JPH11234161A - Switching circuit - Google Patents
Switching circuitInfo
- Publication number
- JPH11234161A JPH11234161A JP3614398A JP3614398A JPH11234161A JP H11234161 A JPH11234161 A JP H11234161A JP 3614398 A JP3614398 A JP 3614398A JP 3614398 A JP3614398 A JP 3614398A JP H11234161 A JPH11234161 A JP H11234161A
- Authority
- JP
- Japan
- Prior art keywords
- signal
- circuit
- differential amplifier
- gain
- amplifier circuit
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
Landscapes
- Superheterodyne Receivers (AREA)
- Noise Elimination (AREA)
- Circuits Of Receivers In General (AREA)
Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、ラジオ受信機にお
けるＩＦ信号の切り換えに用いられる切換回路に関す
る。The present invention relates to a switching circuit used for switching an IF signal in a radio receiver.
【０００２】[0002]
【従来の技術】一般に、ラジオ受信機において、ＦＭ受
信回路と、影像妨害が除去することができるダブルコン
バージョン式のＡＭラジオ受信回路とが同一半導体基板
上に1チップ化されている。このようなラジオ受信回路
は図３のように構成される。図4において、ＦＭ受信
時、ＦＭＲＦ信号はＦＭ−ＲＦ同調増幅回路１で同調及
び増幅された後、混合回路２のＦＭ混合部３で局部発振
信号により中心周波数１０．７ＭHzのＦＭＩＦ信号に周
波数変換される。ＦＭＩＦ信号は共通フィルタ４で帯域
制限された後、バッファ回路５及び切換回路６を介して
ＦＭフィルタ７に印加され、帯域制限された後ＦＭ検波
回路８でＦＭ検波される。2. Description of the Related Art In general, in a radio receiver, an FM receiving circuit and a double-conversion AM radio receiving circuit capable of removing image interference are integrated into one chip on the same semiconductor substrate. Such a radio receiving circuit is configured as shown in FIG. In FIG. 4, at the time of FM reception, an FMRF signal is tuned and amplified by an FM-RF tuning amplifier circuit 1, and then frequency-converted into an FMIF signal having a center frequency of 10.7 MHz by a local oscillation signal in an FM mixing unit 3 of a mixing circuit 2. Is done. The FMIF signal is band-limited by the common filter 4, applied to the FM filter 7 via the buffer circuit 5 and the switching circuit 6, band-limited, and FM-detected by the FM detection circuit 8.
【０００３】また、ＡＭ受信時、ＡＭＲＦ信号はＡＭ−
ＲＦ同調増幅回路９で増幅された後、ＡＭ混合部１０で
第１ＡＭＩＦ信号に周波数変換される。第１ＡＭＩＦ
は、共通フィルタ４、バッファ回路５、切換回路６を介
して、第１ＡＭフィルタ１１で帯域制限され、その後第
２のＡＭ混合回路１２で第２ＩＦ信号に周波数変換さ
れ、さらにＡＭ検波回路１３でＡＭ検波される。ところ
で、混合回路２はＦＭ及びＡＭ用のダブル差動増幅回路
をそれぞれ有し、ＦＭ及びＡＭＲＦ信号がそれぞれのダ
ブル差動増幅回路に印加され、各々のＩＦ信号が共通出
力端から出力される。ＡＭ受信回路にダブルコンバージ
ョン方式が採用されており、第１ＡＭＩＦ信号のＩＦ周
波数としてＦＭＩＦ信号のＩＦ周波数と同一であるので
混合回路２の出力端を共通化できる。この共通出力端か
ら発生するＦＭ及びＡＭＩＦ信号は受信バンドに応じて
切換回路６で分岐され、それぞれＦＭ及びＡＭ検波回路
８及び１３に印加される。At the time of AM reception, the AMRF signal is
After being amplified by the RF tuning amplifier circuit 9, the frequency is converted into a first AMIF signal by the AM mixer 10. 1st AMIF
Is band-limited by a first AM filter 11 via a common filter 4, a buffer circuit 5, and a switching circuit 6, then is frequency-converted to a second IF signal by a second AM mixing circuit 12, and is further amplified by an AM detection circuit 13. It is detected. The mixing circuit 2 has double differential amplifying circuits for FM and AM, respectively. The FM and AMRF signals are applied to the respective double differential amplifying circuits, and the respective IF signals are output from a common output terminal. Since the double conversion method is adopted for the AM receiving circuit and the IF frequency of the first AMIF signal is the same as the IF frequency of the FMIF signal, the output terminal of the mixing circuit 2 can be shared. The FM and AMIF signals generated from the common output terminal are branched by the switching circuit 6 according to the reception band, and applied to the FM and AM detection circuits 8 and 13, respectively.
【０００４】[0004]
【発明が解決しようとする課題】ＦＭ受信では、希望局
に隣接して強電界の妨害局が存在する場合妨害局の電波
がＦＭラジオ受信系統に飛び込み希望局が妨害局によっ
て妨害を受ける隣接妨害が発生することがある。これを
防止する対策として、ＦＭ用のＩＦフィルタとして広帯
域及び狭帯域の２つのフィルタを用意し、隣接妨害が発
生するとＦＭＩＦ信号の帯域をより狭く帯域制限して妨
害局を除去するようにしていた。しかしながら、この対
策を図４の従来のラジオ受信機に施そうとすると、ＦＭ
受信系統にさらにフィルタを設けることになり、回路が
増えるだけでなく、ＦＭＩＦ信号自体やＡＭ／ＦＭＩＦ
信号の切り換えなどの回路が複雑化するという問題があ
った。特に、ＦＭＩＦ信号自体やＡＭ／ＦＭＩＦ信号の
切り換えに際して、ラジオ受信回路全体のゲインがＡＭ
受信系統や、広帯域及び狭帯域のＦＭ受信系統によって
それぞれ異なるので、ゲインの調整も必要になり、さら
に回路が複雑化するという問題があった。In FM reception, when there is a jamming station of a strong electric field adjacent to the desired station, the radio wave of the jamming station jumps into the FM radio receiving system and the desired station is jammed by the jamming station. May occur. As a measure to prevent this, two filters of a wide band and a narrow band are prepared as IF filters for FM, and when adjacent interference occurs, the band of the FMIF signal is band-limited more narrowly to remove the interfering station. . However, when this measure is applied to the conventional radio receiver shown in FIG.
Since a filter is further provided in the receiving system, not only the number of circuits increases, but also the FMIF signal itself and the AM / FMIF
There has been a problem that circuits for switching signals are complicated. In particular, when the FMIF signal itself or the AM / FMIF signal is switched, the gain of the entire radio receiving circuit is set to AM
Since it differs depending on the receiving system and the broadband and narrowband FM receiving systems, it is necessary to adjust the gain and the circuit becomes more complicated.
【０００５】[0005]
【課題を解決するための手段】本発明は、第１のゲイン
を有する第１差動増幅回路と、前記第１のゲインより大
きい第２のゲインを有する第２差動増幅回路と、前記第
２のゲインより大きい第３のゲインを有する第３差動増
幅回路と、外部選択信号に応じて前記第１乃至第３差動
増幅回路のうち１つを動作させる動作制御回路と、前記
第１乃至第３差動増幅回路の出力信号が印加される共通
の出力回路とを備えることを特徴とする。The present invention provides a first differential amplifier having a first gain, a second differential amplifier having a second gain larger than the first gain, and A third differential amplifier circuit having a third gain greater than a gain of 2, an operation control circuit for operating one of the first to third differential amplifier circuits in response to an external selection signal; And a common output circuit to which an output signal of the third differential amplifier circuit is applied.
【０００６】また、第１入力信号が前記第１及び第３差
動増幅回路の共通の入力端子に印加され、第２入力信号
が前記第２差動増幅回路に印加されることを特徴とす
る。特に、前記切換回路は、ＡＭ及びＦＭバンドの受信
回路を備えるラジオ受信機において、共通のＩＦ信号ラ
インに導出される２以上のＩＦ信号を切り換えるために
用いられるものであり、前記第１入力信号をＡＭＩＦ信
号または第１ＦＭＩＦ信号とし、前記第２入力信号を第
２ＦＭＩＦ信号とすることを特徴とする。Also, a first input signal is applied to a common input terminal of the first and third differential amplifier circuits, and a second input signal is applied to the second differential amplifier circuit. . In particular, the switching circuit is used for switching between two or more IF signals led out to a common IF signal line in a radio receiver including an AM and FM band receiving circuit, and the first input signal Is an AMIF signal or a first FMIF signal, and the second input signal is a second FMIF signal.
【０００７】さらに、前記外部選択信号に応じて、ＡＭ
ＩＦ信号の場合前記第１差動増幅回路が選択され、第１
ＦＭ信号の場合前記第２差動増幅回路が選択され、さら
に第２ＦＭ信号の場合前記第３差動増幅回路が選択され
ることを特徴とする。また、前記第１差動増幅回路は、
エミッタ抵抗を介して差動接続されたトランジスタと、
前記トランジスタに接続された負荷とから成り、前記負
荷及びエミッタ抵抗の値によってゲインが決まり、前記
第２及び第３差動増幅回路は、差動接続されたトランジ
スタと、前記トランジスタに接続された負荷とから成
り、前記負荷の値によってゲインが決まることを特徴と
する。Further, according to the external selection signal, the AM
In the case of an IF signal, the first differential amplifier circuit is selected,
In the case of an FM signal, the second differential amplifier circuit is selected, and in the case of a second FM signal, the third differential amplifier circuit is selected. Further, the first differential amplifier circuit includes:
A transistor differentially connected via an emitter resistor;
A load connected to the transistor, wherein the gain is determined by the values of the load and the emitter resistance. The second and third differential amplifier circuits include a differentially connected transistor and a load connected to the transistor. Wherein the gain is determined by the value of the load.
【０００８】本発明によれば、第１乃至第３差動増幅回
路の動作を切り換えることにより、入力信号を切り換え
るとともに、入力に対するゲインが切り換わる。According to the present invention, by switching the operation of the first to third differential amplifier circuits, the input signal is switched and the gain for the input is switched.
【０００９】[0009]
【発明の実施の形態】図１は本発明の実施の形態を示す
図であり、１４は混合回路２からのＦＭまたは第1ＡＭ
ＩＦ信号が導出される１次コイル、１５及び１６は１次
コイル１４に対応する第１及び第２−２次コイル、１７
は第１−２次コイル１５に導出されるＩＦ信号が印加さ
れ、例えば中心周波数が１０．７ＭHzである広帯域フィ
ルタ、１８は第２−２次コイルに導出されるＩＦ信号が
印加され、例えば中心周波数が１０．７ＭHzで帯域幅が
広帯域フィルタ１７より狭い狭帯域フィルタ、１９は広
帯域フィルタ１７または狭帯域フィルタ１８の出力信号
を選択する選択回路、２０は受信回路の全体のゲインを
調整するためゲインが可変されるアンプ、２１は広帯域
及び狭帯域フィルタ１７及び１８とＩＦフィルタを成
し、アンプ２０の出力信号が印加されるフィルタ、２２
はＦＭ−ＩＦ信号の振幅レベルをリミットされるリミッ
タアンプ、２３は隣接妨害を検出する妨害検出回路、２
４は妨害の検出結果及び受信バンドの切り換えに応じて
ＩＦ信号の選択及びゲイン制御の命令を出力するマイコ
ン等の制御回路、２５は前記命令をデコードし、選択信
号ＳＬ及びゲイン制御信号ＧＡを発生する。尚、図１に
おいて、図２と同一の回路については、図１と同一の符
号を付す。FIG. 1 is a diagram showing an embodiment of the present invention. In FIG. 1, reference numeral 14 denotes an FM or first AM signal from a mixing circuit 2.
The primary coils from which the IF signal is derived, 15 and 16 are the first and second secondary coils corresponding to the primary coil 14, 17
Is a broadband filter having a center frequency of 10.7 MHz, for example, to which an IF signal derived to the secondary coil 15 is applied, and 18 is a broadband filter to which an IF signal derived to the secondary coil is applied. A narrow-band filter having a frequency of 10.7 MHz and a narrower bandwidth than the wide-band filter 17, a selection circuit 19 for selecting an output signal of the wide-band filter 17 or the narrow-band filter 18, and a gain 20 for adjusting the overall gain of the reception circuit Is an IF filter with the wide band and narrow band filters 17 and 18, and a filter to which the output signal of the amplifier 20 is applied,
Is a limiter amplifier that limits the amplitude level of the FM-IF signal, 23 is a disturbance detection circuit that detects adjacent disturbance,
Reference numeral 4 denotes a control circuit such as a microcomputer which outputs an IF signal selection and gain control instruction in accordance with the detection result of interference and switching of the reception band. 25 decodes the instruction and generates a selection signal SL and a gain control signal GA. I do. In FIG. 1, the same circuits as those in FIG. 2 are denoted by the same reference numerals as those in FIG.
【００１０】一般に、ＡＭ及びＦＭ受信回路の両方を有
するラジオ受信機は、ＡＭ受信時ＡＭ受信回路がオンし
ＦＭ受信回路がオフし、ＦＭ受信時ＦＭ受信回路がオン
しＡＭ受信回路がオフする。その為、ＡＭ受信時ＡＭの
ＲＦ及びＩＦ信号がＦＭ受信ラインに印加されることは
なく、ＦＭ受信時ＦＭのＲＦ及びＩＦ信号がＡＭ受信ラ
インに印加されることはない。Generally, in a radio receiver having both an AM and an FM receiving circuit, the AM receiving circuit is turned on and the FM receiving circuit is turned off at the time of AM reception, and the FM receiving circuit is turned on and the AM receiving circuit is turned off at the time of FM receiving. . Therefore, the AM RF and IF signals are not applied to the FM reception line during AM reception, and the FM RF and IF signals are not applied to the AM reception line during FM reception.
【００１１】制御回路２４に対してＡＭ受信に切り換え
る切換信号が印加されると、これに応じて命令１が出力
される。デコーダ２５で命令１がデコードされると、選
択信号ＳＬ及びゲイン制御信号ＧＡが発生する。選択信
号ＳＬに応じて選択回路１９は図示と逆の状態になり、
狭帯域フィルタ１８の出力信号が選択される。ここで、
混合回路２内のＦＭ及びＡＭ混合部３及び１０からのＩ
Ｆ信号は共通の出力回路となる１次コイル１４に導出さ
れる。さらに、２次コイル１５及び１６にはそれぞれ同
一なＩＦ信号が導出され、広帯域及び狭帯域フィルタ１
７及び１８で帯域制限される。広帯域及び狭帯域フィル
タ１７及び１８はそれぞれ図２アのようなフィルタ特性
を有している。第1ＡＭＩＦ信号の周波数は単一の１
０．７１ＭHzであるので第1ＡＭＩＦ信号の周波数帯域
を狭く制限しても良く、また、他の周波数信号により第
1ＡＭＩＦ信号の振幅に悪影響を与えないようにするた
め、第1ＡＭＩＦ信号の周波数帯域は狭く制限されるこ
とが望ましい。そこで、ＡＭ受信時、第1ＡＭＩＦ信号
として狭帯域フィルタ１８を通過したものが選択され
る。When a switching signal for switching to AM reception is applied to the control circuit 24, a command 1 is output in response thereto. When the instruction 1 is decoded by the decoder 25, a selection signal SL and a gain control signal GA are generated. In response to the selection signal SL, the selection circuit 19 is in a state opposite to that shown in the figure,
The output signal of the narrow band filter 18 is selected. here,
I from the FM and AM mixing units 3 and 10 in the mixing circuit 2
The F signal is led out to a primary coil 14 serving as a common output circuit. Further, the same IF signal is derived to the secondary coils 15 and 16, respectively, and the broadband and narrowband filters 1
Bands are limited at 7 and 18. The wideband and narrowband filters 17 and 18 each have filter characteristics as shown in FIG. The frequency of the first AMIF signal is a single 1
Since the frequency is 0.71 MHz, the frequency band of the first AMIF signal may be limited narrowly.
It is desirable that the frequency band of the first AMIF signal is narrowly limited so as not to adversely affect the amplitude of the first AMIF signal. Therefore, at the time of AM reception, a signal that has passed through the narrow-band filter 18 is selected as the first AMIF signal.
【００１２】また、ゲイン制御信号ＧＡに応じて増幅回
路２０のゲインは第１ゲインＧ１に設定される。増幅回
路２０は、第１ゲインＧ１と、第１ゲインより大きい第
２ゲインＧ２と、第２ゲインより大きい第３ゲインＧ３
とを有し、ゲイン制御信号ＧＡによりそのうちの１つの
ゲインに設定される。ＡＭ変調は一般に良く知られてい
るように単一周波数の搬送波信号を振幅変調されたもの
なので、ＡＭＩＦ信号のレベルがリミットされるとＡＭ
復調できない。そこで、第1ＡＭＩＦ信号がリミットさ
れないように最小の第１ゲインＧ１が選択される。狭帯
域フィルタ１８の出力信号は増幅回路２０で第１ゲイン
Ｇ１により増幅される。その後、増幅回路２０からの第
1ＡＭＩＦ信号は帯域制限された後、ＡＭ第２混合回路
１２で第２ＡＭＩＦ信号に周波数変換される。The gain of the amplifier circuit 20 is set to a first gain G1 according to the gain control signal GA. The amplifier circuit 20 includes a first gain G1, a second gain G2 larger than the first gain, and a third gain G3 larger than the second gain.
And the gain is set to one of the gains by the gain control signal GA. As is well known, AM modulation is obtained by amplitude-modulating a single-frequency carrier signal.
Cannot demodulate. Therefore, the minimum first gain G1 is selected so that the first AMIF signal is not limited. The output signal of the narrow band filter 18 is amplified by the amplifier circuit 20 with the first gain G1. After that, the second
After the band of the 1 AMIF signal is limited, the AM second mixer 12 frequency-converts the signal into a second AMIF signal.
【００１３】一方、制御回路２４に対してＦＭ受信に切
り換える切換信号が印加されると、これに応じて命令２
が出力される。デコーダ２５で命令２がデコードされる
と、他の選択信号ＳＬ及びゲイン制御信号ＧＡが発生す
る。選択信号ＳＬに応じて選択回路１９が図示の状態に
なり広帯域フィルタ１７の出力信号が選択される。ＦＭ
変調信号は一般に知られるように搬送波信号を周波数偏
移したものであるので、その周波数偏移範囲と略同一な
広帯域フィルタ１７を用いて、必要な信号だけを通過さ
せている。広帯域フィルタ１７からのＦＭＩＦ信号は、
増幅回路２０でゲイン制御信号ＧＡに応じて設定された
第２ゲインＧ２により増幅される。増幅されたＦＭＩＦ
信号はフィルタ２１で帯域制限され、その後リミッタア
ンプでそのレベルがリミットされる。On the other hand, when a switching signal for switching to FM reception is applied to the control circuit 24, a command 2
Is output. When the instruction 2 is decoded by the decoder 25, another selection signal SL and a gain control signal GA are generated. In response to the selection signal SL, the selection circuit 19 enters the state shown in the figure, and the output signal of the broadband filter 17 is selected. FM
Since the modulated signal is obtained by shifting the frequency of a carrier signal as is generally known, only a necessary signal is passed through the wideband filter 17 having substantially the same frequency shift range. The FMIF signal from the broadband filter 17 is
The signal is amplified by the amplifier circuit 20 with the second gain G2 set according to the gain control signal GA. Amplified FMIF
The signal is band-limited by the filter 21 and then its level is limited by a limiter amplifier.
【００１４】ＦＭ受信時、希望局Ｆｄに隣接して妨害局
Ｆｕｄが発生したとする。この妨害局Ｆｕｄは図２イの
ように広帯域フィルタ１７の通過帯域内で、かつ、狭帯
域フィルタ１８の通過帯域外にある。妨害検出回路２３
において、例えば選択回路１９以降のＦＭＩＦ信号のレ
ベルや、広帯域及び狭帯域フィルタ１７及び１８の出力
レベルの関係を見ることにより、隣接妨害が検出される
と、検出信号DETが発生し、これに基づいて制御回路２
４が命令３を出力する。命令３がデコードされて得られ
た選択信号ＳＬに応じて、選択回路１９は狭帯域フィル
タ１８の出力信号を選択する。狭帯域フィルタ１８では
妨害局Ｆｕｄはその通過帯域外になるので、妨害局Ｆｕ
ｄは狭帯域フィルタ１８で除去される。その結果、選択
されたＦＭＩＦ信号は妨害局が除去された状態の信号と
なる。また、ゲイン制御信号ＧＡにより増幅回路２０の
ゲインは第３ゲインＧ３に設定される。ＦＭＩＦ信号は
増幅回路２０の第３ゲインＧ３により増幅された後、フ
ィルタ２１で帯域制限され、リミッタアンプ２０でリミ
ットされる。よって、狭帯域フィルタ１８の出力信号を
選択するとＦＭＩＦ信号の一部が失われ、ＦＭ検波信号
に悪影響を与えるが、それよりも隣接妨害信号の除去に
よる効果の方が大きい。It is assumed that an interference station Fud is generated adjacent to the desired station Fd during FM reception. This interfering station Fud is within the pass band of the wide band filter 17 and outside the pass band of the narrow band filter 18 as shown in FIG. Interference detection circuit 23
In the above, for example, by detecting the level of the FMIF signal after the selection circuit 19 and the output level of the wideband and narrowband filters 17 and 18, if adjacent interference is detected, a detection signal DET is generated. Control circuit 2
4 outputs instruction 3. The selection circuit 19 selects the output signal of the narrow band filter 18 according to the selection signal SL obtained by decoding the instruction 3. In the narrow-band filter 18, the jamming station Fud is out of the pass band, so
d is removed by the narrow band filter 18. As a result, the selected FMIF signal is a signal from which the interfering station has been removed. The gain of the amplifier circuit 20 is set to the third gain G3 by the gain control signal GA. After the FMIF signal is amplified by the third gain G3 of the amplifier circuit 20, the band is limited by the filter 21 and is limited by the limiter amplifier 20. Therefore, when the output signal of the narrow band filter 18 is selected, a part of the FMIF signal is lost, which adversely affects the FM detection signal. However, the effect of removing the adjacent interference signal is greater than that.
【００１５】ここで、図２アに示されるように狭帯域フ
ィルタ１８の通過帯域の減衰量は広帯域フィルタより大
きいので、隣接妨害発生時のＦＭＩＦ信号のレベルは通
常受信時より低くなる。そこで、狭帯域フィルタ１８の
出力信号が選択された場合に、増幅回路２０のゲインを
第２ゲインＧ２より大きい第３ゲインＧ３に設定するこ
とにより、減衰量の増加が補正され、ＦＭＩＦ信号がよ
り大きいレベルに増幅される。その結果、通常受信時で
も隣接妨害発生時でも、増幅回路２０の出力レベルは変
わらず、ＦＭ受信系統のトータルゲインは変わらないよ
うにすることができる。但し、第２及び第３ゲインＧ２
及びＧ３の差は広帯域及び狭帯域フィルタ１７及び１８
の通過帯域における減衰量の差に略等しくなるように設
定される。Here, as shown in FIG. 2A, since the attenuation of the pass band of the narrow band filter 18 is larger than that of the wide band filter, the level of the FMIF signal when adjacent interference occurs is lower than that during normal reception. Therefore, when the output signal of the narrow band filter 18 is selected, the gain of the amplifier circuit 20 is set to the third gain G3, which is larger than the second gain G2, so that the increase in the attenuation is corrected, and the FMIF signal is further reduced. Amplified to a large level. As a result, the output level of the amplifier circuit 20 does not change and the total gain of the FM receiving system does not change during normal reception or when adjacent interference occurs. However, the second and third gains G2
And G3 is the difference between the wideband and narrowband filters 17 and 18
Are set so as to be substantially equal to the difference between the attenuation amounts in the passbands.
【００１６】図３は図１の選択回路１９及び増幅回路２
０の兼用となる具体回路を示す図であり、２６はトラン
ジスタＱ１及びＱ２が差動接続され、負荷として直列接
続された抵抗Ｒ１及びＲ２が接続されるとともに、第３
ゲインＧ３を有する差動増幅回路、２７はトランジスタ
Ｑ３及びＱ４が抵抗Ｒ３を介して差動接続され、負荷と
して抵抗Ｒ１が接続されるとともに、第１ゲインＧ１を
有する差動増幅回路、２８はトランジスタＱ５及びＱ６
が差動接続され、負荷として抵抗Ｒ１が接続されるとと
もに、第２ゲインＧ２を有する差動増幅回路、２９はエ
ミッタフォロワ型のトランジスタＱ７で構成され、差動
増幅回路２６乃至２８の出力信号を後段の回路に出力す
るための共通の出力段回路、３０乃至３２は差動増幅回
路２６乃至２８に対して同一の動作電流を発生する電流
源、３３はデコーダ２５から出力される２ビットの切換
信号に応じて電流源３０乃至３２を切り換える切換回路
である。また、狭帯域フィルタ１７の出力信号は差動増
幅回路２６及び２７に印加され、広帯域フィルタ１８の
出力信号は差動増幅回路２８に印加されている。FIG. 3 shows the selection circuit 19 and the amplification circuit 2 of FIG.
FIG. 26 is a diagram showing a specific circuit shared with 0, in which a transistor Q1 and a transistor Q2 are differentially connected, and resistors R1 and R2 connected in series as a load are connected;
A differential amplifier circuit having a gain G3, 27 is a differential amplifier circuit having transistors Q3 and Q4 differentially connected via a resistor R3, a resistor R1 connected as a load, and having a first gain G1, and 28 is a transistor. Q5 and Q6
Are differentially connected, a resistor R1 is connected as a load, and a differential amplifier circuit having a second gain G2. An emitter-follower transistor Q7 29 is used to output signals from the differential amplifier circuits 26 to 28. A common output stage circuit for outputting to the subsequent circuit, 30 to 32 are current sources for generating the same operating current for the differential amplifier circuits 26 to 28, and 33 is a 2-bit switch output from the decoder 25. This is a switching circuit that switches the current sources 30 to 32 according to a signal. The output signal of the narrow band filter 17 is applied to differential amplifier circuits 26 and 27, and the output signal of the wide band filter 18 is applied to a differential amplifier circuit 28.
【００１７】まず、ＡＭ受信時、切換信号が（０、０）
となると、切換回路３３の可動端子は電流源３１側に接
続されるので差動増幅回路２７が動作する。よって、狭
帯域フィルタ１８からのＡＭＩＦ信号が抵抗Ｒ１及びＲ
３で定まる第１ゲインＧ１で増幅され、出力段回路２９
に印加される。また、ＦＭ通常受信時、切換信号が
（１、０）となると、切換回路３３は電流源３２側に切
り換わり、差動増幅回路２８が動作する。よって、広帯
域フィルタ１７からのＦＭＩＦ信号が抵抗Ｒ１で定まる
第２ゲインで増幅される。さらに、ＦＭ受信時隣接妨害
が発生すると、切換信号が（１、１）になり、切換回路
３３が電流源３０に切り換わるので、差動増幅回路２６
が動作する。その結果、狭帯域フィルタ１８のＦＭＩＦ
信号が抵抗Ｒ１及びＲ２で定まる第３ゲインによって増
幅される。First, at the time of AM reception, the switching signal is (0, 0).
Then, the movable terminal of the switching circuit 33 is connected to the current source 31 side, so that the differential amplifier circuit 27 operates. Therefore, the AMIF signal from the narrow band filter 18 is connected to the resistors R1 and R1.
3 is amplified by the first gain G1 determined by
Is applied to When the switching signal becomes (1, 0) during FM normal reception, the switching circuit 33 switches to the current source 32 side, and the differential amplifier circuit 28 operates. Therefore, the FMIF signal from the broadband filter 17 is amplified with the second gain determined by the resistor R1. Further, when adjacent interference occurs during FM reception, the switching signal becomes (1, 1), and the switching circuit 33 switches to the current source 30.
Works. As a result, the FMIF of the narrow band filter 18
The signal is amplified by a third gain determined by the resistors R1 and R2.
【００１８】ところで、図３の差動増幅回路のゲインは
主に負荷によって決まる。差動増幅回路２６及び２８に
おいて、例えば、トランジスタＱ１及びＱ５のコレクタ
電流をそれぞれＩｃとすると、差動増幅回路２６の出力
電圧はＩｃ−（Ｒ１＋Ｒ２）×Ｉ０となり、差動増幅回
路２８の出力電圧はＩｃ−Ｒ１×Ｉ０となる。（Ｒ１＋
Ｒ２）＞Ｒ１より、同一レベルの入力信号に対して、差
動増幅回路２６の出力レベルは差動増幅回路２８より高
くなる。また、差動増幅回路２７及び２８の負荷はとも
に抵抗Ｒ１である。しかし、差動増幅回路２７にはエミ
ッタ抵抗Ｒ３が接続されるので、トランジスタＱ３及び
Ｑ４のエミッタ間の電圧差をΔＶとすると、トランジス
タＱ３及びＱ４のエミッタ電流はＩ＝ΔＶ／Ｒ３とな
り、抵抗Ｒ３によって制限される。よって、同一の入力
信号に対して、トランジスタＱ３のコレクタ電流はトラ
ンジスタＱ５よりも小さく、差動増幅回路２８の出力レ
ベルは差動増幅回路２７より高い。上記より、差動増幅
回路２６乃至２８のゲインは、第１ゲインＧ１＜第２ゲ
インＧ２＜第３ゲインＧ３となる。Incidentally, the gain of the differential amplifier circuit shown in FIG. 3 is mainly determined by the load. In the differential amplifier circuits 26 and 28, for example, assuming that the collector currents of the transistors Q1 and Q5 are respectively Ic, the output voltage of the differential amplifier circuit 26 is Ic− (R1 + R2) × I0, and the output voltage of the differential amplifier circuit 28 is Is Ic−R1 × I0. (R1 +
R2)> R1, the output level of the differential amplifier circuit 26 is higher than that of the differential amplifier circuit 28 for input signals of the same level. The loads on the differential amplifier circuits 27 and 28 are both resistors R1. However, since the emitter resistor R3 is connected to the differential amplifier circuit 27, if the voltage difference between the emitters of the transistors Q3 and Q4 is ΔV, the emitter currents of the transistors Q3 and Q4 are I = ΔV / R3, and the resistor R3 Limited by Therefore, for the same input signal, the collector current of transistor Q3 is smaller than that of transistor Q5, and the output level of differential amplifier circuit 28 is higher than that of differential amplifier circuit 27. From the above, the gains of the differential amplifier circuits 26 to 28 satisfy the first gain G1 <the second gain G2 <the third gain G3.
【００１９】従って、図３の回路では差動増幅回路を切
り換えると、入力信号を切り換えることができるととも
に、入力信号に対応したゲインも切り換えることができ
る。尚、切換信号は２ビットで構成されており、切り換
え信号を図１の選択信号ＳＬ及びゲイン制御信号ＧＡを
１つとしてまとめた信号としても可能である。Therefore, in the circuit of FIG. 3, when the differential amplifier circuit is switched, the input signal can be switched, and the gain corresponding to the input signal can also be switched. The switching signal is composed of two bits, and the switching signal can be a signal obtained by combining the selection signal SL and the gain control signal GA of FIG.
【００２０】[0020]
【発明の効果】本発明によれば、簡単な構成で、受信バ
ンドの切り換え及び隣接妨害対策の両方を施すことがで
きる。特に、ＦＭ及びＡＭ受信回路において、図３の切
換回路では、簡単な構成で、ＡＭＩＦ信号とＦＭＩＦ信
号とを確実に切り換えることができるとともに、ゲイン
も切り換わり、ラジオ受信機のトータルゲインをＡＭ及
びＦＭ受信における所望のゲインに設定することができ
る。According to the present invention, both the switching of the reception band and the countermeasure against adjacent interference can be performed with a simple configuration. In particular, in the FM and AM receiving circuits, the switching circuit of FIG. 3 can reliably switch between the AMIF signal and the FMIF signal with a simple configuration, and the gain is also switched, so that the total gain of the radio receiver is reduced to AM and AM. A desired gain in FM reception can be set.
【図１】本発明の実施の形態を示すブロック図である。FIG. 1 is a block diagram showing an embodiment of the present invention.
【図２】図１の動作を説明するための特性図である。FIG. 2 is a characteristic diagram for explaining the operation of FIG.
【図３】図１の選択回路１９及び増幅回路２０の具体回
路を示す回路図である。FIG. 3 is a circuit diagram showing specific circuits of a selection circuit 19 and an amplification circuit 20 of FIG.
【図４】従来例を示すブロック図である。FIG. 4 is a block diagram showing a conventional example.
【符号の説明】 １７ 広帯域フィルタ １８ 狭帯域フィルタ １９ 選択回路 ２０ 増幅回路 ２１ フィルタ ２２ リミッタアンプ ２３ 妨害検出回路 ２４ 制御回路 ２５ デコーダ[Description of Signs] 17 Wideband filter 18 Narrowband filter 19 Selection circuit 20 Amplification circuit 21 Filter 22 Limiter amplifier 23 Interference detection circuit 24 Control circuit 25 Decoder
Claims (5)
と、 前記第１のゲインより大きい第２のゲインを有する第２
差動増幅回路と、 前記第２のゲインより大きい第３のゲインを有する第３
差動増幅回路と、 外部選択信号に応じて前記第１乃至第３差動増幅回路の
うち１つを動作させる動作制御回路と、 前記第１乃至第３差動増幅回路の出力信号が印加される
共通の出力回路とを備えることを特徴とする切換回路。A first differential amplifier circuit having a first gain; and a second differential amplifier circuit having a second gain larger than the first gain.
A third amplifier having a third gain larger than the second gain;
A differential amplifier circuit, an operation control circuit that operates one of the first to third differential amplifier circuits according to an external selection signal, and an output signal of the first to third differential amplifier circuits is applied. And a common output circuit.
幅回路の共通の入力端子に印加され、第２入力信号が前
記第２差動増幅回路に印加されることを特徴とする請求
項１記載の切換回路。2. A method according to claim 1, wherein a first input signal is applied to a common input terminal of said first and third differential amplifier circuits, and a second input signal is applied to said second differential amplifier circuit. The switching circuit according to claim 1.
受信回路を備えるラジオ受信機において、共通のＩＦ信
号ラインに導出される２以上のＩＦ信号を切り換えるた
めに用いられるものであり、 前記第１入力信号をＡＭＩＦ信号または第１ＦＭＩＦ信
号とし、前記第２入力信号を第２ＦＭＩＦ信号とするこ
とを特徴とする請求項２記載の切換回路。3. The switching circuit according to claim 1, wherein the switching circuit is used to switch two or more IF signals derived to a common IF signal line in a radio receiver including an AM and FM band receiving circuit. 3. The switching circuit according to claim 2, wherein one input signal is an AMIF signal or a first FMIF signal, and the second input signal is a second FMIF signal.
号の場合前記第１差動増幅回路が選択され、第１ＦＭ信
号の場合前記第２差動増幅回路が選択され、さらに第２
ＦＭ信号の場合前記第３差動増幅回路が選択されること
を特徴とする請求項３記載の切換回路。4. In response to the external selection signal, the first differential amplifier circuit is selected for an AMIF signal, the second differential amplifier circuit is selected for a first FM signal, and a second
4. The switching circuit according to claim 3, wherein said third differential amplifier circuit is selected for an FM signal.
を介して差動接続されたトランジスタと、前記トランジ
スタに接続された負荷とから成り、前記負荷及びエミッ
タ抵抗の値によってゲインが決まり、 前記第２及び第３差動増幅回路は、差動接続されたトラ
ンジスタと、前記トランジスタに接続された負荷とから
成り、前記負荷の値によってゲインが決まることを特徴
とする請求項１記載の切換回路。5. The first differential amplifier circuit includes a transistor differentially connected via an emitter resistor, and a load connected to the transistor, and a gain is determined by a value of the load and the emitter resistance. 2. The switching device according to claim 1, wherein each of the second and third differential amplifier circuits includes a differentially connected transistor and a load connected to the transistor, and a gain is determined by a value of the load. circuit.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP3614398A JPH11234161A (en) | 1998-02-18 | 1998-02-18 | Switching circuit |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP3614398A JPH11234161A (en) | 1998-02-18 | 1998-02-18 | Switching circuit |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH11234161A true JPH11234161A (en) | 1999-08-27 |
Family
ID=12461580
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP3614398A Pending JPH11234161A (en) | 1998-02-18 | 1998-02-18 | Switching circuit |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH11234161A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2009004933A1 (en) * | 2007-07-05 | 2009-01-08 | Nsc Co., Ltd. | Am/fm radio receiver and receiving semiconductor integrated circuit used for same |
-
1998
- 1998-02-18 JP JP3614398A patent/JPH11234161A/en active Pending
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2009004933A1 (en) * | 2007-07-05 | 2009-01-08 | Nsc Co., Ltd. | Am/fm radio receiver and receiving semiconductor integrated circuit used for same |
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