comprising the steps of:

• (a) determining a frequency Fscu of a low-band converting chrominance subcarrier and a frequency Fs of an oscillating signal corresponding to a period of one horizontal scanning line, and sampling a basic waveform of the low-band converting chrominance subcarrier at Fs sampling points each having uniform interval to be stored in a look-up table;
• (b) producing a read-address for said look-up table to be read Fscu times per Fs oscillating signals;
• and
• (c) producing a respective sampled value corresponding to said readaddress from said look-up table,
• whereby Fscu low-band converting chrominance subcarriers are provided per the Fs oscillating signals.

A method for forming a low-band converting chrominance subcarrier using an oscillating signal having a predetermined frequency, said method comprising the steps of:

• (a) determining a frequency Fscu of the low-band converting chrominance subcarrier and a frequency Fs of the oscillating signal corresponding to a period of one horizontal scanning line, and sampling and storing Fscu low-band converting chrominance subcarriers at Fs sampling points each having uniform interval to thereby form a look-up table;
• (b) repetitively counting the oscillating signal per the period of one horizontal scanning line to form a read-address which is supplied to said look-up table;
• and
• (c) producing sampled value corresponding to said read-address from said look-up table,
• whereby Fscu low-band converting chrominance subcarriers are formed per Fs oscillating signals.

A device for forming a low-band converting chrominance subcarrier using an oscillating signal having a predetermined frequency, comprising:

• an output portion for producing values which are sampled from Fscu low-band converting chrominance subcarriers at Fs sampling points each having an uniform interval according to a frequency Fscu of the low-band chrominance converting subcarrier and a frequency Fs of the oscillating signal, wherein the respective frequencies correspond to a period of one horizontal scanning line to thereby generating said low-band converting chrominance subcarrier;
• an address generator for repetitively counting occurrences of the oscillating signal by the period of one horizontal scanning line to thereby form a read-address which is supplied to a look-up table;
• and
• a domain determinator for generating a first domain signal applied to said address generator, wherein said output portion is responsive to said read address.