JPH0879125A - Reception circuit - Google Patents

Abstract

PURPOSE: To improve interference characteristics in a portable telephone set by performing control to fix the output of an intermediate frequency filter by an automatic gain control means when the level of reception signal exceeds a prescribed value. CONSTITUTION: When the output signal of an IF filter 10 is increased, the automatic gain control means 8 attenuates the level of IF signals 7 being the output of a mixer 6 to fix the output level of the filter 10. In this case, in the control means 8, the output signal level of the filter 10 is detected by a level detection circuit 8a and the detection signal level is smoothed in a capacitor C2 and transmitted to a control circuit 8b. Then, a control current is sent out from the circuit 8b to an attenuator 8c and the output signals of the mixer 6 are attenuated to let the output signal level of the filter 10 be the prescribed value and are transmitted to the filter 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver circuit, and more particularly to a mobile phone.

[0002]

2. Description of the Related Art Generally, a conventional receiving circuit used in a mobile phone or the like has a structure shown in FIG. In FIG. 5, the received signal received via the antenna is RF (Radio
Frequency) is amplified in the amplifier 4, mixed with the local signal 5 in the mixer 6, and converted into the intermediate frequency signal 7. Here, the intermediate frequency signal 7 is a signal having a frequency that is the difference between the received signal and the local signal 5, and is a signal having a lower frequency than the received signal. The intermediate frequency signal 7 that is the output of the mixer 6 is filtered by a bandpass filter 10 that is an IF (Intermediate Frequency) filter (also called an intermediate frequency filter), and only the signal of the reception channel is passed, and the signals other than the reception channel are blocked. To be done. The output signal of the bandpass filter 10 is the IF amplifier 12
Is amplified, FM-detected by the FM detection circuit 16, and demodulated and output as an audio signal.

A signal level detection circuit 14 for detecting the input signal level of the IF amplifier 12 is connected to the IF amplifier 12, and the detected signal is smoothed by a capacitor C1 and becomes a signal level detection output 15. This detection output 15 is normally a voltage proportional to the input signal level (the signal level of the reception signal received via the antenna 2), and the level of the detection output 15 when the receiving circuit is used in a mobile phone. The base station is switched according to

[0004]

However, the signal level detection circuit 14 used in such a conventional receiving circuit has a unique detection range, and as shown in FIG. 6, the input signal level is a predetermined value V _0. When it becomes the above, it has the characteristic g ₁ that the detection output becomes constant. And IF amplifier 1
Since the signal input to 2 is the signal amplified by the RF amplifier 4 and the mixer 6, the signal level detection circuit 1
The detection output range of 4 is narrower when viewed from the input of the antenna 2. For example, if the upper limit of the detection level of the signal level detection circuit is 100 dBμV (100 mVr.ms) and the gains of the RF amplifier 4 and the mixer 6 are 20 dB, the upper limit of the detection level seen from the input of the antenna 2 is 100-.
(20 × 2) = 60 dBμV (1 mVr.ms), which is narrow.

On the other hand, in the mobile phone, a) the gain of the RF amplifier 4 is lowered in order to improve the interference characteristic in the case of a strong electric field (when the signal of the channel other than the currently used channel is strong), and b) reception. When the signal is strong (when the base station is close), the transmission power is reduced in order to prolong the battery life as long as possible.

Therefore, when the detection range of the signal level detection circuit 14 is narrow as in the conventional case and the detection output becomes constant when the input signal level becomes a predetermined value or more, even if an attempt is made to improve the interference characteristic in a strong electric field. It was unclear how much the gain of the RF amplifier 4 should be lowered, or how much the transmission power could be lowered when the received signal was strong. For this reason, there is a problem that the interference characteristic is not improved in a strong electric field, or when the received signal is strong, the battery power is wasted and the battery life is shortened.

Further, although an external ceramic filter is usually used for an IC chip in the IF filter 10, considering the case where an active filter is used for the IF filter 10 and is built in the IC chip for use in a mobile phone, it is active. The filter is S / compared to the ceramic filter
Since the N-ratio is poor, the reception sensitivity becomes poor unless the total gain of the RF amplifier 4 and the mixer 6 is increased. Therefore, antenna 2
There was a problem that the upper limit of the detection level seen from the input of was even lower.

The present invention has been made in consideration of the above circumstances, and it is possible to improve the interference characteristic as much as possible when used in a mobile phone and to prolong the life of the battery as much as possible. It is an object of the present invention to provide a receiving circuit capable of performing

[0009]

First Amplification of Received Signal
Amplifying means, mixer means for outputting an intermediate frequency signal from the output signal of the first amplifying means and a local signal, an intermediate frequency filter for filtering the intermediate frequency signal, and an output signal of the intermediate frequency filter. Second amplification means,
The signal level detecting means for detecting the input signal level of the second amplifying means and the output of the intermediate frequency filter when the level of the received signal exceeds a predetermined value based on the output signal level of the intermediate frequency filter. Automatic gain control means for attenuating the signal level of either the output signal of the first amplifying means or the output signal of the mixer means so as to be a constant value and outputting a voltage signal according to the amount of attenuation; And a smoothing means for smoothing by adding the voltage signal from the automatic gain control means and the output of the signal level detecting means.

[0010]

According to the receiving circuit of the present invention having such a configuration, when the level of the received signal exceeds a predetermined value, the automatic gain control means makes the output of the intermediate frequency filter a constant value. The level of the output signal of the amplifying means or the mixer is attenuated. At this time, the voltage signal output from the automatic gain control means is added to the output of the signal level detection means by the addition smoothing means to be smoothed. If this smoothed signal level is used as the signal level detection output, the signal level detection output can have an upper limit larger than that in the case of the conventional receiving circuit, and has an interference characteristic when used in a mobile phone. It can be improved as much as possible, and the battery life can be extended as long as possible.

[0011]

FIG. 1 shows the configuration of an embodiment of a receiving circuit according to the present invention. The receiving circuit of this embodiment is the conventional receiving circuit shown in FIG. 5, in which automatic gain control means 8 and addition means 18 are newly provided. The automatic gain control means 8 controls the IF when the output signal of the IF filter 10 increases.
The mixer 6 keeps the output level of the filter 10 constant.
For attenuating the level of the intermediate frequency signal 7 which is the output of the above, and has a level detection circuit 8a, a control circuit 8b, an attenuator 8c, and a capacitor C2. The level detection circuit 8a detects the output signal level of the IF filter 10, and the detected signal level is the capacitor C
It is smoothed by 2 and sent to the control circuit 8b. When the smoothed signal level is equal to or higher than a predetermined value, that is, when the signal level of the IF filter 10 is equal to or higher than the predetermined value, a control current is sent from the control circuit 8b to the attenuator 8c to output the output signal level of the IF filter 10. The output signal of the mixer 10 is attenuated by the attenuator so as to have the above-mentioned predetermined value and is sent to the IF filter 10.

The control circuit 8b sends the voltage signal 9 according to the control current, that is, the voltage signal according to the amount of attenuation to the adding means 18. The voltage signal 9 from the control circuit 8b and the output signal 15 of the signal level detection circuit 14 are added by the adding means 18. The output of the adding means 18 is smoothed by the capacitor C1 and becomes the signal level detection output 19.

When the level of the input signal input through the antenna 2 is below a predetermined value, that is, when the output signal level of the IF filter 10 is below a predetermined value, the output signal 7 of the mixer 6 is automatically gain controlled. It is not attenuated by the means 8 and is sent to the IF filter 10 as it is. At this time, the voltage signal according to the control current output from the control circuit 8b becomes zero, so the characteristic of the attenuator 8c becomes the graph g ₂ shown in FIG.

On the other hand, when the level of the input signal input via the antenna 2 exceeds a predetermined value, the automatic gain control means 8 controls the output signal level of the IF filter 10 to a predetermined value (constant). Therefore, the characteristics of the output signal of the signal level detection circuit 14 are shown in the graph g ₁ shown in FIG.
Becomes This is the same as the characteristic graph g ₁ shown in FIG.

Therefore, the signal level detection output 19 obtained by this embodiment is the graph g ₃ which is the sum of the graphs g ₁ and g ₂ . As a result, the upper limit of the signal level detection output can be set larger than that of the conventional receiving circuit, and when used in a mobile phone, the interference characteristic can be improved as much as possible, and the battery The life can be extended as long as possible.

Next, FIG. 3 shows the configuration of a first concrete example of the mixer 6 and the attenuator 8b in the receiving circuit according to the above embodiment. In FIG. 3, the mixer 6 includes a first differential circuit including NPN transistors Q1 and Q2, and a second differential circuit including NPN transistors Q3 and Q4.
It is composed of a third differential circuit composed of NPN transistors Q5 and Q6, a constant current source I _01, and a variable current source I ₀₂ . The constant current source I ₀₁ and the variable current source I ₀₂ are connected to the commonly connected emitters of the transistors Q1 and Q2. The collector of the transistor Q1 is connected to the commonly connected emitters of the transistors Q3 and Q4 of the second differential circuit, and the collector of the transistor Q2 is connected to the commonly connected emitters of the transistors Q5 and Q6 of the third differential circuit. Has been done.

The signal sent from the RF amplifier 4 to the mixer 6 is input to the base of one of the transistors Q1 and Q2, and the local signal is the base of the transistors Q3 and Q6 or the transistor Q4.
And to the base of Q5. The output of the mixer 6 is output from the collectors of the transistors Q3 and Q5 and the collectors of the transistors Q4 and Q6. The output of the mixer 6 is sent to the attenuator 35 via a current mirror circuit composed of PNP type transistors Q7 to Q10. This attenuator 35 is a PNP transistor Q1.
It has a balanced circuit composed of 1, Q12, Q13, and Q14, a resistor R1, and a variable current source I ₀₃ .
Then, by increasing / decreasing the current of the variable current source I ₀₃ , the voltage drop of the resistor R1 is increased / decreased, whereby the attenuation amount is determined. When the current I ₀₃ of the variable current source I ₀₃ is high, a higher voltage drop of the resistor R1, collapses the balance of the balanced circuit, out the output to the output terminal via the transistor Q15, Q16 and resistors R2, the IF filter 10 Sent out. At this time, the amount of attenuation is “0”.

[0018] When relative current I ₀₃ of the variable current source I ₀₃ This "0", the voltage drop across the resistor R1 is "0", the balancing circuit is taken equilibrium, output to the output terminal Does not occur, and the amount of attenuation becomes infinite.

In the circuit shown in FIG. 3, the mixer 6 has an attenuator 31 composed of transistors Q1 and Q2, a constant current source I ₀₁ , and a variable current source I ₀₂ . The attenuation amount of the attenuator 31 is determined by the magnitude of the current I ₀₂ flowing through the variable current source I ₀₂ . Since the gain G _{vc of the} mixer 6 is proportional to the current (I ₀₁ + I ₀₂ ) flowing through the mixer, the attenuation is “0” when the current I ₀₂ is large, and the attenuation is I ₀₂ = 0. It will be the maximum.

Generally, unless the attenuation amount is set to about 20 dB per one stage of the attenuator, the linearity between the control signal of the attenuator and the attenuation amount becomes poor. However, with only 20 dB of attenuation, the amount of attenuation is small. Therefore, as shown in FIG.
By sending 5 to a plurality of locations, the attenuation amount is increased and the linearity between the control signal and the attenuation amount is improved.

The configuration of the second specific example of the mixer 6 and the attenuator 8b according to the receiving circuit of the above embodiment is shown in FIG.
Shown in The specific example shown in FIG. 4 is obtained by replacing the attenuation circuit 31 with an attenuation circuit 41 in the specific example shown in FIG. The attenuating circuit 41 includes a differential circuit including NPN transistors T1 and T2, resistors R3 and R4, and N.
It has a differential circuit composed of PN transistors T3 and T4, a constant current source I _01, and a variable current source I ₀₂ .
One ends of the resistors R3 and R4 are connected to the emitters of the transistors T1 and T2, respectively, and the other ends are commonly connected to the constant current source I ₀₁ . On the other hand, the transistor T3
The emitters of T4 and T4 are connected in common and the variable current source I
_It is connected to ₀₂ .

The specific example shown in FIG. 4 has the same effect as the specific example shown in FIG. 3 and has the effect that the dynamic range of the mixer input can be expanded.

In the above embodiment, the attenuator 8b of the automatic gain control means 8 is the mixer 6 and the IF filter 1.
Although it is provided between 0, it is needless to say that the same effect can be obtained by providing between the RF amplifier 4 and the mixer 6.

Further, in this embodiment, since the automatic gain control means 8 is provided, it is possible to prevent the IF filter 10 from being distorted even if an active filter is used as the IF filter 10.

[0025]

As described above, according to the present invention, it is possible to increase the upper limit of the signal level detection output, so that the interference characteristic is improved as much as possible when used in a mobile phone. In addition, the battery life can be extended as long as possible.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of a receiving circuit according to the present invention.

FIG. 2 is a graph illustrating the effect of the embodiment.

FIG. 3 is a circuit diagram of a first specific example of the mixer and the attenuator according to the embodiment.

FIG. 4 is a circuit diagram of a second specific example of the mixer and the attenuator according to the embodiment.

FIG. 5 is a block diagram showing a configuration of a conventional receiving circuit.

FIG. 6 is a graph showing characteristics of a signal level detection circuit of a conventional receiving circuit.

[Explanation of symbols]

 2 antenna 4 RF amplifier 5 local signal 6 mixer 7 intermediate frequency signal 8 automatic gain control means 8a level detection circuit 8b control circuit 8c attenuator 9 voltage signal 10 IF filter (bandpass filter) 12 IF amplifier 14 signal level detection circuit 16 FM Detection circuit 17 Demodulation output 18 Addition means 19 Signal level detection output C1, C2 Capacitor

Claims (3)

[Claims] 1. A first amplifying means for amplifying a received signal, a mixer means for outputting an intermediate frequency signal from an output signal of the first amplifying means and a local signal, and an intermediate frequency filter for filtering the intermediate frequency signal. Second amplifying means for amplifying the output signal of the intermediate frequency filter, signal level detecting means for detecting the input signal level of the second amplifying means, and the signal level detecting means for detecting the input signal level of the intermediate frequency filter based on the output signal level of the intermediate frequency filter. Attenuating the signal level of either the output signal of the first amplifying means or the output signal of the mixer means so that the output of the intermediate frequency filter becomes a constant value when the level of the received signal exceeds a predetermined value. And an automatic gain control means for outputting a voltage signal according to the attenuation amount, and a voltage signal from the automatic gain control means and an output of the signal level detection means. Reception circuit characterized by comprising a, and adding smoothing means for smoothing San. 2. The automatic gain control means includes a level detection circuit for detecting the level of the output signal of the intermediate frequency filter, a smoothing circuit for smoothing the output of the level detection means, and a smoothing circuit for smoothing the output. A control circuit which outputs a control current based on the converted signal and outputs the voltage signal, and one of an output signal of the first amplifying means and an output signal of the mixer means based on the control current. The receiving circuit according to claim 1, further comprising an attenuating circuit that attenuates a signal level. 3. The receiving circuit according to claim 1, wherein the mixer means includes an attenuator circuit whose attenuation amount is variable.