JP2001217744A - Compound high frequency circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compound high frequency circuit miniaturized, facilitated in impedance matching between an antenna terminal and a transmitting terminal, reduced in the number of parts and capable of stable operation. SOLUTION: This circuit is provided with an antenna terminal ANT for connecting an antenna, transmitting terminal Tx for connecting a transmitting circuit, receiving terminal Rx for connecting a receiving circuit, first strip line SL1 connected between the receiving terminal Rx and the antenna terminal ANT, second diode connected between the strip line SL1 on the side of the receiving terminal Rx and the ground, and first diode D1 to be used as one part of components of a low-pass filter LPF1 connected between the antenna terminal ANT and the transmitting terminal Tx.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a composite high-frequency circuit in which a high-frequency switching circuit and a low-pass filter coexist.

[0002]

2. Description of the Related Art A composite high-frequency circuit in which a high-frequency switching circuit and a low-pass filter are combined is frequently used in a digital portable telephone terminal, for example, for switching between an antenna A, a transmitting circuit T and a receiving circuit T as shown in FIG. In the high-frequency switch unit SW used as
A low-pass filter LPF has been added between the high-frequency switch unit SW and the transmission circuit T in order to prevent harmonic components of the transmission signal Ftx generated in the transmission circuit T. For example, it is disclosed in JP-A-8-97743 and JP-A-9-200777.

FIG. 3 is an actual circuit diagram of a conventional composite high-frequency circuit. The symbol SW1 is a high frequency switch unit, LP
F indicates a low-pass filter unit. In the figure, ANT is an antenna terminal connected to the antenna A, Rx is a receiving terminal connected to the receiving circuit R,
Tx is a transmission terminal connected to the transmission circuit T. Here, the high-frequency switch unit SW1 includes a strip line L11,
L12, L13, diodes D11, D12 and capacitors C11, C12, C13, C14, C15, C16
Consists of

A low-pass filter section LPF is arranged between the high-frequency switch circuit section SW1 and the transmission circuit T, and includes strip lines L14 and L15 and capacitors C17, C18 and C19.

[0005]

However, the first diode D1 between the antenna terminal A and the transmission terminal Tx.
Is supplied by a bias voltage from the control terminal Vc1.
It is turned on and has a predetermined inductance component. Therefore, the high-frequency switch unit SW1 and the low-pass filter LP
An impedance mismatch occurs between F and it is necessary to match the impedance.

Further, with the downsizing of mobile communication devices such as mobile phones, further downsizing of electronic components is required. On the other hand, conventionally, a low-pass filter LPF
Since, for example, is composed of two strip lines L14 and L15 and three capacitors C17, C18 and C19, the number of components is greatly increased, and it has not been possible to sufficiently cope with miniaturization.

The present invention has been devised in view of the above problems, and has as its object to reduce the size of a first diode between an antenna terminal and a transmission terminal by using a switch element of a high-frequency switching circuit and a low-pass filter. It is an object of the present invention to provide a small composite high-frequency circuit that is easily used as a component and that can easily perform impedance matching.

[0008]

SUMMARY OF THE INVENTION The present invention has an antenna terminal to which an antenna is connected, a transmission terminal to which a transmission circuit is connected, and a reception terminal to which a reception circuit is connected. 1st placed between terminals
, A first strip line disposed between the receiving terminal and the antenna terminal, and a second diode connected between the receiving terminal side of the first strip line and ground. The diode is a complex high-frequency circuit characterized by being provided with a capacitor element at least on both ends and operating as a low-pass filter during a transmission operation.

According to the composite high-frequency circuit of the present invention, at the time of reception, the first and second diodes are turned off, and the reception signal input from the antenna terminal ANT is transmitted to the reception terminal Rx via the first strip line. Transmitted with little loss.

At the time of transmission, the first diode between the transmission terminal Tx and the antenna terminal ANT is turned on, and the transmission signal λ between the antenna terminal ANT and the reception terminal Rx is turned on.
The second diode between the first strip line and the ground is turned on for the first strip line having a line length of / 4.

Therefore, the antenna terminal ANT is connected to the reception terminal R
Since the x side looks like a short stub having a line length of λ / 4 of the transmission signal, the impedance is infinite at the frequency of the transmission signal and the x side is disconnected.

[0011] Also, the antenna terminal ANT to the transmission terminal Tx
On the side, a low-pass filter LPF is formed by the inductance component of the first diode in the ON state and the capacitor elements connected to both ends thereof. The low-pass filter is set to a frequency between the frequency of the transmission signal and a harmonic component operating as noise. As a result, the transmission signal is transmitted from the transmission terminal Tx to the antenna terminal AN.
The signal is transmitted to T, and the harmonic component of the transmission signal is hardly transmitted from the transmission terminal Tx to the antenna terminal ANT.

Therefore, the composite high-frequency circuit of the present invention has a function of switching between the antenna A, the transmission circuit T and the reception circuit T, and a function of blocking a harmonic component of a transmission signal generated in the transmission circuit T, and a configuration of the high-frequency switch unit SW1. The first element
Since the diode is also used as a component of a low-pass filter, impedance matching can be easily performed.
In addition, since the first diode, which is a component of the high-frequency switch unit SW1, is also used as a component of the low-pass filter, a unique low-pass filter LPF is not used, so that the entire circuit can be reduced in size.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A composite high-frequency circuit according to the present invention will be described below with reference to the drawings.

FIG. 1 shows a circuit diagram of an embodiment of a composite high-frequency circuit according to the present invention.

The composite high-frequency circuit includes a transmitting terminal Tx connected to the transmitting circuit T and an antenna terminal AN connected to the antenna A.
T and a receiving terminal Rx connected to the receiving circuit R.

The transmission terminal Rx is connected to the antenna terminal A.
A second strip line SL2 and a first diode D1 are arranged before reaching NT. A coil L1 and a capacitor C are arranged between the anode of the first diode D1 and the ground potential. The control terminal VC is connected between the coil L1 and the capacitor C4 via the resistor R1.

Also, the antenna terminal ANT is connected to the reception terminal R
Between x, the first strip line SL1 is arranged. Also, a second diode D2, between the receiving terminal side of the first strip line SL1 and the ground potential,
A capacitor C8 is provided. The cathode side of the second diode D2 is connected to the coil L2 via the coil L2.
2 are arranged.

A capacitor C1 is provided between the transmission terminal Tx and the second strip line SL2, between the connection point of the first diode D1 and the first strip line SL1 to the antenna terminal ANT. The capacitor C2 further includes an anode side of the second diode D2 and the receiving terminal R
x, a capacitor C3 is arranged.

The above-mentioned capacitors C1 to C5 are connected to the control signal (basis current) supplied from the control terminal Vc by the first signal.
, And a DC limiting coupling capacitor for supplying to the second diode D1 and the second diode D2. In particular, the capacitor C4 is a capacitor for removing high frequency noise from the control terminal Vc. The resistor R1 is a resistor for controlling the control current value to a predetermined value. The ill L1 is used to keep a high impedance between the second strip line and the control terminal Vc to prevent a transmission signal from being transmitted to the control terminal. Capacity.

Further, at the time of transmission, the coil L1
Is a high-frequency cut-off choke coil for maintaining the high impedance between the strip line SL2 and the control terminal Vc to prevent the transmission signal Ft from being transmitted to the control terminal Vc. It is a coil for preventing leakage.

Further, in the figure, a strip line SL2 is used to constitute a low-pass filter LPF1 on the transmission side.
A capacitor C5 is arranged between the transmission terminal Tx side end and the ground potential, and a capacitor C6 is arranged between the cathode side of the first diode D1 and the ground potential.

The low-pass filter LPF2 on the receiving side
In addition to the above-described capacitor C6, the first
A capacitor C7 is arranged between the receiving terminal Rx side end of the strip line SL1 and the ground potential.

In such a configuration, the first strip line SL1 has one wavelength with respect to the wavelength of the central frequency (simply called the transmission frequency Ftx) in the frequency band of the transmission signal Ft.
/ 4 line length.

At the time of reception, a negative reverse bias voltage or a control signal of 0 V is supplied to the control terminal Vc. Thus, the first diode D1 and the second diode D2 are turned off. That is, the first diode D
1 is off, the transmission terminal Tx and the antenna terminal AN
The connection between T will be cut. The second diode D
Since 2 is in the OFF state, the first strip line SL1 between the antenna terminal ANT and the receiving terminal Rx operates as a transmission line having a predetermined inductance component.

Further, the first of the predetermined inductance components
Third-order Chebychev π-type low-pass filter LPF2 by the strip line SL1 and the capacitors C6 and C7.
Is configured. The cutoff frequency of the low-pass filter LPF2 is mainly determined by the capacitance of the capacitors C6 and C7. This cutoff frequency is equal to the received signal Fr
Is set to a frequency higher than the reception frequency Frx in order to stably pass the central frequency (hereinafter simply referred to as the reception frequency Frx) of the frequency band of. For example, in the case of the GSM communication system (the reception frequency band is 925 to 960 MHz), for example, the frequency is 960 MHz or more, for example, 1 GHz. Thereby, the reception signal Fr is transmitted from the antenna terminal ANT to the reception terminal Rx with almost no loss. This allows
In the receiving circuit R connected to the receiving terminal Rx, frequency processing is simplified.

At the time of transmission, a positive voltage is supplied to the control terminal Vc. Thus, the first and second diodes D
1 and D2 are turned on when a bias current flows. Here, the first diode D1 and the second diode D2 are O
In the N state, it has an inductance component that cannot be ignored.

Then, the second diode D2 forms a series resonance circuit together with the capacitor C8 connected in series. Here, the first strip line SL1
Is set to １ ／ the length of the wavelength of the transmission frequency Ft, and the resonance frequency of the series resonance circuit including the second diode D2 and the capacitor C5 is set to the transmission frequency Ft. Have been. The coil L2 has a high inductance value so that the transmission signal hardly leaks to the ground via the coil L2.

Therefore, for the transmission frequency Ft, the impedance of the series resonance circuit becomes zero, and
Strip line SL1 operates as a short stub whose impedance becomes infinite with respect to the transmission signal,
The antenna terminal ANT and the receiving terminal Rx are disconnected.

Therefore, the transmission signal Ft can be stably derived to the antenna terminal ANT without leaking to the reception terminal Rx.

Here, the transmission terminal Tx and the antenna terminal AN
T, a second strip line SL2, a first diode D1 (having a predetermined inductance component) in an ON state, and a ground potential between both ends of both elements having both inductance components. Capacitor C5
And C6 are arranged.

That is, a third-order Chebychev π-type low-pass filter LPF1 is configured on the transmitting side. The cutoff frequency of this low-pass filter LPF1 is mainly
It is determined by the inductance component of the second strip line SL2 and the capacitance of the capacitors C5 and C6. Note that the capacitor C6 is determined based on the relationship with the above-described characteristics of the reception-side low-pass filter LPF2.

For example, the cut-off frequency of the low-pass filter LPF1 is set higher than the transmission frequency Ftx in order to allow the transmission frequency Ftx to pass stably. For example, the GSM communication method (when the transmission frequency band is 8
80-915 MHz), it is 915 MHz or more, for example, 1 GHz. Thus, the transmission signal Ft is transmitted from the transmission terminal Tx to the antenna terminal ANT with almost no loss. This eliminates the need for the filter section L separately from the high-frequency switch section SW1 as in the prior art.
The number of parts can be reduced. As a result, downsizing of the entire circuit can be achieved.

Further, in the present invention, the second harmonic and the third harmonic, which are harmonics of the transmission signal Ft generated in the transmission circuit T, can be blocked by the low-pass filter LPF1, the high-frequency noise can be reduced, and the stable communication can be achieved. Becomes possible.

Further, a low-pass filter LPF on the transmitting side
Since 1 is shared by a part of the high-frequency switching unit SW1, impedance matching between the transmission circuit T and the high-frequency switching circuit unit can be easily achieved.

In addition, the present invention includes the low-pass filter LPF2 on the receiving side. A transmission-side low-pass filter LPF1 and a reception-side low-pass filter LPF2;
Since the high-frequency switch section is configured to include the high-frequency switch section, harmonic components (noise) generated in the switch section can be suppressed not only at the time of transmission but also at the time of reception. Moreover, since the capacitor C6 is shared, the number of components can be minimized, and harmonic noise of transmission and reception can be reduced.

[0036]

EXAMPLE A composite high-frequency circuit according to the present invention was manufactured. As the first diode D1, a PIN diode which is about 1.5 nH in an on state is used. The circuit board has a board thickness of 0.
A dielectric material having a relative dielectric constant of 1 mm and a dielectric constant of 10 was used.

Here, a third-order Chebychev π-type low-pass filter using two capacitors has a cutoff frequency of 1
Assuming GHz, the capacitance value is 2.7 pF and the inductance value is 8.8 nH. Inductance value8.
A strip line length of about 13 mm is required to form 8 nH.

In the composite high-frequency circuit of the present invention, an inductance component is formed by combining the second strip line SL2 and the first diode D1. 7.3n
The line length may be equivalent to H, and under the above conditions, the line length may be about 11 mm.

Therefore, by using the composite high-frequency circuit of the present invention, the required size of the circuit board is 7.0 × 5.0 ×
The size was reduced from 1.0 mm to 6.5 × 5.0 × 1.0 mm.

[0040]

The composite high-frequency circuit according to the present invention shares a diode which is a component of the high-frequency switch as a component of the low-pass filter.

As a result, a high-frequency circuit can be obtained in which the number of components can be reduced, the size is small, the impedance matching between the antenna terminal and the transmission terminal can be easily achieved, and the insertion loss is small as compared with the related art.

Further, harmonic components (noise) of the transmission signal
, The stable switching operation can be achieved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a composite high-frequency circuit according to the present invention.

FIG. 2 is a block diagram of a conventional composite high-frequency circuit.

FIG. 3 is a circuit diagram of a conventional composite high-frequency circuit.

[Explanation of symbols]

ANT: Antenna terminal C1, C2, C3, C4, C5, C6, C7: Capacitor D1, D2: Diode L1, L2: Coil LPF1, LPF2: Low-pass filter R1: Resistor Rx: receiving terminal SL1, SL2: strip line Tx: transmitting terminal

Claims (1)

[Claims] An antenna terminal to which an antenna is connected, a transmission terminal to which a transmission circuit is connected, and a reception terminal to which a reception circuit is connected, and a terminal arranged between the transmission terminal and the antenna terminal. A first diode, a first strip line disposed between the reception terminal and the antenna terminal, and a second diode connected between the reception terminal side of the first strip line and ground. A composite high-frequency circuit characterized in that the first diode is provided with a capacitor element at least on both ends and operates as a low-pass filter during a transmission operation.