Radio receiver capable of correcting the field strength measurement of a radio signal

Abstract: In a radio receiver for receiving a particular radio signal of a particular frequency with an electric field strength among a plurality of radio signals of different frequencies, a temperature detector (31, 32) produces a detected temperature signal representative of an ambient temperature of the radio receiver. A correcting signal producing unit (33) produces a correcting signal representative of a control value determined by the detected temperature signal and a particular control signal produced by a frequency controller (11) to indicate a local frequency for the particular frequency. A correcting unit (34) corrects, according to the correcting signal, an electric field strength signal which is produced by an electric field strength detector (13) to represent the electric field strength detected in a detected signal produced by a detector (12) by detecting the particular radio signal in response to the particular control signal.

Description: This invention relates to a radio receiver and a method for receiving a particular radio signal of a particular frequency with an electric field strength among a plurality of radio signals of different frequencies. A well known radio receiver, eg a double superheterodyne receiver, includes a frequency controller for producing a particular control signal indicative of a local frequency. A detector detects the particular radio signal in response to the particular control signal to produce a detected signal. An electric field strength detector can be supplied with the detected signal. The electric field strength detector detects the electric field strength to produce an electric field strength signal representative of the electric field strength. As will later be described more in detail, the known radio receiver is defective in that the electric field strength detector cannot correctly detect the electric field strength. We have appreciated that this is because the detector has both a frequency characteristic and a temperature characteristic and produces the detected signal with gains which depend upon the particular frequency and ambient temperature of the radio receiver. United Kingdom Patent Specification GB-A-2 155 712 describes a radio signal strength indicator for an FM radio receiver. Temperature sensitivity of the radio signal strength indicator is compensated by the use of a differential amplifier which is supplied with a reference signal that also varies as a function of the ambient temperature. Our Japanese Laid-Open Patent Publication JP-A-2 285 817 (abstracted at Patent Abstracts of Japan Vol.15, No.58, Group E-1032, 12 February 1991) describes a radio transmitter which provides a control signal to correct a reference voltage in response to changes in the transmission frequency and in temperature. The present invention is defined in the appended claims, to which reference should now be made. The invention is described in detail, by way of example, with reference to the drawings, in which:- Fig. 1 is a block diagram of a known radio receiver; Fig. 2 shows at (A) a graph illustrative of the frequency characteristic of a detector and at (B) a graph which shows the temperature characteristic of the detector; Fig. 3 is a block diagram of a radio receiver according to an embodiment of this invention; and Fig. 4 is a flowchart for use in describing operation of the radio receiver illustrated in Fig. 3. Referring to Fig. 1, a known radio receiver will first be described in order to facilitate an understanding of the present invention. The radio receiver is capable of receiving a particular radio signal of a particular frequency with a specific electric field strength among a plurality of radio signals having different frequencies and received with field strengths which may be different from the specific electric field strength. In Fig. 1, the radio receiver is a double superheterodyne receiver for use typically as an ordinary radio receiver, a mobile telephone set, or an MCA (multichannel access) radio receiver. The illustrated radio receiver includes a frequency controller (F CONTROL) 11 for producing a particular control signal indicative of a local frequency for use in the double superheterodyne. A first detector (DET) 12 is for detecting the particular radio signal in response to the particular control signal to produce a detected signal in the manner which will presently be described in detail. An electric field strength detector (F STRENGTH) 13 is supplied with the detected signal for detecting the electric field strength to produce an electric field strength signal DC having an amplitude representative of the electric field strength. Generally, the electric field strength detector detects the amplitude of the detected signal and produces a direct voltage signal as the electric field strength signal. The first detector 12 comprises an RF (radio frequency) amplifier 14 connected to an antenna for amplifying the radio signals of the plurality in number, which signals are received at the antenna as received radio signals. A first local oscillator (LOC) 15 is connected to the frequency controller 11 for producing a first local signal in accordance with the particular control signal. A first mixer (MIX) 16 is connected to the RF amplifier 14 and to the first local oscillator 15 for producing a first IF (intermediate frequency) signal. An IF filter 17 is connected to the first mixer 16 for filtering the first IF signal. A second local oscillator 18 is for producing a second local signal. A second mixer 19 is connected to the IF filter 17 and to the second local oscillator 18 for producing a second IF signal. An IF amplifier 20 is connected to the second mixer 19 for amplifying the detected signal into an amplified detected signal. A second detector 21 is connected to the IF amplifier 20 for detecting and demodulating the amplified detected signal to produce a demodulated signal DEM as original intelligence, such as a sound signal or a data signal. Referring to Fig. 2 at (A), the first detector 12 has a frequency characteristic depicted as a gain G versus a frequency F. It will be assumed that the first detector 12 is operable in a frequency band B. Fig. 2 at (B) shows a temperature characteristic again as a gain G versus ambient temperature AT of the radio receiver. The first detector 12 is operable in a temperature range R. The detected signal has distortion corresponding to the particular frequency and the ambient temperature. The electric field strength detector 13 detects an electric field strength with the distortion. As a result, the conventional radio receiver is defective in that the electric field strength detector 13 can not correctly detect the electric field strength. Referring to Fig. 3, the description will proceed to a radio receiver according to a preferred embodiment of this invention. The radio receiver includes all of the components of the radio receiver of Fig. 1, which will not therefore be described again. In this case, the output of the field strength detector 13 is labelled DC'. The radio receiver is put in operation in an ambient temperature and additionally comprises a temperature sensor 31, depicted by a small circle, for detecting the ambient temperature of the radio receiver to produce a sensed temperature signal representative of the ambient temperature. A temperature detector (T DET) 32 is supplied with the sensed temperature signal to produce a detected temperature signal. A correcting signal producing unit 33 is connected to the frequency controller 11 and to the temperature detector 32 to produce a correcting signal representative of a control value determined by the particular control signal and the detected temperature signal. A correcting unit 34 is connected to the electric field strength detector 13 and to the correcting signal producing unit 33 for correcting the electric field strength signal DC' in accordance with the correcting signal. The correcting signal producing unit 33 comprises an A/D (analog-to-digital) converter 35 connected to the temperature detector 32 to convert the detected temperature signal into a digital temperature signal. A CPU (central processing unit) 36 is connected to the A/D converter 35 and to the frequency controller 11 to produce a digital correcting signal. A D/A (digital-to-analog) converter 37 is connected to the CPU 36 to convert the digital correcting signal to an analog correcting signal as the correcting signal. In a manner which will become clear in the following, the CPU comprises a first memory area for memorizing a plurality of frequency control values in correspondence to a plurality of control signals in accordance with a frequency characteristic in Fig. 2 at (A). A second memory area is for memorizing a plurality of temperature control values in correspondence to a plurality of temperature signals in accordance with a temperature characteristic in Fig. 2 at (B). A first memory reader is connected to the frequency controller and to the first memory area for reading out of the first memory area as a first read-out value one of the frequency control values that corresponds to the particular control signal. A second memory reader is connected to the temperature detector and to the second memory area for reading out of the second memory area as a second read-out value one of the temperature control values that corresponds to the detected temperature signal. An adder is connected to the first and second memory readers for producing, as the digital correcting signal, a sum signal representative of a sum of the first and the second read-out values. In Fig. 3, the correcting unit 34 comprises an operational amplifier 38 for adding the correcting signal to the electric field strength signal to produce a corrected electric field strength signal DC. Referring to Fig. 4, operation of the CPU will be described. The CPU 36 is supplied with the particular control signal and the digital temperature signal. In a first step St1, the CPU 36 retrieves a received channel according to the particular control signal in the first memory area. In a step St1a, the CPU 36 judges whether the received channel is within the limits of a predetermined band. Similarly, in steps St1b and St1c the CPU 36 judges whether the received channel is within the limits of preselected ranges, respectively. In a second step St2, the first memory reader reads out one of the frequency control values as a first read-out value TC from the first memory area in the CPU 36. It will be assumed that the different frequencies are first, second, third, and fourth frequencies f A , f B , f C , and f D (f A < f B < f C < f D ) and that the first through the fourth frequencies f A , f B , f C , and f D are allocated to channels Ach, Bch, Cch, and Dch. If a received channel Rch is Ach ≦ Rch < Bch, the first read-out value TC is equal to TC1 in the manner depicted at a step St2a. If the received channel Rch is Bch ≦ Rch < Cch, the first read-out value TC is equal to TC2 in the manner illustrated at a step St2b. If the received channel Rch is Cch ≦ Rch < Dch, the first read-out value TC becomes equal to TC3 as illustrated at a step St2c. In a third step St3, the CPU 36 retrieves the ambient temperature according to the digital temperature signal in the second memory area. In a step St3a, the CPU 36 judges whether the ambient temperature AT is within the limits of a predetermined temperature range. Similarly, in steps St3b and St3c the CPU 36 judges whether the received channel is within the limits of prescribed temperature ranges, respectively. In a fourth step St4, the second memory reader reads out one of the temperature control value as a second read-out value TM. It will be presumed that typical temperatures are represented by t1, t2, t3, and t4 (t1 < t2 < t3 < t4). If an ambient temperature AT is t1 ≦ AT < t2, the second read-out value TM is equal to TM1 in the manner depicted at a step St4a. If the ambient temperature AT is t2 ≦ AT < t3, the second read-out value TM is equal to TM2 in the manner illustrated at a step St4b. If the ambient temperature AT is t3 ≦ AT < t4, the second read-out value TM becomes equal to TM3 as illustrated at a step St4c. In a fifth step St5, the adder produces as the digital correcting signal, a sum signal representative of a sum RC of the first and the second read-out values TC and TM. In a sixth step St6, the adder supplies the digital correcting signal to the D/A converter 37. The D/A converter 37 supplies the analog correcting signal as the correcting signal to the correcting unit 34. The correcting unit 34 corrects the electric field strength signal DC′ according to the correcting signal and produces the corrected electric field strength signal DC.

Claims: A radio receiver for receiving a particular radio signal of a particular frequency with an electric field strength among a plurality of radio signals of different frequencies, the radio receiver including a frequency controller (11) for producing a particular control signal indicative of a local frequency, a detector (12) for detecting the particular radio signal in response to the particular control signal to produce a detected signal, and an electric field strength detector (13) supplied with the detected signal for detecting the electric field strength to produce an electric field strength signal representative of the electric field strength, the radio receiver comprising: temperature detecting means (31,32) for detecting the ambient temperature of the radio receiver to produce a detected temperature signal representative of the ambient temperature; correcting signal producing means (33) connected to the frequency controller (11) and to the temperature detecting means (31,32) for producing a correcting signal representative of a control value determined by both the particular control signal and the detected temperature signal; and correcting means (34) connected to the electric field strength detector (13) and to the correcting signal producing means (33) for correcting the electric field strength signal in accordance with the correcting signal; the correcting signal producing means (33) comprising: a primary memory area for memorizing a plurality of frequency control values in correspondence to a plurality of control signals; primary reading means connected to the frequency controller and to the primary memory area for reading out of the primary memory area as a primary read-out value one of the frequency control values that corresponds to the particular control signal for producing the primary read-out value; a secondary memory area for memorizing a plurality of temperature control values in correspondence to a plurality of detected temperature signals; secondary reading means connected to the temperature detecting means and to the secondary memory area for reading out of the secondary memory area as a secondary read-out value one of the temperature control values that corresponds to the detected temperature signal and for producing the secondary read-out value; and adding means connected to the primary reading means and to the secondary reading means for adding the primary read-out value and the secondary read-out value to provide the correcting signal. A method of receiving a particular radio signal of a particular frequency with an electric field strength among a plurality of radio signals of different frequencies, the method including the steps of: producing a particular control signal indicative of a local frequency, detecting the particular radio signal in response to the particular control signal to produce a detected signal, and detecting the electric field strength in the detected signal to produce an electric field strength signal representative of the electric field strength, the method further comprising the steps of: detecting the ambient temperature of the radio receiver to produce a detected temperature signal representative of the ambient temperature; producing a correcting signal representative of a control value determined by both the particular control signal and the detected temperature signal; and correcting the electric field strength signal in accordance with the correcting signal; the step of producing a correcting signal comprising: memorizing in a primary memory area a plurality of frequency control values in correspondence to a plurality of control signals; reading out of the primary memory area as a primary read-out value one of the frequency control values that corresponds to the particular control signal for producing the primary read-out value; memorizing in a secondary memory area a plurality of temperature control values in correspondence to a plurality of detected temperature signals; reading out of the secondary memory area as a secondary read-out value one of the temperature control values that corresponds to the detected temperature signal and for producing the secondary read-out value; and adding the primary read-out value and the secondary read-out value to provide the correcting signal.

Inventors: MIYAZAKI SHINICHI, MIYAZAKI, SHINICHI, MIYAZAKI, SHINICHI, C/O NEC CORPORATION
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1992
Main classification: H04B1
IPC codes: H04B1