RF receiving apparatus
View Patent ↗A level comparator supplied with oscillation signal of local oscillator for comparing the signal level of oscillation signal with a certain predetermined threshold value, and a driving section interposed between the output of level comparator and a control section are provided. When the level comparator recognized that the signal level exceeded the threshold value, it puts the driving section into operation for bringing the control section into action.
1. A RF receiving apparatus comprising
an input terminal;
a direct conversion system mixing circuit supplied at one input with RF signal inputted to the input terminal while at another input with an oscillation signal of local oscillator, for outputting a plurality of output signals whose phases are different to each other;
a suppression part supplied with the output of the mixing circuit;
an output terminal supplied with the output of suppression part;
a detector for detecting DC offset voltage contained in the output signals of the mixing circuit;
a control section interposed between the output of the detector and the input of the suppression part, wherein the control section outputting a signal to the suppression part for suppressing the DC offset voltage when the detector detected the DC offset voltage;
a level comparator supplied with the oscillation signal for comparing an oscillation signal level with a certain predetermined threshold value; and
a driving section interposed between the output of level comparator and the control section, when the level comparator detects that the signal level exceeded the threshold value, the level comparator signals the driving section to trigger the control section to control the suppression part to suppress the DC offset voltage.
2. The RF receiving apparatus of claim 1 , wherein
the level comparator is connected with a memory for storing the upper limit value of threshold value, if the level comparator recognized that the signal level of oscillation signal had a value greater than the upper limit value it registers a value that is the upper limit value plus a certain predetermined value in the memory as new upper limit value.
3. The RF receiving apparatus of claim 2 , wherein
the memory stores the bottom limit value of threshold value, if the level comparator recognized that the signal level of oscillation signal had a value that is greater than the upper limit value it registers the upper limit value in the memory as new bottom limit value.
4. The RF receiving apparatus of claim 1 , wherein
the level comparator is connected with a memory for storing the bottom limit value of threshold value, if the level comparator recognized that the signal level of oscillation signal had a value smaller than the bottom limit value it registers a value that is the bottom limit value minus a certain predetermined value in the memory as new bottom limit value.
5. The RF receiving apparatus of claim 4 , wherein
the memory stores the upper limit value of threshold value, if the level comparator recognized that the signal level of oscillation signal had a value smaller than the bottom limit value it registers the bottom limit value in the memory as new upper limit value.
6. The RF receiving apparatus of claim 1 , wherein
the memory connected with the level comparator stores beforehand a threshold value and a signal level reference value, if the level comparator recognized that a difference between an inputted signal level and the signal level reference value exceeded the threshold value it makes the control section to operate the driving section.
7. The RF receiving apparatus of claim 6 , wherein
if the level comparator recognized that a difference between the inputted signal level and the signal level reference value exceeded the threshold value it registers the value of inputted signal level in the memory as new signal level reference value.
8. The RF receiving apparatus of claim 1 , wherein
the control section generates a cancellation signal of negative voltage for canceling the DC offset voltage, and
the suppression part is consisting of a composer for composing the cancellation signal and the output of mixing circuit together.
9. A RF receiving apparatus comprising
an input terminal;
a first mixing circuit of direct conversion system supplied at one input with RF signal inputted to the input terminal while at another input with an oscillation signal of local oscillator;
a second mixing circuit supplied at the one input with the output of first mixing circuit while at the another input with an output of fixed oscillator;
a composer for composing a plurality of signals outputted from the second mixing circuit together;
an output terminal supplied with the output of composer;
a suppression part provided between the first mixing circuit and the second mixing circuit, or between the second mixing circuit and the composer;
a detector for detecting DC offset voltage contained in the output signal of first mixing circuit;
a control section interposed between the output of the detector and the input of the suppression part, wherein; the control section outputting a signal to the suppression part for suppressing the DC offset voltage when the detector detected the DC offset voltage;
a level comparator supplied with an oscillation signal outputted from either the local oscillator or the fixed oscillator for comparing signal level of the oscillation signal with a certain predetermined threshold value; and
a driving section interposed between the output of level comparator and the control section are provided, when the level comparator recognized that the signal level exceeded the threshold value, the level comparator signals the driving section to trigger the control section to control the suppression part to suppress the DC offset voltage.
10. The RF receiving apparatus of claim 9 , wherein
the control section generates cancellation signal having a phase that is different from converted DC offset signal by 180 degrees for canceling the converted DC offset signal which has been converted by the second mixer into intermediate frequency signal,
the composer is supplied with the cancellation signal generated at the control section, and
the suppression part is the composer which composes the cancellation signal and the output of second mixing circuit together.
11. The RF receiving apparatus of claim 9 , wherein
the level comparator makes judgment on the signal level of fixed oscillator's oscillation signal.
12. The RF receiving apparatus of claim 9 , wherein
the level comparator is connected with a memory for storing the upper limit value of threshold value, if the level comparator recognized that the signal level of oscillation signal had a value greater than the upper limit value it registers a value that is the upper limit value plus a certain predetermined value in the memory as new upper limit value.
13. The RF receiving apparatus of claim 12 , wherein
the memory stores the bottom limit value of threshold value, if the level comparator recognized that the signal level of oscillation signal had a value that is greater than the upper limit value it registers the upper limit value in the memory as new bottom limit value.
14. The RF receiving apparatus of claim 9 , wherein
the level comparator is connected with a memory for storing the bottom limit value of threshold value, if the level comparator recognized that the signal level of oscillation signal had a value smaller than the bottom limit value it registers a value that is the bottom limit value minus a certain predetermined value in the memory as new bottom limit value.
15. The RF receiving apparatus of claim 14 , wherein
the memory stores the upper limit value of threshold value, if the level comparator recognized that the signal level of oscillation signal had a value smaller than the bottom limit value it registers the bottom limit value in the memory as new upper limit value.
16. The RF receiving apparatus of claim 9 , wherein
the memory connected with the level comparator stores beforehand a threshold value and a signal level reference value, if the level comparator recognized that a difference between an inputted signal level and the signal level reference value exceeded the threshold value it makes the control section to operate the driving section.
17. The RF receiving apparatus of claim 16 , wherein
if the level comparator recognized that a difference between the inputted signal level and the signal level reference value exceeded the threshold value it registers the value of inputted signal level in the memory as new signal level reference value.