COLOR TELEVISION SIGNAL DEMODULATION SYSTEM

• US 3,558,810 A
• Filed: 02/10/1969
• Issued: 01/26/1971
• Est. Priority Date: 02/10/1969
• Status: Expired due to Term

• Current Assignee: Cecchin Gildo, Francis H. Hilbert
• Original Assignee: Cecchin Gildo, Francis H. Hilbert
• Inventors: CECCHIN GILDO, Hilbert, Francis H.
• Application Number:
  US04/797,973
• Time in Patent Office: 715 Days
• US Class Current: 348/641
• CPC Class Codes: H04N 9/66 for synchronous demodulators

Abstract

A silicon monolithic integrated circuit consisting of three sets of full-wave, synchronous, switched demodulators is used to demodulate the red, blue and green color signals present in a composite television signal. Each of the demodulators consists of two pairs of switching transistors with the transistors in each of the pairs being rendered alternately conductive by a reference signal derived from the reference oscillator in a color television receiver. The phase of the red and the blue reference oscillator signals are obtained in a conventional manner, and the phase for the green reference signal is obtained by adding a predetermined portion of the red and blue signals together in a resistive adder to provide the green oscillator signal. The color signals are supplied in alternate phase to the two pairs of switching transistors in each of the demodulators, and the brightness signal components are applied equally or push-push to the switching transistors of the demodulators through an input transistor for each of the demodulators. In order to provide the proper relative amounts of gain for three demodulators, the red and blue signal demodulators have shunting resistance circuits connected across the input transistor circuits; and the green demodulator has a shunt connected across equal taps on voltage dividers connected to the outputs thereof. Since the brightness signal components are balanced with respect the the shut devices, the brightness signal passes through all of the demodulators unaffected by the shunting circuits.

Claims

1. A color television receiver for a signal comprising brightness signal components of a television image and a subcarrier signal modulated by color difference signals representing hue and saturation of the image at different phases of the subcarrier, and having a reference oscillator providing reference signals at the subcarrier frequency and at different phases, said receiver including in combination:

a plurality of full wave demodulators, each including two pairs of switching devices, with each of the switching devices from one pair in each demodulator coupled in a common output with a different one of the switching devices from the other pair in the same demodulator;

meAns for supplying said reference signals at the subcarrier frequency and at different phases to the demodulators, with the common-connected switching devices of each demodulator being alternately rendered conductive at the subcarrier frequency for providing normal and inverted output signals representing a different color from each of the demodulator devices;

first means applying the brightness signal and the modulated subcarrier signal of one phase to one of the pairs of switching devices in each demodulator; and

second means applying the brightness signal and the modulated subcarrier signal of opposite phase to the other of the pairs of switching devices in each of the demodulators.

2. The combination according to claim 1 wherein each of the demodulators includes two paths carrying the subcarrier signal, each of the paths including different ones of the applying means, switching devices and outputs from the switching devices, with the two paths in each of the demodulators carrying subcarrier signals of opposite phases, and further including means for cross-coupling the paths to attenuate the out-of-phase subcarrier signals.

3. The combination of claim 2 wherein the cross-coupling means includes an impedance for attenuating the demodulated subcarrier signal.

4. The combination of claim 1 further including a shunt impedance connected between the first and second signal applying means of at least one of the demodulators to form a subcarrier signal divider therewith for altering the gain of demodulated subcarrier signal appearing at the outputs of the switching devices of that demodulator with respect to the level of the brightness signal components;

and shunting means connected between the outputs of at least one of the demodulators for adjusting the amplitude of the demodulated subcarrier signal appearing at the outputs of the demodulator having the shunt connected across the outputs while allowing the brightness signal components to be developed at those outputs in an unadjusted form.

5. The combination according to claim 4 wherein the shunt impedance and the shunting means are connected to different demodulators.

6. The combination of claim 1 wherein the switching devices are integrated circuit transistors of the same conductivity type.

7. A color demodulator for demodulating a television signal comprising brightness signal components of a television image and a subcarrier signal modulated by color difference signals representing hue and saturation of the image at different phases of the subcarrier, the ratio of subcarrier signal with respect to brightness signal components being different for image portions of different hue, said demodulator including in combination:

two switching means, each including first and second switching devices, with the outputs of the first device of each switching means and the second device of the other switching means being connected together to form two outputs, respectively, with the first and second switching devices in each switching means being adapted for alternate switching in response to a reference signal, the first device being nonconductive when the second device is conductive and vice versa;

means for applying a reference signal at the subcarrier frequency to the switching devices;

a first signal supply circuit for providing the subcarrier signal at one phase and the brightness signal components to one of the switching means;

a second signal supply circuit providing the subcarrier signal at opposite phase and the brightness signal components to the second switching means; and

shunting means connected across the outputs for altering the gain of the subcarrier signals while permitting the brightness signal components to be passed to the outputs of the switching means unaltered in gain.

8. The combination of claim 7 wherein the shunting means is a resistance means.

9. The combination according to claim 7 further including a second demodulator having first and second switching means each including first and second switching devices with the outputs of the first switching device of each switching means and the second device of the other switching means being connected together to form two outputs, with the reference signal, the subcarrier signal, and the brightness signal components being supplied to the second demodulator circuit in the same manner as they are supplied to the first demodulator circuit and wherein a shunt impedance is connected between the first and second inputs to the second demodulator from the first and second supply circuits to form a subcarrier signal divider to adjust the gain of the second demodulator for the subcarrier signal with respect to the level of the brightness signal components.

10. The combination of claim 9 wherein the first and second signal applying means are input transistors, with a different input transistor supplying the signals to each pair of switching devices.

11. The combination according to claim 7 wherein the first and second switching devices in each of the switching means include transistors driven between conduction and cutoff by the reference signal means.

12. In a color television receiver for a signal comprising brightness signal components of a television image and a subcarrier signal modulated by color difference signals representing hue and saturation of the image at different phases of the subcarrier, a plurality of demodulating circuits for demodulating each of the different phases of the subcarrier signal including in combination:

means for supplying signals at the subcarrier frequency to the inputs of at least two of the demodulators, said supplied signals being of different phases to provide output signals representing different colors from each of the demodulators; and

an adder circuit connected between the inputs to said two demodulators to provide at the output thereof a signal at the subcarrier frequency from the signal supplying means, with said signal being supplied to a third demodulator for operating that demodulator at the subcarrier frequency to provide a signal representing a third color.

13. The combination of claim 12 wherein the supplied signal is a reference signal which is supplied to the first and second demodulators at first and second phases thereof;

and wherein a predetermined amplitude of the first and second phases of the reference signal is combined in the adder circuit to provide the reference signal supplied to a third of said demodulators; and

further wherein each of said demodulators is a full wave synchronous demodulator with the output of said third demodulator being obtained 180* out of phase with the outputs obtained from the first and second demodulators.

14. The combination according to claim 13 wherein the first and second demodulators are red and blue signal demodulators, respectively, and wherein the third demodulator is the green signal demodulator.

15. The combination of claim 14 wherein different percentages of the red and blue reference signals are combined to form the green reference signals.

16. A color demodulator for demodulating a television signal comprising brightness signal components of a television image and a subcarrier signal modulated by color difference signals representing hue and saturation of the image at different phases of the subcarrier, the ratio of the subcarrier signal with respect to brightness signal components being different for image portions of different hue, said demodulator including in combination:

two switching means, each including first and second switching devices, with the outputs of the first device of one switching means and the second device of the other switching means being connected together to form two outputs respectively, the first and second switching devices in each switching means being adapted for alternate switching in response to a reference signal, and the first device being nonconductive when the second device is conductive and vice versa meaNs for applying a reference signal at the subcarrier frequency to the switching devices;

a first signal supply circuit for providing the subcarrier signal at one phase to one of the switching means;

a second signal supply circuit providing the subcarrier signal at opposite phase to the second of the switching means;

said first signal supply circuit and the switching devices interconnecting that signal supply circuit with one of the outputs at any instant providing a first signal path, and the second signal supply circuit and the switching devices interconnecting that supply circuit with the other of the outputs at any instant providing a second signal path; and

shunting means connected across the first and second signal paths for attenuating the outputs of the switching devices with respect to the subcarrier signals.

17. Apparatus according to claim 16 wherein the shunting means is connected across the outputs.

18. Apparatus of the type according to claim 16 further including a plurality of demodulators wherein the shunting means of at least one of the demodulators is connected across the outputs and wherein the shunting means of at least one of the other demodulators is connected across the first and second signal supply circuits.