Method for determining the signal strength at the input of a tuner
View Patent ↗The invention relates to a method for determining the strength of a signal ( 18 ) at the input of a tuner ( 1 a .) In this, the frequency-dependent amplification characteristic for the tuner is measured and stored in a memory assigned to the tuner. With the help of this characteristic the frequency-dependent variation of the amplification can be compensated during tuner operation, in order that the input signal strength can be deduced more precisely. For a tuner with automatic gain control (AGC), the frequency dependence of the AGC can also be recorded and stored in the memory by representative characteristics. The consideration of the AGC characteristics results in a further improvement to the precision of estimation of the input signal strength.
1. A method for determining the signal strength at an input of a tuner, an amplification characteristic of an amplification section for receiving and amplifying an input signal and outputting an output signal of the tuner being measured and stored depending on the input signal frequency, and the stored characteristic then being used during the operation of the tuner to calculate the signal strength at the tuner's input from the tuner's output signal;
adjusting a gain of the amplification section by a tuner automatic gain control (AGC) circuit adapted to receive a tuner AGC feedback voltage,
storing data corresponding to two or more tuner AGC reference gain curves measured at two or more corresponding input frequencies; and
storing each tuner AGC reference gain curve in a corresponding plurality of selected memory locations, each of the selected memory locations corresponding to an tuner AGC gain reduction level and storing therein a measured tuner AGC feedback voltage when the tuner AGC circuit has the corresponding tuner AGC gain reduction and when the input signal has the corresponding input frequency.
2. A method as claimed in claim 1 , wherein the amplification of the tuner is reduced by means of at least one control signal, in order to obtain a predefined strength for the tuner's output signal.
3. A method as claimed in claim 1 , further comprising:
storing the measured frequency tilt data in memory; and using the stored frequency tilt data during turner operation.
4. A tuner, comprising:
an amplification section adapted to receive and amplify an input signal and to output an output signal;
a memory device including a plurality of memory locations, each of the memory locations corresponding to a different input frequency and storing therein a measured gain of the amplification section when the input signal has the corresponding input frequency; and
a signal processing unit adapted to calculate a strength of the input signal at an actual input frequency using a strength of the output signal and the measured gain of the amplification section stored in the memory location corresponding to the actual input frequency of the input signal;
wherein the amplification section further comprises a tuner automatic gain control (AGC) circuit adapted to receive a tuner AGC feedback voltage and in response thereto to adjust the gain of the amplification section, wherein the memory device further stores data corresponding to two or more tuner AGC reference gain curves measured at two or more corresponding input frequencies; and
wherein the memory device stores each tuner AGC reference gain curve in a corresponding plurality of selected memory locations, each of the selected memory locations corresponding to an tuner AGC gain reduction level and storing therein a measured tuner AGC feedback voltage when the tuner AGC circuit has the corresponding tuner AGC gain reduction and when the input signal has the corresponding input frequency.
5. The tuner of claim 4 , wherein each of the selected memory locations corresponds to a different input power level in steps of 1 db.
6. The tuner of claim 4 , wherein each of the memory locations corresponding to a different input frequency further stores an identifier of one of the two or more tuner AGC reference curves which applies to the corresponding input frequency, and wherein the signal processing unit calculates the strength of the input signal at the actual input frequency using the AGC reference curve identified in the memory location corresponding to the actual input frequency.
7. The tuner of claim 6 , wherein each of the memory locations corresponding to a different input frequency further stores data corresponding to a different input frequency further stores data corresponding to a frequency slope of the tuner at the corresponding input frequency.
8. The tuner of claim 4 , wherein the amplification section further comprises an intermediate frequency (IF) automatic gain control (AGC) circuit adapted to receive an IF AGC feedback voltage and in response thereto to adjust the gain of the amplification section, wherein the memory device further stores data corresponding to an IF AGC reference gain curve.
9. The tuner of claim 4 , wherein the amplification section includes at least two frequency converters.
10. The tuner of claim 4 , wherein the memory device stores the amplification characteristic as a plurality of gain values each corresponding to a different frequency of the tuner, wherein each data value corresponds to the gain of the amplifier in dB at the corresponding frequency.