JPH06303161A - If circuit - Google Patents

Abstract

PURPOSE:To reduce the number of components of a matching additional circuit between circuits required to receive an intermediate frequency broad band BPF and a narrow band BPF through switching by a mobile equipment of a cellular portable telephone system in which areas with a wide frequency channel interval and areas with narrow channel interval are in existence in mixture. CONSTITUTION:A simple auxiliary filter 8 of a board band BPF 6 and a notch filter is provided as a BPF for an intermediate frequency amplifier stage. In the case of receiving a broad band area signal, switches 7, 9 are thrown to the position of direct connection and to the position where an auxiliary filter 8 is connected in cascade in the case of narrow band signal reception.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to radios, and in particular
IF used in cellular phones of the type called cellular
It is about circuits.

[0002]

2. Description of the Related Art A cellular phone system called a cellular system has been put to practical use with a radio channel interval of 25 kHz.
After that, in response to the increase in demand, the frequency interval of the new method has become half (12.5 kHz) of the conventional method. Therefore, a mobile phone that moves in a mixed area of old and new systems is required to be used in both wideband and narrowband systems. FIG. 4 is a block diagram showing a configuration of a main part of a receiving unit of a conventional mobile phone. This configuration example is a two-stage superheterodyne type receiving circuit.
1 is a high frequency amplifier, 2 is a first mixer, 3 is a first intermediate frequency amplification stage (1stIF), 4 is a second mixer, and 1stIF
The output of 3 is converted into a second intermediate frequency signal by the output of the second local oscillator 5 and input to the second intermediate frequency amplification stage (2ndIF). In the 2ndIF, a wideband filter 13 and a narrowband filter 14 are arranged between the switch 7 and the switch 9. Reference numeral 10 is a 2nd IF amplifier, and 11 is a discriminator. Reference numerals 30, 31, 32, 33, 34, and 35 are additional circuits for impedance matching or the like. The mobile phone normally waits in the "wide band", and when receiving the "narrow band" signal from the base station side, the switch 7 and the switch 9 are operated by the band switching signal a to switch to the narrow band filter 14 side.

[0003]

In such a conventional circuit, since the filter blocks are connected in parallel, the narrow band filter 13 and the wide band filter 14 are provided with similar additional circuits 31, 32 and 33, 34, respectively. Must be used. Also, each filter must have similar required attenuation. In FIG. 5, the filters 13 'and 14' are connected in series in order to further obtain the out-of-band attenuation. From the above, the conventional method has a drawback that the number of parts is large and the cost of parts is high. An object of the present invention is to provide an IF circuit which can reduce the number of parts in order to solve the above-mentioned problems.

[0004]

The IF circuit of the present invention is cascade-connected to a mixer for converting to an intermediate frequency in an IF circuit of a radio device configured to receive by switching between wideband reception and narrowband reception. A wideband filter having wideband reception characteristics, a first switch cascade-connected to the wideband filter, and one terminal on an output side of the first switch, the wideband filter being connected to the first switch via the first switch. Auxiliary filter having such a characteristic that the overall characteristic is a desired narrow band reception when connected in cascade, a second switch to which the auxiliary filter is connected to one input terminal, and the other of the first switches. A predetermined additional circuit connected between the output terminal of the second switch and the other input terminal of the second switch, and the first switch and the second switch according to a switch switching signal. It is characterized in that the switch is configured to be switched the one terminal side or the other terminal side simultaneously.

[0005]

1 is a block diagram of a receiver showing an embodiment of the present invention. In the figure, 1 to 5 and 7, 9, 10, 1
1 is the same as the part of the conventional example of FIG. In the present invention, 2
After the nd mixer 4, the broadband filter 6, the switch 7, the auxiliary filter 8, and the switch 9 are added in this order in the additional circuits 20, 21,
22 and the other terminals of the switch 7 and the switch 9 are directly connected via an additional circuit 23. Electronic switches are used as the switches 7 and 9. When a "wideband" signal is given as the band switching signal a, the switch 7
Between the switch and the switch 9 is only the additional circuit 23, and the 2nd I
After F, it becomes "broadband". When a "narrow band" signal is given as the band switching signal a, the switches 7 and 9 are switched to the auxiliary filter 8 side, and the wide band filter 6 and the auxiliary filter 8 provide characteristics equivalent to those of the conventional narrow band filter. To be

When a narrow band filter characteristic is obtained by connecting the wide band filter 6 and the auxiliary filter 8 in cascade, the wide band filter 6 obtains the out-of-band attenuation amount, so that the auxiliary filter 8 has a simple notch for narrowing the band. It may be a filter having a configuration. When impedance cannot be achieved due to the impedances of the auxiliary filter 8 and the broadband filter 6, FIG.
As described above, the buffer amplifier 12 is added between the switch 7 and the auxiliary filter 8 to achieve matching. FIG. 2 is a characteristic diagram of the filter used in the present invention. FIG.
Is a characteristic of the auxiliary filter 8, and (C) is a total characteristic when the two filters are connected in cascade. From the above, when switching from "wideband" reception to "narrowband" reception, the wideband filter 6 and the auxiliary filter 8
Since it has a cascade connection structure and narrow band reception is possible, it is possible to reduce the number of additional circuits. Further, when it is desired to obtain the out-of-band attenuation amount, the attenuation amount can be obtained by adding the filter 6 ′ as shown in FIG. 3, so that it is cheaper than before and the number of parts can be reduced.

[0007]

As a result of implementing the present invention, the number of parts is reduced and the cost and size are greatly reduced as compared with the conventional method.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram of filter characteristics according to the present invention.

FIG. 3 is a diagram of another embodiment of the present invention.

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

FIG. 5 is a diagram illustrating a conventional configuration example.

[Explanation of symbols]

 1 High Frequency Amplifier 2 1st Mixer 3 1stIF 4 2nd Mixer 5 2nd Local Oscillator 6,6 'Wideband Filter 7 Switch A 8 Auxiliary Filter 9 Switch B 10 2ndIF Amplifier 11 Discriminator 12 Buffer Amplifier 13, 13' Broadband Filter 14 , 14 'Narrow band filter 20, 21, 22, 23, 24 Additional circuit 30, 31, 32, 33, 34, 35 Additional circuit

Claims (1)

[Claims] 1. A wideband filter having a wideband reception characteristic cascade-connected to a mixer for converting to an intermediate frequency in an IF circuit of a radio device configured to switch between wideband reception and narrowband reception, and the wideband. A first switch connected in cascade to the filter and one terminal on the output side of the first switch connected to the wide band filter via the first switch, and a desired overall characteristic is obtained. Auxiliary filter having characteristics for narrow band reception, a second switch having the auxiliary filter connected to one input terminal, the other output terminal of the first switch, and the other of the second switches A predetermined additional circuit connected between the first terminal and the second switch at the same time according to a switch switching signal. Side or the other terminal side is configured to be switched to the IF circuit.