JPH05291853A - Variable gain control circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] Even if strong intermodulation due to multiple interfering waves is occurring, accurate variable gain control operation can be performed on the received high frequency signal, and this can be achieved with a small current consumption. Thus, a variable gain control circuit is provided particularly effectively when used in a mobile wireless device using a battery power source. A local oscillator circuit 50 generates an oscillation signal having a frequency lower than that of the local oscillation signal for converting the received high frequency signal into a baseband signal, and the oscillation signal is mixed with the received high frequency signal after the level is changed. The intermediate frequency signal for generating the variable gain control signal is conveniently generated by mixing at 60a. Then, the intermediate frequency signal is fed to the amplifier 60.
A gain control signal is generated by amplifying it in b and then rectifying it in the rectifier circuit 60c, and supplying this gain control signal to the variable attenuator 32 to variably control its attenuation amount.
The level of the received high frequency signal is made variable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable gain control provided in a mobile radio communication device such as a selective call receiver, a portable radio telephone, a cordless telephone, etc., which employs a direct conversion reception system as a reception demodulation system. Regarding the circuit.

[0002]

2. Description of the Related Art Recently, in metropolitan areas and the like, a plurality of carriers have entered a common service area to provide mobile radio communication services such as a selective call service and a car / mobile radio telephone service. .. In such an area, since a base station is installed for each carrier in a common service area to perform transmission, for example, when a mobile radio device receiving the service of company A moves near a base station of another company, There may be a so-called D / U inversion state in which the reception level of the interfering wave is higher than the reception level of the desired wave. Furthermore, when a mobile radio receives a plurality of interfering waves in such a situation, the intermodulation (IM) of these interfering waves significantly deteriorates the reception characteristics of the mobile radio, and even if the reception level of the desired wave is Even if there is enough, the desired wave may not be received correctly.

Therefore, a variable gain control circuit (AG) is commonly used in a receiving circuit system of a mobile radio used in such an area.
C circuit) is provided. FIG. 7 shows the configuration of a receiving circuit system of a conventional mobile radio device equipped with an AGC circuit.
1 illustrates a mobile wireless device that employs a double superheterodyne reception system.

In FIG. 1, a received high frequency signal received by an antenna 11 passes through a variable attenuator 12, is amplified by a high frequency amplifier 13, and is then passed through a high frequency band pass filter 14.
And is input to the first frequency mixer 15. In the first frequency mixer 15, the received high frequency signal is mixed with the first local oscillation signal output from the first local oscillation circuit 16, and thereby the frequency is converted into the first intermediate frequency signal. The first local oscillation circuit 16 uses a frequency synthesizer, and compares the reference frequency generated from the reference oscillator 16a with the frequency corresponding to the oscillation output frequency fed back from the voltage controlled oscillator (VCO) 16d. The phase comparison is performed by the device (PD) 16b. Then, a DC voltage corresponding to the comparison output is generated by the loop filter 16c and is supplied to the VCO 16d, whereby the VCO 16d
To generate a first local oscillation signal by frequency-multiplying this oscillation signal by a multiplier (MLT) 16e.

The first intermediate frequency signal passes through the first intermediate frequency filter 17 and then is input to the second frequency mixer 18. In the second frequency mixer 18, the second intermediate frequency signal generated by the second local oscillation circuit 19 is used as the second intermediate frequency signal.
The frequency is converted into a second intermediate frequency signal by being mixed with the local oscillation signal. The second intermediate frequency signal is passed through the second intermediate frequency filter 20 and then input to the detection circuit 21. In the detection circuit 21, the second intermediate frequency signal is amplified by the intermediate frequency amplifier 21a, detected by the detector 21b, and the detected output is filtered by the data filter 21c and then output as a demodulated signal.

The second intermediate frequency signal output from the second intermediate frequency filter 20 is amplified by an amplifier 22 and then rectified by a rectifier circuit 23 to become a DC voltage. This DC voltage is a gain control signal (AGC). Signal) to the variable attenuator 12. As a result, the amount of attenuation of the variable attenuator 12 is controlled, whereby the signal level of the received high frequency signal is changed.

With such a configuration, when a plurality of interfering waves having a high received electric field strength are received, intermodulation occurs between these interfering waves, and the interfering waves fall into the receiving frequency, the second intermediate frequency signal As the signal level increases, AGC
The signal level becomes high, which increases the amount of attenuation of the variable attenuator 12. Therefore, the signal level of the received high frequency signal is reduced, and thereby the influence of IM interference due to the plurality of interference waves is reduced.

On the other hand, recently, in order to further reduce the size of mobile radio devices, a direct conversion reception system (DCR system) has attracted attention in place of the above-mentioned super heterodyne reception system. FIG. 8 shows an example of the configuration of a receiving circuit system of a mobile radio adopting the DCR method.
In the figure, the received high frequency signal received by the antenna 31 is passed through the variable attenuator 32, high frequency amplified by the high frequency amplifier 33, and then filtered by the high frequency filter 34. The received high-frequency signal output from the high-frequency filter 34 is branched into two and then mixed by the mixer 3.
5, 36 are input. Also, these mixers 35, 36
Two local oscillation signals, which are respectively output from a local oscillation circuit (not shown) and then provided with a phase shift difference of π / 2, are input by the phase shifter 37. Then, in the mixers 35 and 36, the received high frequency signal is mixed with the two local oscillation signals and converted into a baseband signal. The received baseband signals output from the mixers 35 and 36 are input to a detector (not shown) after passing through the baseband filters 38 and 39, and the detector outputs digital signals of "1" and "0". Demodulated to data.

By the way, as an AGC circuit provided in this type of DCR mobile radio, for example, the following circuit is considered. That is, as shown in FIG.
The reception baseband signal output from one of the two mixers 35 and 36 is amplified by the amplifier 40 and then rectified by the rectification circuit 41, whereby the reception baseband signal has the signal level. A corresponding DC voltage can be obtained. Then, this DC voltage is supplied to the variable attenuator 32 as an AGC signal, whereby the attenuation amount of the variable attenuator 32 is controlled. That is, when the received wave is the FSK modulated wave, the level of the received baseband signal linearly changes with respect to the level of the received wave unless the high frequency amplifier 33 and the mixer 36 are saturated. Therefore, if the level of the received baseband signal is detected and the attenuation amount of the variable attenuator is changed, AGC can be applied to the received high frequency signal.

However, the circuit for performing AGC based on such a received baseband signal has the following problems. That is, when a plurality of interfering waves with high received electric field strength are received and IM is generated, the reception signals of these interfering waves are in a state of being subjected to uncorrelated modulation. Therefore, IM
When the degree of interference increases, the level of the received baseband signal becomes not proportional to the received level of the interfering wave, and as a result, the accurate AG based on the level of the received baseband signal is obtained.
It was difficult to play C.

Further, as another AGC circuit provided in a DCR type mobile radio device, for example, a received high frequency signal output from a high frequency amplifier 33 as shown in FIG.
In some cases, the signal is input to the rectifier circuit 43 via 2 and rectified by the rectifier 43 to obtain a DC voltage according to the level of the received high frequency signal. With such a circuit, it is possible to accurately detect the level of the received wave and perform the AGC even if the received high frequency signal has an IM fault due to the interfering wave. However, this type of circuit requires a high frequency amplifier as the amplifier 42 for generating the AGC signal.
Another problem is that the current consumption of the circuit becomes very large. This problem is extremely unfavorable, especially in a mobile wireless device that uses a battery as a power source because it leads to a reduction in usage time or an increase in the weight of the wireless device due to an increase in battery capacity.

[0012]

As described above, in the variable gain control circuit conventionally considered for the mobile radio equipment of the direct conversion receiving system, the strong I
When an M fault occurs, accurate AGC cannot be performed, and the circuit consumes a large amount of current to shorten the communication time or increase the size and weight of the wireless device.

The present invention has been made in view of the above circumstances, and an object thereof is to perform a variable gain control operation accurately for a received high frequency signal even when strong intermodulation due to a plurality of interfering waves occurs. It is possible to realize this with a small current consumption, thereby providing a variable gain control circuit particularly effectively when used in a mobile radio device using a battery power supply.

[0014]

In order to achieve the above object, the present invention provides a radio receiver adopting a direct conversion receiving system in which a received high frequency signal is directly frequency-converted into a baseband signal by a frequency conversion means for detection. In the variable gain control circuit provided, variable gain type level varying means for varying and outputting the level of the received high frequency signal is inserted in the signal path of the received high frequency signal and supplied to the frequency conversion means. An oscillation signal having a frequency lower than that of the local oscillation signal generated by the oscillation means, and the oscillation signal is mixed with the received high-frequency signal after the level adjustment outputted from the level adjustment means to obtain an intermediate frequency for variable gain control. A signal is generated, the signal level of the intermediate frequency signal is detected, and the level varying means of the level varying means detects the signal level according to the detected signal level. Give is obtained so as to variably control.

[0015]

As a result, according to the present invention, the variable gain control signal is generated based on the received high frequency signal without using the received baseband signal to generate the signal for variably controlling the gain of the level changing means. Even when intermodulation of a plurality of interfering waves occurs in the received high frequency signal, it is possible to perform accurate variable gain control without being affected by the intermodulation. Further, when generating the variable gain control signal, for convenience, a local oscillation signal is generated to frequency-convert the received high frequency signal into an intermediate frequency signal, and the variable gain control signal is generated based on the level of the intermediate frequency signal. As a result, it becomes possible to use an intermediate frequency amplifier instead of a high frequency amplifier as an amplifier for generating the variable gain control signal. Therefore, the current consumption of the circuit can be kept small compared to the case of using a high frequency amplifier, which suppresses the consumption of the battery and extends the continuous use time when a battery power source is used. Alternatively, the battery capacity can be kept small to allow the radio to be smaller and lighter.

[0016]

EXAMPLES The present invention will be described below based on examples.

FIG. 1 is a circuit block diagram showing a configuration of a receiving circuit system of a mobile radio equipped with a variable gain control circuit according to an embodiment of the present invention. In addition, in FIG.
The same parts as those in FIG.

In FIG. 1, reference numeral 50 is a local oscillation circuit,
The local oscillator circuit 50 is composed of a frequency synthesizer. That is, the oscillation output signal generated from the voltage controlled oscillator (VCO) 50d that constitutes a part of the PLL is fed back to the phase comparator (PD) 50b, where it is in phase with the reference signal generated from the reference oscillator 50a. Be compared. Then, a DC voltage corresponding to the phase difference detected by the phase comparator 50b is output from the loop filter 50c, and an oscillation output signal fvco is generated from the VCO 50d according to the DC voltage. This oscillation output signal fvco is
In the frequency multiplier (MLT) 50e, the frequency is multiplied by a predetermined multiplication number (for example, 5 times) to generate the first local oscillation signal 5
It becomes fvco and is supplied to the mixers 35 and 36 as a signal for frequency-converting the received high frequency signal into a baseband signal.

In the frequency multiplier 50e, the V
The oscillation output signal fvco generated from the CO 50d is frequency-multiplied by another multiplication number (for example, 4 times), thereby generating the second local oscillation signal 4fvco having a lower frequency than the first local oscillation signal 5fvco. .. This second local oscillation signal 4fvco is used as a signal for generating a variable gain control signal.

On the other hand, 60 is a variable gain control signal generating circuit for generating a signal for variably controlling the amount of attenuation of the variable attenuator 32. This circuit 60 is a mixer 60a and an amplifier 6
0b and a rectifying circuit 60c. The mixer 60a receives the received high frequency signal output from the high frequency filter 34 as shown in FIG.
The coarse coupling is input via. And in the mixer 60a,
The second received high frequency signal is output from the multiplier 50e
Is mixed with the local oscillation signal 4fvco and converted into an intermediate frequency signal. At this time, since the frequency of the received high frequency signal corresponds to 5fvco, the frequency of the intermediate frequency signal output from the mixer 60a is 5fvco-4fvco = fvco.

The intermediate frequency signal output from the mixer 60a is amplified by the amplifier 60b which is an intermediate frequency amplifier and is input to the rectifier circuit 60c. The rectifier circuit 60c rectifies the intermediate frequency signal output from the amplifier 60b, thereby outputting a DC voltage corresponding to the amplitude level of the intermediate frequency signal. This DC voltage is supplied to the control input terminal of the variable attenuator 32 as a gain control signal.

With such a configuration, in the variable gain control signal generation circuit 60, the received high frequency signal and the AG generated from the frequency multiplier 50e of the local oscillation circuit 50 are generated.
The second local oscillation signal for C is mixed by the mixer 60a to be converted into an intermediate frequency signal, and the intermediate frequency signal is amplified by the amplifier 60b and then rectified by the rectifier circuit 60c. Is generated. Then, the amount of attenuation of the variable attenuator 32 is variably controlled by this gain control signal. That is, in the variable gain control signal generation circuit 60,
A reception intermediate frequency signal that is not generated in the receiving circuit system of the direct conversion reception system is conveniently generated, and a variable gain control signal is generated based on the level of this intermediate frequency signal.

Therefore, even if the received high frequency signal has an IM fault due to a plurality of interfering waves having a large received electric field strength,
AGC can be performed by accurately detecting the level of the received wave. Therefore, it is possible to appropriately reduce the reception level of the interfering wave while the interfering wave having a high level is being received.
The influence of M interference can be reduced and the desired wave can be received stably. Further, since the intermediate frequency amplifier can be used as the amplifier 60b of the variable gain control signal generating circuit 60, the current consumption by the amplifier 60b can be reduced as compared with the case where the high frequency amplifier is used. Therefore, it is possible to extend the battery life by reducing the current consumption, thereby achieving at least one of the extension of the continuous use time of the radio device and the reduction in the size and weight of the radio device due to the reduction in the battery capacity. ..

The present invention is not limited to the above embodiment. For example, in the above embodiment, one frequency multiplier 50e is used to generate the first local oscillation signal for baseband conversion and the second local oscillation signal for AGC signal generation. As described above, a second frequency multiplication circuit 61d is provided separately from the first frequency multiplier 51e for generating the first local oscillation signal, and the second frequency multiplication circuit 61d is used to generate a second local portion for AGC signal generation. It may be configured to generate an oscillating signal. According to this structure, it is possible to generate the first and second local oscillation signals having good waveform characteristics which do not include the frequency component of the local oscillation signal of the other party, and to obtain a signal having a sufficiently high signal level. be able to.

Further, in FIG. 1, the first and second local oscillation signals generated from the frequency multiplier 50e are passed through filters, respectively, whereby the frequency unity of the first and second local oscillation signals is improved. You may make it improve further. Further, a tuning circuit is provided, and the tuning circuit allows the second
The local oscillation signal may be extracted.

Further, in the above embodiment, the received high frequency signal for input to the variable gain control signal generating circuit 60 is shown in FIG.
Although the capacitor 44 is taken out by the coarse coupling as shown in FIG.
The received high frequency signal leaking to the power supply lines 5 and 36 may be taken out and input to the variable gain control signal generation circuit 60.

In the above embodiment, the variable attenuator 32 is provided between the antenna 31 and the high frequency amplifier 33, but as shown in FIG. 6, the variable attenuator is provided between the high frequency amplifier 33 and the high frequency filter 34. The container 302 may be provided. Further, in the above embodiment, the level of the received high frequency signal is varied by variably controlling the attenuation amount of the variable attenuator 32. However, as shown in FIG. 5, the output from the rectifying circuit 60c of the variable gain control signal generating circuit 60 The bias voltage of the high frequency amplifier 303 may be variably controlled by the generated AGC signal, and the amplification factor of the high frequency amplifier 303 may be variably controlled to change the level of the received high frequency signal. With this configuration, the variable attenuator can be eliminated, and the circuit configuration can be simplified accordingly. Further, a variable gain amplifier may be provided instead of the variable attenuator, and the amplification factor of this variable gain amplifier may be variably controlled by the AGC signal.

In addition, the configuration of the variable gain control signal generating circuit, the configuration of the oscillation signal generating means used to generate the variable gain control signal, the type of radio equipment to be applied, the circuit configuration thereof, and the like are also included in the present invention. Various modifications can be made without departing from the scope of the invention.

[0029]

As described in detail above, according to the present invention, the oscillating means generates an oscillating signal having a frequency lower than that of the local oscillating signal for converting the received high frequency signal into the base band signal, and the oscillating signal is leveled. An intermediate frequency signal for generating a variable gain control signal is generated by mixing with the received high frequency signal after the variable, and a variable gain control signal is generated based on the signal level of this intermediate frequency signal to variably control the gain of the level changing means. By doing so, the level of the received high frequency signal is made variable.

Therefore, according to the present invention, the variable gain control operation can be accurately performed on the received high frequency signal even when strong intermodulation is generated by a plurality of interfering waves, and this is realized with a small current consumption. This makes it possible to provide a variable gain control circuit that is particularly effective when used in a mobile wireless device using a battery power supply.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing a configuration of a receiving circuit system of a mobile radio device including a variable gain control circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a reception high frequency signal extraction circuit in the circuit shown in FIG.

FIG. 3 is a circuit block diagram showing a configuration of a receiving circuit system of a mobile radio device including a variable gain control circuit according to another embodiment of the present invention.

FIG. 4 is a diagram showing another configuration example of a reception high-frequency signal extraction circuit.

FIG. 5 is a diagram showing another configuration example of a circuit that varies the level of a received high frequency signal.

FIG. 6 is a diagram showing another insertion position of the variable attenuator.

FIG. 7 is a circuit block diagram showing a configuration example of a receiving circuit system of a superheterodyne mobile radio device including a variable gain control circuit.

FIG. 8 is a circuit block diagram showing an example of a configuration of a conventional receiving circuit system of a direct conversion type mobile radio device including a variable gain control circuit.

FIG. 9 is a circuit block diagram showing another example of the configuration of a conventional receiving circuit system of a direct conversion type mobile radio device including a variable gain control circuit.

[Explanation of symbols]

31 ... Antenna, 32, 302 ... Variable attenuator, 33, 3
03 ... High frequency amplifier, 34 ... High frequency filter, 35, 3
6 ... Mixer for baseband conversion, 37 ... Phase shifter, 50
... local oscillator circuit, 50a, 51a ... reference oscillator, 50
b, 51b ... Phase comparator (PD), 50c, 51c ... Loop filter, 50d, 51d ... Voltage controlled oscillator (VC)
O), 50e, 51e, 61d ... Frequency multiplier (ML)
T), 60 ... Variable gain control signal generating circuit, 60a ... Mixer for generating variable gain control signal, 60b ... Amplifier, 60c
… Rectifier circuit.

Claims (1)

[Claims] 1. A variable gain control circuit provided in a radio receiver adopting a direct conversion reception system in which a received high frequency signal is directly frequency-converted into a baseband signal by a frequency conversion means and detected. And a variable gain type level varying means for varying and outputting the level of the received high frequency signal, and a second local oscillation whose frequency is lower than that of the first local oscillation signal supplied to the frequency converting means. Oscillating means for generating a signal, and mixing the level-varied received high frequency signal output from the level varying means with the second local oscillation signal generated by the oscillating means to obtain an intermediate frequency signal And the signal level of the intermediate frequency signal obtained by this frequency mixing means, Flip and variable gain control circuit, characterized by comprising a gain control means for variably controlling the gain of said level varying means.