JP2525503Y2 - Direct conversion receiver - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct conversion receiver for demodulating a received modulated wave signal directly to a baseband signal, and more particularly, to miniaturization of the structure of a demodulation circuit.

[0002]

2. Description of the Related Art As one form of today's receiver, a receiver employing a direct conversion receiving system is known.

This receiver is called a direct conversion receiver, and generally has a configuration as shown in FIG.

[0004] In FIG.
The two received signals (FSK modulated waves and the like) are amplified to a predetermined level by the high-frequency amplifier 2 and branched and input to a pair of mixer circuits 5 and 6 at the subsequent stage.

A local oscillation signal having a frequency substantially equal to the carrier frequency of the received signal is supplied from the local oscillation circuit 3 to one of the mixer circuits 5 and 6, and a phase shift circuit 4 is applied to the other.
As a result, a local oscillation signal having a phase difference equivalent to π / 2 is input.

The demodulated signal waves of the respective output signals of the pair of mixer circuits 5 and 6 pass through low-pass filter sections (low-pass filters 7, 9 and 8, 10) to remove unnecessary frequency components. .

A detection circuit 11 is provided at a stage subsequent to the low-pass filter section, and compares two input signals respectively supplied from the pair of low-pass filter sections.
A demodulated signal is generated based on the comparison result.

[0008] As other components of the direct conversion receiver, reference numerals 12 and 13 denote power supplies for supplying power to the respective circuits.

As described above, in this type of direct conversion receiver, a mixer circuit (5, 6) is used in a received signal demodulation path. As an example of this mixer circuit, a base injection type as shown in FIG. It has been known.

However, in the base injection type mixer circuit, the local signal input from the local oscillation circuit 3 through the terminal 52 leaks to the terminal 51 to which the received signal is input, and the R
There is a risk of going around the part F.

To avoid this, a differential input type mixer circuit is often used today. In this case, the preceding stage of the mixer circuit has a configuration as shown in FIG.

In FIG. 5, reference numerals 5a and 6a denote differential input type mixer circuits, which are an RF signal input terminal 51, local signal input terminals 52a and 52b, output terminals 53a and 53a, respectively.
53b, an RF signal input terminal 61, local signal input terminals 62a and 62b, and output terminals 63a and 63b.

Further, a circuit (50) before the mixers 5a and 6a
a) is constituted by a local signal source 501, resistors R5 and R6, capacitors C4 and C5, transformers T1 and T2, and the like.

In such a circuit structure, since the differential input type mixers 5a and 6a use local signals as differential inputs, the phases thereof are opposite to each other, and the local signals inputted from the terminals 52a and 52b are canceled by each other. It is possible to reduce a phenomenon that a signal goes around the RF unit through the RF signal input terminal 51.

Here, the conventional circuit is designed to differentially input a local signal to the differential input type mixer circuits 5a and 6a.
The local signal from the local signal source 501 is
1, a circuit structure for converting to a differential input using T2 is adopted.

The transformers T1 and T2 have the characteristic of easily emitting signals, and radiation from a wiring pattern or the like can be considered in the vicinity of the transformers T1 and T2.
For example, from the local signal source 501, the transformers T1, T2
There is also a need to shield the region up to.

In order to meet such a demand for improvement, in the above-described conventional circuit structure using the transformers T1 and T2 in the preceding stage of the mixer circuit, the height of the parts where the transformers T1 and T2 are mounted is higher than other parts. In addition, the shielding becomes difficult, which hinders the miniaturization of the circuit structure.

[0018]

As described above, the conventional direct conversion receiver employs a pre-stage circuit including a transformer circuit to provide a differential input to a differential input type mixer circuit. The problem is that the shape of the transformer circuit is hampered, and the height of components at the time of mounting cannot be reduced uniformly. This makes it difficult to shield the circuit section and hinders miniaturization of the entire circuit structure. There was a point.

The present invention eliminates this problem and provides a circuit structure near the mixer circuit that is easy to shield and suitable for miniaturization.
An object of the present invention is to provide a direct conversion receiver that can contribute to miniaturization of the structure of the entire receiver.

[0020]

A direct conversion receiver according to the present invention includes a pair of mixer circuits for converting a reception frequency into two baseband signals having mutually different phases based on a differentially input local signal. And a mixer pre-stage circuit including a differential amplifier connected to a local signal input terminal of the mixer circuit and converting the local signal into a differential input of the mixer circuit.

[0021]

The direct conversion receiver of the present invention employs a pre-stage circuit section including a differential input amplifier in order to provide a differential input to a differential input type mixer circuit.

By using this differential input amplifier, the front-stage circuit section of the mixer circuit can be composed of only semiconductors, ICs, chip components, or the like, and the height of components at the time of mounting can be reduced uniformly. To facilitate the shield,
Thus, the entire circuit structure can be reduced in size.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a circuit diagram showing the configuration of a main part of a direct conversion receiver according to an embodiment of the present invention, and particularly corresponds to a former stage circuit portion of a mixer circuit in a demodulation circuit portion.

In FIG. 1 as well, components having the same functions as those of the conventional circuit portion shown in FIG. 5 are denoted by the same reference numerals.

Of the components of the circuit section shown in FIG. 1, the same components as those of the prior art include a differential input type mixer circuit 5a (I
ch) and 6a (Qch), respectively, and an RF signal input terminal 51, local signal input terminals 52a and 52b, output terminals 53a and 53b, and an RF signal input terminal 61, local signal input terminals 62a and 62b, and an output terminal 63a, respectively. 63b.

The detailed configuration of the mixer circuits 5a and 6a is as shown in the circuit diagram of FIG.
Q4 and Q5 and resistors R5, R6 and R7 are provided.
Here, the transistors Q3 and Q4 constitute a differential amplifier.

The differential input type mixers 5a and 6a having the above structure
On the other hand, in the present invention, the pre-stage circuit (50A) includes a local signal source 501, a constant current source 502, and impedance conversion buffers 503 to 506 (see FIG. 1).

In addition, transistors Q1 and Q2 forming a differential amplifier and resistors R1 to R4 are provided in the preceding circuit (50A).
And capacitors C1 to C3. Among them, in particular, two resistors R3 and R4 and two capacitors C
2 and C3 constitute a local signal phase shifter.
Next, the operation of this circuit will be described.

The local signal output from the local signal source 501 includes resistors R1, R2, transistors Q1, Q2
, A capacitor C1 and a constant current source 502.

The converted local signal is output as a differential output to buffers 503 and 5 for impedance conversion.
04, and further into the buffers 503 and 504
After each pass, the signal is divided into two signals.

One of the two divided local signals is supplied to a local signal input terminal 52 of the Ich mixer circuit 5a.
a and 52b.

Here, based on the local signal input from the input terminals 52a and 52b and the RF signal input from the RF signal input terminal 51, the mixer circuit 5a outputs a signal of the difference frequency component to an output terminal 53a. , 53b.

At the same time, the buffers 503, 5
The other local signal, which has been divided into two after passing through the signal line 04, undergoes phase shift control by a phase shifter comprising resistors R3 and R4 and capacitors C2 and C3.
After being subjected to impedance conversion by 5,506, it is input to local signal input terminals 62a, 62b of the Qch mixer circuit 6a.

The Qch mixer circuit 6a operates in the same manner as the Ich mixer circuit 5a, and the local signal input terminals 62a, 62a
2b and RF signal input terminal 6
Based on the RF signal input from No. 1, a signal of the frequency component of the difference is output to output terminals 63a and 63b.

According to the circuit of the present invention, a differential amplifier circuit for converting a local signal into a differential input, a phase shifter for shifting the phase of the local signal, a buffer for converting the impedance, and the like are provided. Each of them has a semiconductor, a resistor, a capacitor and the like as constituent elements, and can be made into an IC and a chip component.

Therefore, the height of the components when these components are mounted can be significantly reduced as compared with the case where a transformer circuit or the like is used, and the shielding of the circuit portion (in the dashed line portion in FIG. 1) is also helped. This is an extremely useful structure for miniaturizing a circuit.

[0038]

As described above, according to the direct conversion receiver of the present invention, the former stage using the differential amplifier circuit for converting the local signal given to the differential input type mixer circuit into the differential input. A circuit structure that can be used for ICs and chip components, including this differential amplifier circuit, phase shifters, and impedance conversion buffers, has been adopted, so the height of components during mounting is uniform. Lowering it makes the shielding easier, which can contribute to downsizing of the whole receiver.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a main configuration of a direct conversion receiver according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a detailed configuration of a mixer circuit in this type of direct conversion receiver.

FIG. 3 is a circuit diagram showing a general configuration of this type of direct conversion receiver.

FIG. 4 is a circuit diagram showing a configuration of a mixer circuit in this type of conventional direct conversion receiver.

FIG. 5 is a circuit diagram showing a main configuration of a conventional direct conversion receiver when the mixer circuit of FIG. 2 is used.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Antenna 2 High frequency amplifier 3 Local oscillator 4 Phase shift circuit 5, 5a, 5A mixer circuit (Ich) 6, 6a, 6A mixer circuit (Qch) 7, 8, 9, 10 Low-pass filter 11 Detection circuit 12, 13 Fixed Voltage power supply 51, 61 RF signal input terminal 52, 52a, 52b, 62a, 62b Local signal input terminal 53, 53a, 53b, 63a, 63b Mixer output terminal 50a, 50A Mixer pre-stage circuit 501 Local signal source 502 Constant current source 503 504, 505, 506 Impedance conversion buffer

Claims (4)

(57) [Scope of request for utility model registration] 1. A pair of mixer circuits for converting a reception frequency into two baseband signals having mutually different phases based on a differentially input local signal, connected to a local signal input terminal of the mixer circuit, A mixer pre-stage circuit including a differential amplifier for converting the local signal into a differential input of the mixer circuit. 2. A phase shifter for shifting the phase of a local signal after differential output is provided between a differential output of a differential amplifier circuit and one of local signal input terminals of the mixer circuit. The direct conversion receiver according to claim 1, wherein: 3. The direct conversion receiver according to claim 2, wherein the phase shifter comprises two resistors and two capacitors. 4. An impedance converter for impedance conversion between a differential output of a differential amplifier circuit and an input of a phase shifter and between an output of the phase shifter and one of local signal input terminals of the mixer circuit. 4. The direct conversion receiver according to claim 2, further comprising a buffer.