JPH1198043A - Frequency conversion circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a calling with satisfactory transmission quality between different radio service areas and further even in the place different in radio wave state within the same radio service area. SOLUTION: This circuit is provided with a local signal level adjusting part 3 and a receiving electric field strength recognizing part 5 and an AMP-AGC 19 controls the size of an intermediate frequency signal Vif according to the size of a level of an input signal. The part 5 detects an operation of a the AMP-AGC 19, changes a voltage level of control voltage Vc and changes forward conductive resistance value of a PIN diode that constitutes the part 3. As a result of that, the size of a local signal V0 is changed and its ratio to an input signal level becomes appropriate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a frequency conversion circuit provided inside a mobile station of a mobile communication system.

[0002]

2. Description of the Related Art In recent years, with the development of telecommunication technology, various types of information communication systems have appeared and have been widely spread. A mobile communication system can be cited as one of those which has been rapidly spreading. In particular, the spread of mobile phones is noteworthy. With the spread,
The number of mobile stations within a wireless service area covered by one base station is steadily increasing. As a result, there is a growing demand for mobile stations to improve transmission and reception performance.

[0003]

However, the conventional mobile station as described above has the following problems to be solved. One of the important factors that determine the transmission / reception performance of a mobile station is various characteristics of a frequency conversion circuit provided in the mobile station. Among these characteristics, particularly important characteristics are a waveform distortion characteristic and an S / N ratio characteristic. Here, the S / N ratio refers to the ratio between the signal level and the noise level. These two characteristics show a slight deviation between different wireless service areas and even within the same wireless service area due to radio wave conditions in the area. However, conventional mobile stations do not have effective means for responding to this change.

[0004]

The present invention adopts the following constitution in order to solve the above points. <Configuration 1> A mixer that receives an input signal and a local oscillation signal and performs frequency conversion to obtain a desired intermediate frequency output, and receives an antenna input signal based on the magnitude of the intermediate frequency output output from the mixer. A received electric field strength recognition unit that recognizes the magnitude of the electric field strength and outputs a control voltage correlated to the magnitude, and a control voltage output from the received electric field strength recognition unit, and a level of a local oscillation signal applied to the mixer. The local oscillator signal level adjuster controls the level of the local oscillator signal to be applied to the mixer when the antenna input signal is small, and the local antenna signal is large when the antenna input signal is small. A frequency conversion circuit operable to increase the level of the local oscillation signal applied to the mixer.

<Structure 2> In the circuit described in Structure 1,
The local oscillation signal level adjusting unit is configured by a PIN diode connected to the load side of the local oscillation signal, applies a control voltage output by the reception electric field strength recognition unit in the forward direction of the PIN diode, and PI depending on the size
A frequency conversion circuit for changing a level of a local signal applied to a mixer by changing a forward conduction resistance of an N diode.

<Structure 3> In structure 1, the local oscillation signal level adjusting section is constituted by a variable amplifier which amplifies the local oscillation signal and inputs the amplified signal to the mixer.
A frequency conversion circuit, wherein the level is changed by a control voltage output by a reception field strength recognition unit to change the level of a local signal applied to the mixer.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the illustrated embodiments. FIG. 1 is a block diagram of a frequency conversion circuit according to the first embodiment. Before explaining FIG. 1, in order to facilitate understanding of the present invention, first, an outline of an entire configuration of a receiving circuit of a mobile phone will be described, mainly around a frequency conversion circuit.

FIG. 2 is a block diagram of a receiving circuit of a mobile phone. 2, the receiving circuit of the mobile phone includes an antenna 11, a matching unit 12, a DU
P13, AMP-B14, RBPF15, frequency conversion circuit 16, AMP-C17, IFBPF18, AMP-A
It has a GC 19, an AMP-D 20, and a demodulator 21. The antenna 11 is a part that receives an 880 MHz band electromagnetic wave. The matching unit 12 is a part that performs impedance matching between the antenna 11 and a subsequent circuit system.

A DUP (Duplexer) 13 is a filter for separating a transmission signal and a reception signal so that the transmission circuit and the reception circuit share the antenna 11. It is commonly called a duplexer. The AMP-B14 is a high-frequency broadband amplifier that amplifies the high-frequency signal received by the antenna 11 as it is. RBPF (R-Band-Pass-Filter) 15 is an AM
The wideband signal amplified by P-B14 is converted from 869 MHz to
This is a bandpass filter that passes a signal having a pass band of 25 MHz up to 894 MHz.

The frequency conversion circuit 16 mixes the input signal V1 of the frequency F1 passing through the RBPF 15 with the local signal V0 of the frequency F2 oscillated by a local oscillator provided in the receiver, and outputs an intermediate frequency signal Vif. I do. The frequency becomes Fif = | F1-F2 |. This Fif is generally called an intermediate frequency. In order to fulfill this function, MIX1, VCO2, and AMP-A4 are provided. MI
X1 is a so-called mixer, which is a mixer that mixes the two signals. VCO2 is a local oscillator that oscillates at the frequency F2. AMP-A4 is an amplifier that amplifies the output oscillated by VCO2 and adds it to MIX1 as local oscillation signal V0, and has a fixed amplification factor.

Next, problems of the frequency conversion circuit 16 will be described with reference to the drawings. FIG. 3 is a signal waveform diagram of each part of the frequency conversion circuit. The horizontal axis represents time, and the vertical axis represents signal level. (A) shows the input signal V1 (FIG. 2). (B) represents the local oscillation signal V0 (FIG. 2).
(C) shows a mixture of the input signal V1 and the local oscillation signal V0.
The composite signal inside MIX1 (FIG. 2) is shown. (D)
Represents an intermediate frequency signal Vif (FIG. 2) which is an output signal of the frequency conversion circuit 16 (FIG. 2). The diagram described above shows the state of the frequency conversion circuit 16 at the time of standard operation.

On the other hand, the input signal V1 shown in (a) is different between radio service areas or within the same area, and the level of the input signal V1, the maximum value Vmax, the minimum value Vmin, etc. are changed depending on the radio wave condition. Will be very different.
(E) shows a case where the input signal V1 has become too small. At this time, the S / N of the intermediate frequency signal Vif deteriorates. (F) shows a case where the input signal V1 has become too large. At this time, the waveform distortion of the intermediate frequency signal Vif increases due to the saturation of the leading end of the signal waveform.

As a result, when the input signal V1 is an analog modulation signal, it immediately affects the noise and sound quality of the audio output. Further, even when the input signal V1 is a digital modulation signal, the error rate of the demodulated signal increases. The effect is slightly reduced as compared with the case of the analog modulation signal, but the effect cannot be ignored. The description of the configuration and problems of the frequency conversion circuit 16 has been completed, and the description returns to FIG.

AMP-C17 and IFBPF (IF-Band-
The Pass-Filter 18 converts the intermediate frequency signal Vif output from the frequency conversion circuit 16 into a center frequency of 85 MHz and -3 dB.
It is a part that amplifies in an intermediate frequency band of a pass band of 1.5 MHz. AMP-C17 is an amplifier, and IFBPF18 is a bandpass filter of the above-mentioned band. AMP-AGC
An amplifier 19 controls the gain of the selectively amplified intermediate frequency signal Vif output from the IFBPF 18 to a certain level. Here, it is assumed that the level of the input signal V1 is too small. As a result, the intermediate frequency signal Vi
Since f also becomes small, it is necessary to amplify to a certain level by the AMP-AGC19.

It is also assumed that the level of the input signal V1 is too high. As a result, the intermediate frequency signal Vif also increases, so that the AMP-AGC 19 needs to attenuate it to a certain level. The demodulator 21 has an AMP-AG
This is a demodulator for demodulating the output of C19 into a voice signal or a data signal. As described above, the outline of the receiving circuit configuration of the mobile phone has been described mainly with respect to the frequency conversion circuit 16.
Returning to the description, the frequency conversion circuit according to the first specific example will be described.

<Configuration of Specific Example 1> As shown in FIG. 1, the frequency conversion circuit according to the specific example 1 includes a MIX1, a VCO 2, a local oscillation signal level adjuster 3, an AMP-A4, and a received electric field strength recognizer 5. Is provided. MIX1 is the input signal V of the frequency F1 as already described in the receiving circuit configuration of the mobile phone.
1. The frequency F at which the local oscillator in the receiver oscillates
2 and the intermediate frequency signal Vi.
This is the part that outputs f. The frequency is Fif = | F
1−F2 |.

VCO2 is a local oscillator oscillating at a frequency F2. It is called a voltage controlled oscillator, and usually uses a variable capacitance diode as a resonance capacitance. The oscillation capacitance is changed by changing the resonance capacity according to the magnitude of the DC reverse bias applied to the variable capacitance diode. The local oscillation signal level adjustment unit 3 is a unit that changes the magnitude of the local oscillation signal V0 input to the MIX1. PIN
A diode was used. The PIN diode is a diode in which high-frequency characteristics are improved by inserting a low-concentration insulating layer I between a high-impurity-concentration P-type region and an N-type region. Further, when the control voltage Vc is applied in the forward direction and the voltage level is increased, the forward conduction resistance is reduced.

The reception electric field strength recognition section 5 is an AMP-AGC
19, the amplification and attenuation operations are detected, and the magnitude of the received electric field strength that is correlated with the input signal V1 is recognized. The AMP-AGC 19 increases the level of the control voltage Vc when increasing the amplification factor, and decreases the level of the control voltage Vc when decreasing the amplification factor. As described above, the amplification and attenuation operations of the AMP-AGC 19 are variable amplifiers that increase the amplification factor when the intermediate frequency signal Vif is too small, and decrease the amplification factor when the intermediate frequency signal Vif is too large. AMP-A4
Is an amplifier that amplifies the local oscillation signal V0 of the frequency F2 output from the VCO 2 to a certain level.

<Operation of Embodiment 1> FIG. 4 is a diagram for explaining the level adjustment of the local oscillation signal. (A) is a case where the input signal is too small. In this state, the level of the local oscillation signal V0 is set to V
When it is fixed at 00, the input signal is too small, and as a result, the local signal is too large relative to the input signal. (B) is a case where the local oscillation signal is reduced. This state shows a state in which the magnitude of the local oscillation signal V0 is reduced to V01, and the ratio of the magnitude of the local oscillation signal to the magnitude of the input signal is made appropriate.

(C) is a case where the input signal is too large. This state indicates that when the magnitude of the local oscillation signal V0 is fixed to V00, the level of the input signal is too large, and as a result, the local oscillation signal is too small relative to the input signal. (D) is a case where the level of the local oscillation signal is increased. This state indicates a state in which the level of the local oscillation signal V0 is increased to V02, and the ratio of the magnitude of the local oscillation signal to that of the input signal is adjusted appropriately.

It is assumed that the user carrying the portable telephone switches on and receives an incoming call signal. MIX1 starts frequency conversion using the incoming call signal as input signal V1. It is now assumed that the level of the input signal is too low and the state of FIG. This state is a state in which the S / N of the intermediate frequency signal Vif is deteriorated, as described above. At this time, as described above, the AMP-AGC 19 attempts to amplify the intermediate frequency signal Vif to a certain level because the intermediate frequency signal Vif is too small. The reception field strength recognition unit 5 detects this operation, increases the voltage level of the control voltage Vc, and reduces the forward conduction resistance of the PIN diode constituting the local signal level adjustment unit 3. As a result, the local oscillation signal V0 becomes small, and the ratio to the input signal level becomes appropriate. The state is (b).

Next, it is assumed that the input signal is too large and is in the state (c). This state is a state where the waveform distortion of the intermediate frequency signal Vif increases as described above. At this time, as described above, the AMP-AGC 19 attempts to lower the amplification factor in order to reduce the intermediate frequency signal Vif to a certain level because the intermediate frequency signal Vif is too large. The reception electric field strength recognition section 5 detects this operation and outputs the control voltage V
The voltage level of c is reduced. When the voltage level of the control voltage Vc decreases, the forward conduction resistance value of the PIN diode constituting the local oscillation signal level adjustment unit 3 increases. As a result, the local oscillation signal becomes large and the ratio to the input signal level becomes appropriate. The state is (d).

As described above, in the frequency conversion circuit according to the first embodiment, the control loop Lc is formed by the MIX 1, the reception electric field strength recognition unit 5, and the local oscillation signal level adjustment unit 3.
Here, the reception electric field strength recognition unit 5 determines that the AMP-AGC 19
Is described, the control loop Lc is not limited to this configuration. The output of the demodulator 21 (FIG. 2) or a received electric field strength recognition signal formed therein may be used. Further, at times, the control loop Lc may be cut in the middle to manually change the control voltage Vc. In this case, it is not necessary to configure the local oscillation signal level adjustment unit 3 with a PIN diode, and a manual variable resistor may be used.

<Effect of Specific Example 1> The frequency conversion circuit according to the present invention has the following effects by including the local oscillation signal level adjustment unit 3 and the reception electric field strength recognition unit 5. 1. Different radio service areas, and even in the same radio service area with different radio wave conditions,
Calls with good transmission quality are now possible. 2. Since the change characteristic of the forward conduction resistance value of the PIN diode is used as the local signal level adjuster 3, the local signal level adjuster 3 having a simple configuration and good high frequency characteristics can be obtained. Calls with good transmission quality are now possible with minimal cost increase.

<Structure of Embodiment 2> FIG. 5 is a block diagram of a frequency conversion circuit according to Embodiment 2. Only the differences from the specific example 1 will be described. The reception field strength recognition unit 5
The amplification and attenuation operations of the P-AGC 19 are detected, and the magnitude of the received electric field strength correlated with the input signal V1 is recognized. This is a portion for outputting the control voltage Vc correlated to the magnitude. This control voltage Vc is applied to the local oscillation signal level adjuster 6,
This is a portion for controlling the amplification degree and changing the local oscillation signal V0.

The local oscillation signal level adjusting unit 6 is provided with the signal A of the first embodiment.
This is a variable amplifier configured to change the amplification factor of MP-A4 (FIG. 1) according to the level of the control voltage Vc. When the level of the control voltage Vc output by the reception electric field strength recognition unit 5 increases, the amplification factor is reduced, and when the level of the control voltage Vc decreases, the amplification factor is increased and the signal is input to the MIX1. This is a portion for changing the size of the signal V0. The frequency conversion circuit according to the second example having the above configuration operates as follows.

<Operation of Specific Example 2> MIX1 and AMP-A
The reception electric field strength recognition section 5 including the GC 19 and the local oscillation signal level adjustment section 6 form a control loop Lc. It is now assumed that the input signal is too small and is in the state shown in FIG. At this time, as described above, the AMP-AGC 19 attempts to amplify the intermediate frequency signal Vif to a certain level because the intermediate frequency signal Vif is too small. Reception electric field strength recognition unit 5
Detects this operation and increases the voltage level of the control voltage Vc. As a result, the amplification factor of the local oscillation signal level adjusting unit 6 is reduced to make the ratio between the level of the local oscillation signal and the level of the input signal appropriate (FIG. 4B).

Similarly, it is assumed that the level of the input signal is too large and the state shown in FIG. At this time, as described above, the AMP-AGC 19 tries to reduce the amplification factor because the intermediate frequency signal Vif is too large. The reception field strength recognition unit 5 detects this operation,
The voltage level of the control voltage Vc is reduced. As a result, the amplification factor of the local oscillation signal level adjustment unit 6 is increased to make the ratio of the level of the local oscillation signal to the level of the input signal appropriate (FIG. 4).
(D)).

<Effect of Specific Example 2> The frequency conversion circuit according to the specific example 2 includes the local oscillation signal level adjusting unit 3 constituted by a variable amplifier, thereby adding to the effect of the specific example 1 and further simpler. With the configuration, it is possible to obtain the local oscillation signal level adjuster 6 having good high frequency characteristics.

[Brief description of the drawings]

FIG. 1 is a block diagram of a frequency conversion circuit according to a specific example 1.

FIG. 2 is a block diagram of a receiving circuit of the mobile phone.

FIG. 3 is a signal waveform diagram of each part of the frequency conversion circuit.

FIG. 4 is an explanatory diagram of level adjustment of a local oscillation signal.

FIG. 5 is a block diagram of a frequency conversion circuit according to a specific example 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 MIX 2 VCO 3 Local signal level adjustment part 4 AMP-A 5 Reception electric field strength recognition part 19 AMP-AGC

Claims (3)

[Claims] 1. A mixer that receives an input signal and a local signal and performs frequency conversion to obtain a desired intermediate frequency output, and a mixer that outputs a desired intermediate frequency output based on the magnitude of the intermediate frequency output output from the mixer.
A reception field strength recognition unit that recognizes the magnitude of the reception field strength of the antenna input signal and outputs a control voltage correlated to the magnitude, and a control voltage output by the reception field strength recognition unit,
A local oscillation signal level adjusting unit for controlling a level of the local oscillation signal applied to the mixer; wherein the local oscillation signal level adjusting unit, when the antenna input signal is small, the level of the local oscillation signal applied to the mixer The frequency conversion circuit operates to increase the level of a local oscillation signal applied to the mixer when the antenna input signal is large. 2. The circuit according to claim 1, wherein the local signal level adjuster is constituted by a PIN diode connected to a load side of the local signal, and the reception electric field strength is recognized in a forward direction of the PIN diode. A frequency conversion circuit for applying a control voltage output by the unit, changing the forward conduction resistance of the PIN diode according to the magnitude of the control voltage, and changing the level of a local signal applied to the mixer. . 3. The local oscillator signal level adjusting unit according to claim 1, wherein the local oscillator signal level adjusting unit is configured by a variable amplifier that amplifies the local oscillator signal and inputs the amplified signal to a mixer. A frequency conversion circuit characterized by changing a level of a local oscillation signal applied to a mixer by changing the level by a control voltage to be output.