JPH0615354U - Frequency selection circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] A frequency selection circuit that is inserted between a transmission / reception antenna of a transmission / reception system and a reception block to select the reception frequency band, attenuates the image interference frequency of the selected frequency, and reduces the effects of image interference. The purpose is to reduce. [Structure] The bandpass filter unit 1 has a capacitor C ₅ and a coil L ₄ connected in parallel between an input terminal T ₂ and an output terminal T _3, and a resonance circuit unit 3a having an antiresonance point at an image high frequency and a capacitor. C _3, and a capacitor C ₆ and the coil L ₅ in parallel, sequentially connected in series resonant circuit portion 3b having the anti-resonance point in the image interfering frequency, coil L ₃ between the ground and the input side of the resonant circuit 3a, Resonance circuit 3a, 3
The capacitors C ₂ and C ₄ are connected between the respective connection points of b and the capacitor C ₃ and the ground, and the coil L ₆ is connected between the output side of the resonance circuit 3b and the ground.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a frequency selection circuit, and more particularly to a frequency selection circuit inserted between a transmission / reception antenna and a reception block of a transmission / reception system to select a reception frequency band.

[0002]

[Prior art]

FIG. 4 shows a configuration diagram of a conventional example. The demultiplexing circuit 11 of the figure is applied to a transmission / reception system, and a transmission signal and a reception signal having different carrier frequencies (each carrier frequency is, for example, f ₀ = 931 MHz for a reception signal and f ₀ '= for a transmission signal). 886MHz) to prevent mutual interference, it is inserted at each connection point between the transmitting / receiving antenna and each transmitting block and receiving block. The terminal T ₁₂ is connected to the transmission / reception antenna, and the terminals T ₁₃ and T ₁₄ are connected to the reception flowchart and the transmission block, respectively.

The demultiplexing circuit 11 includes a capacitor C₁₁, Coil L₁₁, L₁₂And a bandpass filter 13 and 14. The branching circuit 11 has a terminal T₁₂, T₁₃ Frequency f between₀′ Signal has a high impedance and the frequency f₀Since the signal of '' acts so as not to pass, the frequency f input from the transmission block is ₀ 'Signals are prevented from entering the receiving block, and the terminal T₁₂, T₁₄Frequency f between₀Shows high impedance to the signal of frequency f₀Since it acts so as not to pass the signal of, the frequency f originally input to the reception block is₀The signal of is mixed into the transmission block is suppressed.

The bandpass filter 13 is composed of coils L _{13 to} L ₁₆ and capacitors C _{12 to} C ₁₄ , and is for extracting the signal of f ₀ from the signal input via the branching unit 12. The bandpass filter 14 is for extracting an RF (radio frequency) signal from the transmission signal input from the transmission block, and has a frequency characteristic as shown by the chain line in FIG.

[0005]

[Problems to be solved by the device]

However, the conventional frequency selection circuit has the characteristic that the gain peaks at the carrier frequency f ₀ of the received signal as shown by the alternate long and short dash line in FIG. 3, and the gain decreases and the attenuation increases as the distance from f ₀ increases. Therefore, sufficient attenuation cannot be performed at the image interference frequency f _{1 which} is a symmetrical frequency with respect to the center frequency f ₂ of the reception signal frequency f ₀ , and the reception block in the subsequent stage is adversely affected. There was a problem.

The present invention has been made in view of the above points, and provides a frequency selection circuit capable of reducing the influence of the interference signal frequency by increasing the attenuation amount at the interference signal frequency with a simple configuration. The purpose is to

[0007]

[Means for Solving the Problems]

 The present invention relates to a frequency selection circuit for selecting a reception signal having a predetermined carrier frequency from an input signal input from an input terminal, allowing the received signal to pass therethrough, and outputting the output signal from an output terminal in series with the input terminal and the output terminal. And a resonance circuit having a pass frequency band including the predetermined carrier frequency for passing the received signal and having an anti-resonance point at an interference frequency corresponding to the predetermined carrier frequency band. .

[0008]

[Action]

 Since the resonance circuit section has an anti-resonance point at the disturbing frequency, the attenuation amount can be maximized at the disturbing frequency in the frequency characteristics of the entire circuit, and the disturbing frequency component can be sufficiently attenuated and supplied to the next stage.

[0009]

【Example】

FIG. 1 shows a circuit diagram of an embodiment of the present invention. In the figure, 1 indicates a demultiplexing circuit. The demultiplexing circuit 1 includes a branching unit 2, a receiving side bandpass filter unit 3 serving as a frequency selection circuit, and a transmitting side bandpass filter 4 (the filter unit). Among them, the band-pass filter sections 3 and 4, each predetermined frequency _{f 0, f 0 '(931MHz} , 88 6MHz) the frequency band of the signal centered respectively (hereinafter, the signal of the f ₀ respectively, f _0' of It has a function of only the called signal) between the terminals T _2, T and between T ₂ of the _3, T ₄ passes, respectively. Further, the equivalent of the circuit between the branching unit 2, for example, a band-pass filter section 4 of the terminal T ₂ are when passing through a bandpass filter unit 3 thus a signal of f ₀ between terminals T _2, T _3, T ₃ Has a function to be substantially omitted. In the same way the bandpass filter unit 4 by the frequency f ₀ substantially signal bandpass filter unit 3 when passing between the terminals T _2, T ₄ from the circuit between terminals T _2, T ₄ of equivalently ' It has a function to be omitted.

The branching unit 2 includes a capacitor C ₁ that connects the terminal T ₂ and the ground, and coils L ₁ and L ₂ that connect the terminal T ₂ and the bandpass filter units 3 and 4, respectively. It In the case of this embodiment, the terminal T ₂ is connected to an antenna having a ground impedance of 50Ω, the capacitor C ₁ is 3 pF, and the coils L ₁ and L ₂ are 10 nH and 9.2 nH, respectively.

Further, in the bandpass filter unit 4, f ₂ is a resonance frequency in the circuit in which the bandpass filter unit 4 and the coil L ₂ of the branch unit 2 are connected.

The bandpass filter unit 3 includes a coil L ₃ that connects a connection point with the branch unit 2 and ground, and a coil L ₄ and a capacitor C ₅ from a connection point with the branch unit 2 to a terminal T _3. A resonance circuit section 3a in which a capacitor C ₃ , a coil L ₅ and a capacitor C ₆ are connected in parallel, and a resonance circuit section 3a in which the resonance circuit section 3a and a capacitor are connected in series. A common connection point with C ₃ , a common connection point between the capacitor C ₃ and the resonance circuit section 3b, and capacitors C ₂ and C ₄ , which connect between the ground and the terminal T _3, and the ground. Coil L ₆ for

The frequency characteristics of the circuits of the capacitors C ₅ and C ₆ and the coils L ₄ and L ₅ of the resonance circuit units 3a and 3b are the image resonance frequency f ₁ at the anti-resonance point as shown by the solid line in FIG. Is set.

Further, in the bandpass filter unit 3, the frequency f ₀ is the resonance frequency. The frequency characteristic of the bandpass filter unit 3 at this time is shown by a solid line in FIG. As shown by the solid line in FIG. 3, in the frequency characteristic of the bandpass filter unit 3, the gain peaks at the carrier frequency f ₀ of the received signal and the maximum attenuation occurs at the image frequency f ₁ . The attenuation amount is 20 to 30 dB larger than the conventional characteristic shown by the broken line in FIG.

Therefore, the signal of the image frequency f ₁ can be sufficiently attenuated, and the influence of the image frequency can be eliminated in the receiving section at the next stage.

Further, since the circuit configuration is simple, it is possible to reduce the image frequency component at low cost.

[0017]

[Effect of device]

 As described above, according to the present invention, since the attenuation amount can be set to be maximum at the frequency corresponding to the interference frequency of the selected frequency, the interference frequency can be surely attenuated and the selectivity can be improved. It has features such as improvement.

[Brief description of drawings]

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

FIG. 2 is a frequency characteristic diagram of a resonance circuit unit according to an embodiment of the present invention.

FIG. 3 is a frequency characteristic diagram of an embodiment of the present invention.

FIG. 4 is a configuration diagram of a conventional example.

[Explanation of symbols]

 1 demultiplexing circuit 2 branching unit 3 receiving side bandpass filter 3a, 3b resonant circuit unit 4 transmitting side bandpass filter

Claims (1)

[Scope of utility model registration request] 1. A frequency selection circuit for selecting a received signal having a predetermined carrier frequency from an input signal input from an input terminal, allowing the received signal to pass therethrough, and outputting the received signal from an output terminal in series between the input terminal and the output terminal. Connected to the
A frequency selection circuit comprising a resonance circuit section having a pass frequency band including the predetermined carrier frequency for passing the reception signal and having an anti-resonance point at an interference frequency corresponding to the predetermined carrier frequency.