JP2002026752A - Receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a local oscillation signal from leaking to an LNA side to cause deterioration of the reception sensitivity and to prevent a DC offset from occurring between a demodulation output of an I signal and a demodulation output of a Q-signal, even when the receiver adopts the direct conversion system which directly demodulates a received RF signal, so that no DC offset is produced. SOLUTION: An isolator 4 is provided between the LNA 3 and multipliers 6A, 6B which configure a demodulation circuit. An inverse passing characteristic of the isolator 4 can prevent the local oscillation signal from being leaked to an output side of the LNA 3, so as to suppress deterioration in the sensitivity of a received signal and distortion in the LNA. Furthermore, the receiver is provided with a branching filter 5 which acts as a directional coupler, to distribute the signal from the LNA into two paths. The branching filter 5 can suppress leakage of the local oscillation signal from one multiplier 6A or 6B to the other multiplier 6B or 6A, thereby suppressing the occurrence of a DC offset of a base band signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving device suitable for use in, for example, a receiving circuit of a portable telephone terminal, and more particularly to a direct conversion type receiving device.

[0002]

2. Description of the Related Art Cellular phones and wireless LANs (Local Area Net)
work) etc., wireless data communication is drawing attention.
Conventionally, a receiving circuit of such a wireless communication device includes a receiving R
A superheterodyne method of demodulating a baseband signal after converting an F (high frequency) signal into an IF (intermediate frequency) signal is used.

FIG. 3 shows the configuration of a conventional superheterodyne receiving circuit.

[0004] In FIG.
The signal is transmitted to the LNA (Low Noise) through the duplexer 102.
e Amplifier) 103. Duplexer 10
Reference numeral 2 is for separating a transmission signal and a reception signal. L
At NA 103, the received RF signal is amplified.

The output of the LNA 103 is supplied to the multiplier 104 via the band pass filter 112. Multiplier 10
Reference numeral 4 functions as a mixing circuit for converting a received RF signal into an IF signal. The multiplier 104 includes a PLL (Phase Locked Loo).
p) VCO (Voltage Controlle) that constitutes the synthesizer
d Oscillator) 105 supplies a local oscillation signal.
The multiplier 104 multiplies the received RF signal by the local oscillation signal from the VCO 105.

When the frequency of the received RF signal is f _RX and the VCO
_Assuming that the frequency of the local oscillation signal from 105 is f _osc ,
A multiplier 104 are multiplied with the received RF signal and the local oscillation signal from the multiplier 104, and the signal of frequency (f _RX + f _osc), the signal of the frequency (f _RX -f _{os c)} is output .

[0007] The output of the multiplier 104 is supplied to a band-pass filter 106. The bandpass filter 106 extracts a signal of the frequency (f _RX −f _osc ) as a reception IF signal. Reception I from bandpass filter 106
The F signal is supplied to multipliers 107A and 107B.

The output of the oscillator 108 is supplied to the multiplier 107A. The output of the oscillator 108 is supplied to the multiplier 107B via the transfer unit 109.

The oscillator 108 outputs a local oscillation signal having the same frequency as the IF signal in order to demodulate the baseband signal from the received signal.

In the multiplier 107A, the received IF signal and the output of the oscillator 108 are multiplied. In the multiplier 107B, the received IF signal is multiplied by the output of the oscillator 108 shifted by π / 2 by the transfer unit 109. The I signal is demodulated by the multiplier 107A. The Q signal is demodulated by multiplier 107B.

The outputs of the multipliers 107A and 107B are output from output terminals 111A and 111B via low-pass filters 110A and 110B.

As described above, conventionally, a receiving circuit of a wireless communication device uses a superheterodyne method of demodulating a baseband signal after converting a received RF signal into an IF signal. However, the heterodyne method requires an IF circuit, and it is difficult to integrate the circuit.

Therefore, it is desired to reduce the size, weight, and cost by employing a direct conversion method for directly demodulating a baseband signal from a received RF signal. If the direct conversion method is adopted, IF
Since a circuit is eliminated and a large-capacity capacitor and an inductance for a low frequency are eliminated, an integrated circuit can be easily formed.

FIG. 4 shows a configuration in a case where the receiving circuit of the wireless communication device is a direct conversion.

In FIG. 4, a received RF signal from an antenna 201 is transmitted through a duplexer 202 to an LNA 203.
Supplied to In the LNA 203, the received RF signal is amplified. The output of LNA 203 is used as multipliers 204A and 204
B.

The output of the VCO 205 constituting the PLL synthesizer is supplied to the multiplier 204A. Multiplier 2
04B is supplied with the output of the VCO 205 via the transfer unit 206.

The VCO 205 outputs a local oscillation signal having the same frequency as the received RF signal in order to demodulate the baseband signal from the received signal.

The multiplier 204A uses the received RF signal and the VCO
205 is multiplied. In the multiplier 204B, the received RF signal and V shifted by π / 2 by the transfer unit 206 are output.
The output of the CO 205 is multiplied. The I signal is demodulated by the multiplier 204A. The Q signal is demodulated by multiplier 204B.

The outputs of the multipliers 204A and 204B are output from output terminals 208A and 208B via low-pass filters 207A and 207B.

[0020]

As described above, the direct conversion configuration eliminates the IF circuit, facilitates the integration of the circuit, and can reduce the size and weight.

However, when the direct conversion method is used, the frequency of the local transmission signal from the VCO 205 and the frequency of the received RF signal become the same, so that the arrow A
As shown by 11 and A12, a problem occurs that the local oscillation signal from the VCO 205 leaks to the LNA 203 side, causing deterioration of the receiving sensitivity.

As shown in FIG. 3, in the case of the superheterodyne system, the local oscillation frequency of the demodulation unit and the LNA
Since the received RF signal is different from the received RF signal of the demodulation unit 103, the provision of the bandpass filter can prevent the local oscillation signal of the demodulation unit from leaking into the LNA 103 side.

However, in the direct conversion method, since the frequency of the local transmission signal and the frequency of the received RF signal are the same, the multipliers 204A and 204B and L
Even if a bandpass filter is provided between the filter and the NA 203, no countermeasure is taken.

In such a configuration, the multiplier 204
A to multiplier 204B or multiplier 204B to multiplier 2
It is conceivable that the local oscillation signal leaks into each of the multipliers 204A and 204A.
04B is distorted, and even if the signal level is low, a DC (direct current) offset occurs between the baseband signals of the I signal and the Q signal.

Therefore, an object of the present invention is to provide a receiving RF
Even in the case of the direct conversion method in which the signal is directly demodulated, the local oscillation signal leaks to the LNA side, causing deterioration of the receiving sensitivity, or a DC offset between the demodulated output of the I signal and the demodulated output of the Q signal. It is an object of the present invention to provide a receiving device that does not occur.

[0026]

According to the present invention, there is provided means for amplifying a received signal, means for outputting a local oscillation signal having the same frequency as the received signal for demodulating a baseband signal from the received signal, A means for multiplying the amplified received signal by a local oscillation signal to demodulate a baseband signal; a direct conversion type receiving apparatus for directly demodulating the received signal and outputting a baseband signal; A receiving apparatus characterized in that an isolator is inserted between the means and the demodulation means.

According to the third aspect of the present invention, a duplexer for dividing the amplified received signal into two paths is further provided, and the received signal divided into two paths by the duplexer and two local sections having different phases from each other. The baseband signal of the I signal and the Q signal is demodulated by multiplying by the oscillation signal.

A multiplier 6A constituting a demodulation circuit with the LNA 3
And 6B are provided with an isolator 4. Thereby, even if the local oscillation signal from the VCO 7 leaks into the output side of the LNA 3, this signal is blocked by the reverse passing characteristic of the isolator 4. Therefore, it is possible to prevent the sensitivity of the received signal from deteriorating. Further, even if the level of the leakage signal of the local oscillation signal is high, distortion of the LNA can be suppressed.

Also, if such an isolator 4 is used, even if the load impedance seen from the isolator 4, that is, the input impedance of the duplexer 5 and the demodulation circuit changes, the reverse pass characteristic of the isolator 4 is sufficient. For example, the input impedance of the isolator 4 does not change. Therefore, the distortion characteristics of the LNA alone become the same as the characteristics when the LNA is incorporated as a device, and the design becomes easy.

Further, a splitter 5 of a directional coupler is provided to divide the signal from the LNA into two paths. The splitter 5 can suppress leakage of the local oscillation signal from one multiplier 6A or 6B to the other multiplier 6B or 6A. This allows the DC of the baseband signal
Offset can be suppressed.

[0031]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. This example is, for example, 2 GHz
Code Division Multiple Access using CDMA
The present invention is applied to a receiving circuit of a portable telephone system of the) type.

In FIG. 1, the reception RF from antenna 1
The signal is supplied to the LNA 3 via the duplexer 2. The duplexer 2 separates a transmission signal and a reception signal. The received RF signal from antenna 1 is LN
It is amplified at A3.

The output of the LNA 3 is supplied to the duplexer 5 via the isolator 4. The isolator 4 transmits a radio wave with almost no attenuation in one direction, and attenuates its power in the opposite direction.

As the isolator 4, for example, as shown in FIG. 2, one obtained by terminating one terminal 52C of a three-terminal circulator 51 of a ferrite circuit with a resistor 51 in a non-reflective manner is used. With such a configuration, radio waves are transmitted in only one direction between the terminal 52A and the terminal 52B.

The output of the isolator 4 is supplied to the duplexer 5. The RF signal sent from the LNA 3 via the isolator 4 is split by the splitter 5 into two paths. The output of the duplexer 5 is supplied to multipliers 6A and 6B.

The duplexer 5 is a directional coupler. When such a duplexer 5 is used, a signal is transmitted from an output terminal to an input terminal, or a signal is transmitted from one output terminal to the other output terminal. The signal will no longer be transmitted.

The duplexer 5 can be constituted by a circulator of a ferrite circuit. Further, it may be constituted by a differential circuit.

The output signal of the VCO 7 constituting the PLL synthesizer is supplied to the multiplier 6A. The output signal of the VCO 7 constituting the PLL synthesizer is supplied to the multiplier 6B after being shifted (π / 2) by the transfer unit 8.

The VCO 7 outputs a local oscillation signal having a frequency equal to the frequency of the received RF signal in order to directly demodulate the input RF signal into a baseband signal.

The input RF signal and the VCO are output by the multiplier 6A.
7 is multiplied by the output signal. Further, the input RF signal is multiplied by the output signal of the VCO 7 via the transfer unit 8 by the multiplier 6B. The I signal and the Q signal are demodulated by these multiplying circuits 6A and 6B. This multiplier 6A
And 6B are output from output terminals 10A and 10B via low-pass filters 9A and 9B, respectively.

As described above, the receiving circuit to which the present invention is applied is configured to directly demodulate the baseband signal by multiplying the received RF signal and the local oscillation signal by the multipliers 6A and 6B. ing. In this case, the received RF
Since the frequency f _RX of the signal is equal to the frequency f _lo of the local oscillation signal from the VCO 7, there is a concern that the local oscillation signal leaks into the LNA 3 and the sensitivity is degraded.

Therefore, in the embodiment of the present invention, LN
An isolator 4 is provided between A3 and the multipliers 6A and 6B. The isolator 4 prevents the local oscillation signal from leaking into the LNA 3 side.

That is, as shown by arrows A1 and A2 in FIG. 1, even if the local oscillation signal from the VCO 7 leaks into the output side of the LNA 3, this signal is blocked by the reverse passing characteristic of the isolator 4. . Therefore, it is possible to prevent the sensitivity of the received signal from deteriorating. Further, even if the level of the leakage signal of the local oscillation signal is high, distortion of the LNA can be suppressed.

Further, when such an isolator 4 is used, even if the load impedance viewed from the isolator 4, that is, the input impedance of the duplexer 5 and the demodulators (multipliers 6A and 6B) changes, the reverse passing of the isolator 4 can be performed. If the characteristics are sufficient, the input impedance of the isolator 4 does not change. For this reason, the distortion characteristics of the LNA alone become the same as the characteristics when the LNA is incorporated as a device, which facilitates the design.

In the embodiment of the present invention, a duplexer 5 of a directional coupler is provided. With this splitter 5,
The leakage of the local oscillation signal between the multiplier 6A and the multiplier 6B can be suppressed. Thereby, the DC offset of the baseband signal can be suppressed.

The present invention is applicable not only to the receiving circuit of a mobile phone terminal, but also to the receiving circuits of various devices that perform wireless data communication, such as a receiving circuit of a base station of a mobile phone and a receiving circuit of a wireless LAN. The same applies.

[0047]

According to the present invention, an isolator is provided between an LNA and a multiplier constituting a demodulation circuit. Thereby, even if the local oscillation signal leaks into the output side of the LNA, this signal is blocked by the reverse pass characteristic of the isolator. Therefore, it is possible to prevent the sensitivity of the received signal from deteriorating. Further, even if the level of the leakage signal of the local oscillation signal is high, distortion of the LNA can be suppressed.

Further, when such an isolator is used, even if the load impedance seen from the isolator, that is, the input impedance of the duplexer and the demodulation circuit changes, if the reverse pass characteristic of the isolator is sufficient, the isolator can be used. Since the input impedance does not change, the distortion characteristics of the LNA alone become the same as the characteristics when incorporated as a device. For this reason, design becomes easy.

Further, in the present invention, a splitter of a directional coupler is provided to divide the signal from the LNA into two paths. With this demultiplexer, leakage of the local oscillation signal into one multiplier and the other multiplier can be suppressed. Thereby, the DC offset of the baseband signal can be suppressed.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a block diagram of an example of an isolator.

FIG. 3 is a block diagram illustrating an example of a conventional superheterodyne receiving apparatus.

FIG. 4 is a block diagram of an example of a conventional direct conversion type receiving apparatus.

[Explanation of symbols]

3 LNA, 4 Isolator, 4 Duplexer, 6A, 6B Multiplier

Claims (4)

[Claims] A means for amplifying a received signal; a means for outputting a local oscillation signal having a frequency equal to the frequency of the received signal for demodulating a baseband signal from the received signal; A direct-conversion-type receiving apparatus that directly demodulates the received signal and outputs a baseband signal by multiplying a local oscillation signal and demodulating a baseband signal. A receiving device, wherein an isolator is inserted between the receiving device and the receiving device. 2. The receiving device according to claim 1, wherein said isolator is configured by terminating one end of a three-terminal circulator with no reflection. 3. A splitter for splitting the amplified received signal into two paths, wherein the splitter splits the received signal into two paths,
A receiving apparatus characterized in that a baseband signal of an I signal and a Q signal is demodulated by multiplying the two local oscillation signals having different phases from each other. 4. The receiving device according to claim 3, wherein said branching filter is a directional coupler.