Electronic switch for TV signal booster

1. A method of automatically switching on/off a low noise amplifier (LNA) that serves to boost weak video signals in a TV tuner ( 2 ), the method comprising:

(a) determining ( 23 , 24 , 25 ) whether a tuned-in signal meets predetermined minimum criteria for picture reproduction;

(b) if the determination in step (a) is negative, switching off said LNA ( 33 );

(c) if the determination in step (a) is positive, determining ( 27 , 28 ) whether said tuned-in signal requires boosting;

(d) if the determination in step (c) is negative, switching off said LNA ( 33 );

(e) if the determination in step (c) is positive, switching on said LNA ( 29 );

(f) measuring a change in signal-to-noise ratio of the LNA-amplified tuned-in signal after switching on said LNA in step (e), and

(g) if said measured change in step (f) is an increase and exceeds a predetermined threshold ( 31 ), maintaining said LNA in a switched-on state, and otherwise switching off said LNA ( 33 ).

2. A method according to claim 1 , wherein step (c) comprises determining ( 27 ) whether an AGC feedback voltage to said TV tuner ( 2 ) exceeds a first threshold.

3. A method according to claim 1 , wherein step (c) comprises determining ( 28 ) whether a signal-to-noise level of said tuned-in signal is below a second threshold.

4. A method according to claim 1 , wherein step (c) comprises determining ( 27 ) whether an AGC feedback voltage to said TV tuner ( 2 ) exceeds a first threshold and, if so, whether ( 28 ) a signal-to-noise level of said tuned-in signal is below a second threshold.

5. A method according to claim 1 , further comprising:

(h) delaying ( 30 , 301 , 302 ) a release of picture blanking ( 32 ), pending the completion of step (g).

6. An electronic control for automatically switching on/off a low noise amplifier (LNA) that serves to boost weak video signals in a TV tuner ( 2 ), comprising:

input means ( 13 , 14 , 15 , 16 , 17 ) for receiving first and second input data;

processing means ( 7 ) receiving said data from the input means ( 13 , 14 , 15 , 16 , 17 );

output means ( 12 ) for outputting a control signal to enable or disable said LNA;

wherein the processing means:

(a) determines from said first data whether a tuned-in signal meets predetermined minimum criteria for picture reproduction;

(b) switches off said LNA, if the determination in step (a) is negative;

(c) determines from said second data ( 16 , 17 ) whether said tuned-in signal requires boosting, if the determination in step (a) is positive;

(d) switches off said LNA, if the determination in step (c) is negative;

(e) switches on said LNA, if the determination in step (c) is positive;

(f) measures a change exhibited by said second data ( 16 ) in signal-to-noise ratio of the LNA-amplified tuned-in signal after switching on said LNA in step (e), and

(g) if said measured change in step (f) is an increase and exceeds a predetermined threshold, generating said control signal at said output means ( 12 ) to maintain said LNA in a switched-on state, and otherwise generating said control signal at said output means ( 12 ) to switch off said LNA.

7. An electronic control according to claim 6 , wherein the second input data ( 16 , 17 ) comprises data representing AGC feedback voltage to said TV tuner ( 2 ) and step (c) comprises determining whether the second input data ( 17 ) exceeds a first threshold.

8. An electronic control according to claim 6 , wherein the second input data ( 16 ) comprises data representing a signal-to-noise level of said tuned-in signal and step (c) comprises determining whether the second input data is below a second threshold.

9. An electronic control according to claim 6 , wherein the second input data ( 16 , 17 ) comprises data representing AGC feedback voltage to said TV tuner and data representing a signal-to-noise level of said tuned-in signal, and step (c) comprises determining whether said AGC feedback voltage exceeds a first threshold and, if so, whether said signal-to-noise level of said tuned-in signal is below a second threshold.

10. An electronic control as claimed in claim 6 wherein the first input data ( 13 ) represents the presence of video sync pulses.

11. An electronic control as claimed in claim 6 wherein the first input data ( 14 ) represents the detection of chrominance signal.

12. A TV comprising a TV tuner with an electronic control for automatically switching on/off a low noise amplifier (LNA) that serves to boost weak signals in said TV tuner ( 2 ) as claimed in claim 6 .