For more thorough understanding of the present invention and advantages thereof, the following description should be read in conjunction with the accompanying drawings, in which:
At least the following details will become apparent from descriptions of this specification and of the accompanying drawings.
==Overall Configuration==
The high-frequency tuning circuit 11 performs tuning operation to extract a reception signal having a desired reception frequency fr from FM reception signals input to the antenna 10. The high-frequency tuning circuit 11 controls a tuning frequency to be fr based on a control signal input from the microcomputer 27. The high-frequency amplification circuit 12 amplifies and outputs the signal having the reception frequency output from the high-frequency tuning circuit 11.
The local oscillation circuit 13 outputs a local oscillation signal having a frequency higher than the reception frequency fr by a predetermined intermediate frequency fi (e.g., 10.7 MHz). The local oscillation circuit 13 controls the frequency of the local oscillation signal to be fr+fi based on the control signal input from the microcomputer 27.
The mixing circuit 14 mixes the reception signal having the frequency fr output from the high-frequency amplification circuit 12 and the local oscillation signal having the frequency fr+fi output from the local oscillation circuit 13 to output a signal corresponding to a difference component. The intermediate frequency amplification circuit 15 amplifies the signal output from the mixing circuit 14 and allows passage of only a frequency component near the predetermined intermediate frequency fi to generate an intermediate frequency signal.
The detection circuit 16 performs a detection process for the intermediate frequency signal output from the intermediate frequency amplification circuit 15 to convert the signal into a stereo composite signal. The stereo composite signal is synthesized from an L-signal (left audio signal) component, an R-signal (right audio signal) component, and, for example, a 19-kHz pilot signal.
The pilot detection circuit 17 detects the frequency of the pilot signal included in the stereo composite signal output from the detection circuit 16. The frequency of the pilot signal is detected by the pilot detection circuit 17 and input to the microcomputer 27.
The oscillation circuit 18 outputs a signal having a frequency (e.g., 456 kHz obtained by multiplying 19 kHz by 24) corresponding to the frequency (e.g., 19 kHz) of the pilot signal. The oscillation circuit 18 performs control to generate the oscillation frequency corresponding to the frequency of the pilot signal based on the control signal input from the microcomputer 27.
From the signal output from the oscillation circuit 18 and having the frequency (e.g., 456 kHz) corresponding to the frequency of the pilot signal, the stereo demodulation circuit 19 generates a subcarrier signal having a frequency (e.g., 38 kHz) obtained by doubling the frequency of the pilot signal, for example. The stereo demodulation circuit 19 loads the stereo composite signal output from the detection circuit 16 in synchronization with the subcarrier signal to pick up and output the L-signal and the R-signal from the stereo composite signal.
The low-frequency amplification circuit 20L amplifies the L-signal output from the stereo demodulation circuit 19 and outputs the L-signal to the speaker 21L. The low-frequency amplification circuit 20R amplifies the R-signal output from the stereo demodulation circuit 19 and outputs the R-signal to the speaker 21R.
Under the control of the microcomputer 27, the switch circuit 24 selects a signal output from any one of the high-frequency tuning circuit 11, the local oscillation circuit 13, and the oscillation circuit 18 and outputs the signal to the counter 25. The counter 25 counts and outputs a number of times of oscillation of an input signal within a predetermined time.
The operating unit 26 is used by a user for selecting a desired reception frequency and is, for example, a dial-type or button-type frequency input apparatus.
The microcomputer 27 outputs a control signal for controlling the oscillation frequencies of the high-frequency tuning circuit 11, the local oscillation circuit 13, and the oscillation circuit 18. When controlling the oscillation frequency of the high-frequency tuning circuit 11, the microcomputer 27 switches the switch circuit 24 toward the high-frequency tuning circuit 11 and acquires the output of the counter 25. The microcomputer 27 changes and outputs the control signal to the high-frequency tuning circuit 11 such that the counted number output from the counter 25 becomes a counted number indicating the reception frequency selected by the operating unit 26. When controlling the oscillation frequency of the local oscillation circuit 13, the microcomputer 27 switches the switch circuit 24 toward the local oscillation circuit 13 and acquires the output of the counter 25. The microcomputer 27 changes and outputs the control signal to the local oscillation circuit 13 such that the counted number output from the counter 25 becomes a counted number indicating a frequency obtained by adding the intermediate frequency to the reception frequency selected by the operating unit 26. When controlling the oscillation frequency of the oscillation circuit 18, the microcomputer 27 switches the switch circuit 24 toward the oscillation circuit 18 and acquires the output of the counter 25. The microcomputer 27 changes and outputs the control signal to the oscillation circuit 18 such that the counted number output from the counter 25 becomes a counted number indicating a frequency (e.g., 456 kHz) corresponding to the frequency of the pilot signal.
==Detailed Configuration==
Detailed configurations of the high-frequency tuning circuit 11, the local oscillation circuit 13, and the oscillation circuit 18 will be described.
The registers 53, 54 are, for example, eight-bit storage circuits and store the control signal output from the microcomputer 27. In this embodiment, the control signal is eight bits.
The switch circuits S1 to S8 are turned on/off in accordance with a value of each bit of the control signal output from the register 53. In this embodiment, each one of the switch circuits S1 to S8 is turned on if corresponding bit of the control signal is “0” and is turned off if corresponding bit of the control signal is “1”.
Therefore, for example, if the control signal is 0×00 (0× indicates hexadecimal expression), all the switch circuits S1 to S8 are turned on; if the control signal is 0×01, only the switch circuit S8 is turned off and the switch circuits S1 to S7 are turned on; and if the control signal is 0×FF, all the switch circuits S1 to S8 are turned off.
In the high-frequency tuning circuit 11, when all the switch circuits S1 to S8 are turned on, the composite capacitance of the capacitors C1 to C8 is maximized and the tuning frequency is minimized. When all the switch circuits S1 to S8 are turned off, the composite capacitance of the capacitors C1 to C8 is minimized and the tuning frequency is maximized. The variable range of the tuning frequency due to turning on/off of the switch circuits S1 to S8 can be on the order of 75 MHz to 110 MHz, for example.
The DAC 55 changes the control signal output from the register 54 into a reverse bias voltage, which is output and applied to the varicaps 51, 52. If the voltage output from the DAC 55 is decreased, the capacitances of the varicaps 51, 52 are increased and the tuning frequency is decreased. On the other hand, if the voltage output from the DAC 55 is increased, the capacitances of the varicaps 51, 52 are decreased and the tuning frequency is increased.
In an embodiment, the voltage output from the DAC 55 changes in proportion to the control signal output from the register 54. Therefore, the tuning frequency is decreased as the value of the control signal is decreased, and the tuning frequency is increased as the value of the control signal is increased. The variable width of the tuning frequency due to the changes in capacitances of the varicaps 51, 52 can be on the order of 1 MHz.
In this high-frequency tuning circuit 11, under the control of the microcomputer 27, the control signal set in the register 53 is adjusted to drive the tuning frequency to the vicinity of the desired reception frequency. Under the control of the microcomputer 27, the control signal set in the register 54 is then adjusted to set the tuning frequency to the reception frequency. For example, if the desired reception frequency is 80.0 MHz, the tuning frequency is adjusted on the order of 79.5 MHz to 80.5 MHz by the control signal set in the register 53 and the tuning frequency is finely adjusted to become 80.0 MHz by the control signal set in the register 54.
The register 64 is, for example, eight-bit storage circuits and stores the control signal output from the microcomputer 27.
The DAC 65 changes the control signal output from the register 64 into a reverse bias voltage, which is output and applied to the varicaps 62, 63. If the voltage output from the DAC 65 is decreased, the capacitances of the varicaps 62, 63 are increased and the oscillation frequency is decreased. On the other hand, if the voltage output from the DAC 65 is increased, the capacitances of the varicaps 62, 63 are decreased and the oscillation frequency is increased.
In an embodiment, the voltage output from the DAC 65 changes in proportion to the control signal output from the register 64. Therefore, the oscillation frequency is decreased as the value of the control signal is decreased, and the oscillation frequency is increased as the value of the control signal is increased.
The local oscillation circuit 13 and the oscillation circuit 18 can also be configured such that the capacitances of the capacitors 61, 71 are changed in accordance with the control signal as is the case with the high-frequency tuning circuit 11.
The frequency acquiring unit 90 outputs the control signals having a plurality of values to acquire the oscillation frequency of the high-frequency tuning circuit 11, the local oscillation circuit 13, or the oscillation circuit 18 at each value.
The frequency characteristic calculating unit 93 calculates data indicating a relationship between the oscillation frequencies and the values of the control signals in the high-frequency tuning circuit 11, the local oscillation circuit 13, or the oscillation circuit 18 with a least-square method, based on the plurality of values of the control signals output from the frequency acquiring unit 90 and a plurality of the oscillation frequencies acquired by the frequency acquiring unit 90.
The control signal output unit 95 outputs the control signal setting the oscillation frequency to the target frequency to the high-frequency tuning circuit 11, the local oscillation circuit 13, or the oscillation circuit 18, based on the data calculated by the frequency characteristic calculating unit 93
==Description of Operation==
Operation of adjusting the oscillation frequency in the FM radio receiver 1 will be described. First, an outline of a process of determining the control signal will be described with an example when an approximate curve showing the frequency characteristic of the oscillation frequency in the high-frequency tuning circuit 11 is a quadratic curve.
As shown in
An error Sn of (xn, yn) is Sn=(yn−c0−c1xn−c2xn2)2. Since partial differentiation is zero at the minimum points of c0, c1, and c2, dS/dc0=0, dS/dc1=0, and dS/dc2=0 are established. Therefore, the following equations (2) to (4) are satisfied.
The following equations (5) to (7) are derived from the equations (2) to (4).
The equations (5) to (7) can be represented by the following equation (8) with a matrix.
That is, the frequency characteristic calculating unit 93 can calculate the coefficients c0, c1, and c2 based on the equation (8).
When the coefficients c0, c1, and c2 are calculated by the frequency characteristic calculating unit 93, the control signal output unit 95 substitutes a desired reception frequency (target frequency) into f(x) to obtain the control signal corresponding to the reception frequency. The control signal output unit 95 outputs the obtained control signal to the register 53 of the high-frequency tuning circuit 11. The same procedure can be used to obtain the control signals output to the register 54 of the high-frequency tuning circuit 11, the register 64 of the local oscillation circuit 13, and the register 74 of the oscillation circuit 18.
Although description has been made of an example when the order of the approximate curve of the frequency characteristic is the second order, if the order of the approximate curve is the mth order, the equation (8) can be represented by (Ai,j)(ci)=(Bi) <i=0, 1, . . . m; j=0, 1, . . . m>. Ai,j and Bi are represented by the following equations (9) and (10).
From (Ai,j)(ci)=(Bi), ci can be obtained and substituted into f(x) to determine the value of the control signal corresponding to the target frequency.
Details of the control signal determining process will be described with reference to a flowchart.
When the reception frequency is input from the operating unit 26, the frequency acquiring unit 90 outputs N control signals yn (n=0, 1, . . . N-1) to the register 53 of the high-frequency tuning circuit 11 and acquires tuning frequencies xn corresponding to the control signals yn based on a counted number output from the counter 25 (S701).
The frequency characteristic calculating unit 93 obtains the coefficients c0 to cm (first data) of the mth approximate curve representing the frequency characteristic of the high-frequency tuning circuit 11 with the above least-square method (S702) and store the coefficients c0 to cm into a writable memory such as RAM (Random Access Memory) included in the microcomputer 27 (S703).
The control signal output unit 95 substitutes the reception frequency (target frequency) into f(x) determined by the coefficients c0 to cm stored in the memory to calculate the value of the control signal corresponding to the reception frequency (S704) and outputs the calculated value of the control signal to the register 53 of the high-frequency tuning circuit 11 (S705).
The coefficients c0 to cm (first data) are also calculated for the register 54 of the high-frequency tuning circuit 11 by the above process (S701 and S702), and the control signal corresponding to the target frequency is output based on the calculated coefficients c0 to cm. Similarly, the coefficients c0 to cm (second data) are also calculated for the register 64 of the local oscillation circuit 13 by the above process (S701 and S702), and the control signal corresponding to the target frequency is output based on the calculated coefficients c0 to cm. Similarly, the coefficients c0 to cm (third data) are also calculated for the register 74 of the oscillation circuit 18 by the above process (S701 and S702), and the control signal corresponding to the target frequency is output based on the calculated coefficients c0 to cm.
Every time the target frequency is changed, the process of obtaining the coefficients c0 to cm (S701 to S703) can be performed to reduce effects of temperature changes.
When the target frequency is changed, the coefficients c0 to cm already stored in the memory can be used to perform the process of outputting the control signal (S704 and S705) without performing the process of obtaining the coefficients c0 to cm (S701 to S703) again. As a result, when the target frequency is changed, the oscillation frequency can rapidly be changed to the target frequency.
An embodiment of the present invention has been described. As described above, the least-square method can be used to rapidly determine the value of the control signal corresponding to the target frequency. Specifically, if the approximate curve showing the frequency characteristic of the oscillation circuit is the mth order, the coefficients c0 to cm are calculated by sampling for m+1 times to determine the value of the control signal corresponding to the target frequency based on the calculated coefficients c0 to cm. For example, if the order of the approximate curve of the frequency characteristic is the second order, while the value of the control signal must be changed up to 255 times in the method of changing the value of the control signal stepwise within the variable range, the value of the control signal corresponding to the target frequency can be determined in this embodiment by changing the value of the control signal only three times.
The coefficients c0 to cm can be obtained every time the target frequency is changed to reduce effects of temperature changes.
When the target frequency is changed, the oscillation frequency can rapidly be changed to the target frequency by using the coefficients c0 to cm already stored in the memory to determine the value of the control signal.
By determining the value of the control signal setting the tuning frequency of the high-frequency tuning circuit 11 to the target frequency in accordance with the process shown in
Similarly, by determining the value of the control signal setting the oscillation frequency of the local oscillation circuit 13 to the target frequency in accordance with the process shown in
By determining the value of the control signal setting the oscillation frequency of the oscillation circuit 18 to the target frequency in accordance with the process shown in
The above embodiments of the present invention are simply for facilitating the understanding of the present invention and are not in any way to be construed as limiting the present invention. The present invention may variously be changed or altered without departing from its spirit and encompass equivalents thereof.
Although the adjustment of the oscillation frequency of the oscillation circuit included in, for example, the FM radio receiver 1 has been described in an embodiment, the oscillation frequency can also be adjusted in an oscillation circuit included in an AM radio receiver as is the case with this embodiment. Although the control signal is, for example, eight bits in an embodiment, the control signal may be other than eight bits.
Number | Date | Country | Kind |
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2006-110880 | Apr 2006 | JP | national |