!twf.doc/c 九、發明說明： 【發明所屬之技術領域】 本發明是有關於-種可控制之增益電路，且特別是有 關於-種自動增益㈣電路及其自練減電路與可變衰減 器。 【先前技術】 自動增益控制電路常常被應用在傳輸系統中。在不同 =環境、狀況下，傳輸系統所獲得之輸入訊號往往是不穩 疋的，因此需要自動增益控制電路自動改變不同的系統增 益以完成穩定的傳輸工作。傳統的自動增益控制電路是在 放大态之輸出端加上自動衰減電路，如圖1A所示。 圖1A疋傳統自動增益控制電路方塊圖。請參照圖 1A，不穩定的輸入訊號Vin先經由放大器11()將訊號放 大後，再由可變衰減器120與訊號偵測器13〇所組成的自 動衰減電路依照輸入訊號Vin之大小適度地衰減被放大的 輸入§fL號111 ’因此得到不同的增益量而可以輸出穩定之 輸出訊號Vout。 傳統的自動衰減電路由可變衰減器120與訊號偵測器 130所組成。其中，可變衰減器12〇可視為一種變形之万 型衰減器，係隨著控制訊號Vcon升高而減少其衰減量， 其衰減量與控制訊號之關係如圖1B所示。另外，傳統訊 號偵測器130在偵測訊號時，若輸入訊號Vin越大，則訊 號偵測器130所輸出之控制訊號Vcon越小。如圖所示， 傳統訊號债測器130經由微帶線(microstrip line) 131之一 1281314 14572twf.doc/c 端接收輸出訊號V〇Ut，而微帶線131之另一端則與二極 體132之陰極相耦接。電容133之一端耦接至二極體132 之陽極，而另一端則接地。其中，二極體132陽極之訊號 即為控制訊號Vcon。 口此’ ^輸入式號Vin越大，則控制訊號vc〇n越小， 進而控制可變衰減器120使其訊號衰減量增加，故使得傳 統自動增益控制電路100之整體增益降低。反之，當輸入 Λ號Vin變小，則控制訊號vcon升高，進而控制可變衰 減為120使其訊號衰減量減少，故使得自動增益控制電路 100之整體增益增加。 然而，在某些設計需求下，若訊號偵測器所輸出之控 制訊號是隨著輸人訊賴大㈣高，麟統的 路將無法適用。 風 【發明内容】 本發明的目的就是在提供一種自動衰減電路，以適用 於使控制λ號與輸入说號成正比之訊號彳貞測器。 本發明的再-目的是提供一種自動衰減電路 中諸目的外’以更簡單之電路架構自動進行訊號衰減。 本發明的又-目的是提供一種可變衰 減量與控制訊號電位成正比。 Λ使其哀 本發明的另-目的是提供一種自動增益控制以 在不大幅改變自動增益㈣㈣構下亦可 號成正比之訊號偵測器。 。用，、輸入七!twf.doc/c IX. Description of the Invention: [Technical Field of the Invention] The present invention relates to a controllable gain circuit, and more particularly to an automatic gain (four) circuit and its self-reduction circuit and Variable attenuator. [Prior Art] Automatic gain control circuits are often used in transmission systems. In different environments and conditions, the input signals obtained by the transmission system are often unstable. Therefore, automatic gain control circuits are required to automatically change different system gains to achieve stable transmission. A conventional automatic gain control circuit is provided with an automatic attenuation circuit at the output of the amplified state, as shown in Fig. 1A. Figure 1A is a block diagram of a conventional automatic gain control circuit. Referring to FIG. 1A, the unstable input signal Vin first amplifies the signal through the amplifier 11 (), and then the automatic attenuating circuit composed of the variable attenuator 120 and the signal detector 13 适 is appropriately according to the magnitude of the input signal Vin. Attenuation of the amplified input §fL number 111 ' thus gives a different amount of gain and can output a stable output signal Vout. The conventional automatic attenuation circuit is composed of a variable attenuator 120 and a signal detector 130. The variable attenuator 12 can be regarded as a deformed type of attenuator, which reduces the attenuation amount as the control signal Vcon rises, and the relationship between the attenuation amount and the control signal is as shown in FIG. 1B. In addition, when the conventional signal detector 130 detects the signal, if the input signal Vin is larger, the control signal Vcon outputted by the signal detector 130 is smaller. As shown, the conventional signal detector 130 receives the output signal V〇Ut via one of the 1281314 14572twf.doc/c terminals of the microstrip line 131, and the other end of the microstrip line 131 is connected to the diode 132. The cathode is coupled. One end of the capacitor 133 is coupled to the anode of the diode 132, and the other end is grounded. The signal of the anode of the diode 132 is the control signal Vcon. The larger the input type Vin, the smaller the control signal vc〇n, and thus the variable attenuator 120 is controlled to increase the signal attenuation amount, so that the overall gain of the conventional automatic gain control circuit 100 is lowered. On the other hand, when the input apostrophe Vin becomes smaller, the control signal vcon rises, and the variable attenuation is controlled to 120 to reduce the signal attenuation amount, so that the overall gain of the automatic gain control circuit 100 is increased. However, under certain design requirements, if the control signal output by the signal detector is higher than the input (4), the system will not be applicable. Wind [Disclosure] It is an object of the present invention to provide an automatic attenuation circuit for use in a signal detector that controls the lambda number to be proportional to the input number. It is a further object of the present invention to provide an automatic attenuation circuit that automatically performs signal attenuation with a simpler circuit architecture. It is yet another object of the present invention to provide a variable attenuation that is proportional to the control signal potential. Another object of the present invention is to provide an automatic gain control to be proportional to the signal detector without significantly changing the automatic gain (4) (4). . Use, enter seven
I2813H/C 、本f明的另一目的是提供一種自動增益控制電路，除 亡述中諸目的外，以更簡單之電路架構自動調整訊號增 本發明提出一種自動衰減電路，包括可變衰減器、訊 號偵測，及反相緩娜。可魏減it衰減輸人訊號。訊 號偵測益耦接至可變衰減器，用以偵測可變衰減器之輸出 並且輸出第一控制訊號。反相缓衝器耦接至可變衰減器以 及訊號偵測器，用以將第一控制訊號反相以輸出第二二制 訊號。其中，可變衰減器係依照第二控制訊號決定其^減 輸入訊號之衰減量。 入訊號，以產生輸出訊號。訊號偵測器耦接至可變衰減器， 用以偵測可變衰減器之輸出訊號並且輸出控制訊號。其 中，當輸入訊號越大，則控制訊號隨之越大，而可變衰減 器依照控制訊號決定其衰減輸入訊號之衰減量。 本發明提出另一種自動衰減電路，應用於自動增益控 制，包括可變衰減器以及訊號偵測器。可變衰減器^減^ 本發明另提出^一種可、交哀減裔’用以依據控制訊號衰 減輸入訊號，以產生輸出訊號。可變衰減器包括第一〜第 三射頻阻流器(RF choke)、第 第四二極體、第一及第 二電阻以及第一〜第四電容。第一射頻阻流器之第一端接 收控制訊號。第二射頻阻流器之第一端耦接至第一射頻阻 流器之第二端。第三射頻阻流器之第一端輕接至第一電壓 線。第一二極體之陰極輛接至弟一射頻阻流器之第二端， 以及第一二極體之陽極耦接至第三射頻阻流器之第一端。 7 1281314 14572twf.doc/c 第二二極體之陰極耦接至第二射 第二二極體之陽_接至第：射之弟二端，以及 二極體之陽極耦接至第一二極體之险，弟二 極耦接至第二二極體之陰極。第:極體之陽 二-，體之陰極H阻之第二端_至第二電 ^-電阻之第-端叙接至第四二極體之陰極，第二電阻之 第^祕至第二電壓線。第—電容之第— =之陰極’第—電容之第二端祕至第二電>1線; -電谷之第-翻接至第四二極體之陰極，第二電容之 二端祕至第二電壓線。第三電容之第—端輕接至第一二 極體之陰極’第三電容之第二端接收輸入訊號。第四電容 之第Μ麵接至第一二極體之陰極，第四電容之第-端 訊號為輸出訊號。 弟一^之 本發明另提出一種自動增益控制電路，包括放大器、 可變衰減器、訊號偵測器以及反相緩衝器。放大器增^輸 入訊號並輸出被增益輸入訊號。可變衰減器耦接至放^ ，，用以衰減被增益輸入訊號以產生輸出訊號。訊號偵測 器耦接至可變衰減器，用以偵測可變衰減器之輸出訊號並 且輸出第一控制訊號。反相緩衝器耦接至可變衰減器以及 訊號偵測器，用以將第一控制訊號反相以輸出第二控制訊 號。其中，可變衰減器係依照第二控制訊號決定衰減輸入 訊號之衰減量。 本發明提出另一種自動增益控制電路，包括放大器、 可變衰減器以及訊號偵測器。放大器增益輸入訊號並輸出 l28imtwf,〇c/c 被增益輸入訊號。可變衰減器耦接至放大器，用以衰減被 增益輸入訊號以產生輸出訊號。訊號價測器耗接至可變衰 減器，用以偵測可變衰減器之輸出訊號並且輸出控制訊 號。其中，當輸入訊號越大’則控制訊號隨之越大，而可 變衰減器依照控制訊號決定衰減輸入訊號之衰減量。 本發明因利用反相缓衝器將與輸入訊號成正比之第— 控制訊號轉換為與輸入訊號成反比之第二控制訊號，因此 在不大幅改變自動增益控制的架構下亦可以應用與輸入訊 號成正比之訊號偵測器。再者，衰減器所需的電流係由反 相緩衝器所提供，故足夠的電流可以讓衰減器達到更大衰 減範圍(dynamic range)。另外，本發明因使用其衰減量與 控制訊號成正比之可變衰減器，因此更可省去反相緩衝器 而直接接收與輸入訊號成正比之控制訊號，以節省成本。 為讓本發明之上述和其他目的、特徵和優點能更明顯 易懂，下文特舉較佳實施例，並配合所附圖式，作詳細說 明如下。 【實施方式】 圖2A疋依照本發明之一實施例所繪示之一種自動增 盃控制電路方塊圖。請參照圖2A，為方便說明本發明， 在本實施例中自動增益控制電路2〇〇例如被應用於無線傳 輸系統中。在不同的環境與狀況下，無線傳輸系統所獲得 之輪入訊號(Vin)往往是不穩定的，因此需要自動增益控 制電路200自動改變系統增益以產生穩定的訊號（即圖中 之輪出訊號Vout)。 1281314 14572twf.doc/c 自動增益控制電路200包括放大器210與自動衰減電 路220。由放大器210將不穩定的輸入訊號Vin放大(增 益）預定之固定倍率後輸出輸入訊號211，再由自動衰減 電路220視輸入訊號大小適當地衰減被增益的輸入訊號 211後產生穩定的輸出訊號Vout。其中，自動衰減電路220 包括可變衰減器230、訊號偵測器240以及反相緩衝器 250。 可變衰減器230將被增益之輸入訊號211加以衰減以 產生輸出訊號Vout。訊號偵測器240則偵測可變衰減器230 所產生之輸出訊號Vout以輸出第一控制訊號241，其中 第一控制訊號241例如是一種電壓訊號，並且第一控制訊 號241係與輸入訊號vin成正比。反相緩衝器250將第一 控制訊號241反相以輸出第二控制訊號251，在此第二控 制訊號251之電壓例如為X_nV，其中v表示第一控制訊 號241之電壓，n表示欲改變電壓v之控制倍率係數，X 則表示可變衰減器230可控制範圍之最高電壓。當輸入訊 唬最弱時，同時衰減器之衰減量也最少，可得到訊號偵測 裔240輸出為Vmin，令X=nVmin，便可求出n=x/vmin。 換句話說，第二控制訊號251與輸入訊號vin成反比， 因此可以應用其訊號衰減量與控制電壓成反比之可變衰減 器230而依照第二控制訊號251決定訊號衰減量。 圖2B是圖2A之自動增益控制電路2〇〇的範例電路 圖。其中可變衰減器230例如以圖1A中傳統可變衰減器 120實施之，故不在此贅述。訊號偵測器24〇例如以微帶 1281314 14572twf.doc/c 線(microstrip line) 242、二極體243以及電容244所組成。 吼號偵測為240經由微帶線242之一端接收輸出訊號 Vout，而微帶線242之另一端則與二極體243之陽極相耦 接。電容244之一端耦接至二極體243之陰極，而另一端 則接地。其中，二極體243陰極之訊號即為第一控制訊號 241。因此，第一控制訊號241電壓將隨著輸入訊號vin 增強而升尚，反之亦隨著輸入訊號Vin減弱而降低電壓。 反相緩衝器250例如以可變電阻252、電阻253與pNp 電晶體254所組成。可變電阻252具有第一終端&、第二 終端b以及滑動端c，用以依照滑動端c之位置決定其第 一終端a至滑動端c之間阻值R2以及滑動端c至第二終 端b之間阻值R3。可變電阻252之第一終端&接收第一 控制訊號241。電阻253之一端耦接至可變電阻252之第 二終端、b ’而電阻253之另一端則輕接至第一電壓線(在 此例如，電源電壓線）。電阻253在此作為限流電阻，其 J影響，減器的控制範圍。電阻253之阻值R1越大，所 付到的衰減動態範圍會越A，但相制平觸耗電流合 越大:因此必須選取-個平衡點。電晶體254之基極^ ，可、交私阻252之滑動端c，射極耦接至可變電阻之 第一終鈿b，集極輸出第二控制訊號251。 上述可交電阻252之兩端電阻R2與R3是影塑 倍率係數η及衰減值的偏移量。若可變電阻况之^值 ’則初始衰減量(衰減器之初始值)會提高， 控抓率係數η也會增加。S R2+R3選取較小的值，則 1281314 14572twf.doc/c 初始衰減里與控制倍率係數就較低。其次是以2與^^ =比例遥取’若R2增大而R3減小，則會增加初始衰減 虿並且減少控制倍率係數n。反之，若R2減小而R3增 大，則會減少初始衰減量並且增加控制倍率係數n。 …R2與R3之總值與個別值對初始衰減量以及控制倍 率係數η的變化比例不盡相同，因此必須依不同條件選取 適§值。若電路經常性需要調整，則反相緩衝器可依 照圖2Β所示以可變電阻252實施之。若為固定條件使用 下的電路，則阻值R2與R3可採用固定電阻實施之，以 降低電路成本。如圖2C所示，該圖是圖2Α自動增益控 制電路200中反相緩衝器250的另一範例電路圖。 上述實施例中係使用其衰減量與控制電壓成反比（如 圖1Β所示)之傳統可變衰減器，因此當訊號偵測器所輸出 之控制訊號係與輸入訊號成正比時，便需要反相緩衝哭調 整控制訊號。以下另一實施例將說明使用其衰減量與控制 電壓成正比之可變衰減器，因此可配合所輸出之控制^號 與輸入訊號成正比之訊號偵測器，以省去反相緩衝器以及 降低成本。 圖3Α是依照本發明之一實施例所繪示之另一種自動 增益控制電路方塊圖。請參照圖3Α，自動增益控制電路 300包括放大器310與自動衰減電路320。由放大器31〇 將不穩定的輸入訊號Vin放大(增益)預定之固定倍率後輸 出輸入訊號311，再由自動衰減電路320視輸入訊號大小 適當地衰減被增益的輸入訊號311後產生穩定的輸出訊號 12 i28imcAnother object of the I2813H/C and the present invention is to provide an automatic gain control circuit which automatically adjusts the signal by a simpler circuit structure in addition to the objects described in the description. The invention provides an automatic attenuation circuit, including a variable attenuator. , signal detection, and reverse phase. Wei can reduce it to attenuate the input signal. The signal detection is coupled to the variable attenuator for detecting the output of the variable attenuator and outputting the first control signal. The inverting buffer is coupled to the variable attenuator and the signal detector for inverting the first control signal to output the second binary signal. The variable attenuator determines the attenuation of the input signal according to the second control signal. Enter the signal to generate an output signal. The signal detector is coupled to the variable attenuator for detecting the output signal of the variable attenuator and outputting the control signal. Among them, when the input signal is larger, the control signal is larger, and the variable attenuator determines the attenuation of the attenuation input signal according to the control signal. The present invention proposes another automatic attenuation circuit for automatic gain control, including variable attenuators and signal detectors. The variable attenuator ^ reduction ^ The present invention further proposes a type of singularity for reducing the input signal according to the control signal to generate an output signal. The variable attenuator includes first to third RF chokes, a fourth diode, first and second resistors, and first to fourth capacitors. The first end of the first RF choke receives the control signal. The first end of the second RF choke is coupled to the second end of the first RF block. The first end of the third RF choke is lightly connected to the first voltage line. The cathode of the first diode is connected to the second end of the RF blocker, and the anode of the first diode is coupled to the first end of the third RF block. 7 1281314 14572twf.doc/c The cathode of the second diode is coupled to the anode of the second second diode. The second end of the second diode is connected to the second end of the second body, and the anode of the diode is coupled to the first two. In the case of the polar body, the second pole is coupled to the cathode of the second diode. No.: the second body of the polar body, the second end of the cathode H of the body _ to the second end of the second electric resistance is connected to the cathode of the fourth diode, and the second resistor is the second to the second Voltage line. The first - the first of the capacitor - = the cathode 'the second end of the capacitor to the second electric > 1 line; - the first of the electric valley - flipped to the cathode of the fourth diode, the second end of the second capacitor Secret to the second voltage line. The first end of the third capacitor is lightly connected to the cathode of the first diode. The second end of the third capacitor receives the input signal. The third surface of the fourth capacitor is connected to the cathode of the first diode, and the first end signal of the fourth capacitor is an output signal. The invention further provides an automatic gain control circuit comprising an amplifier, a variable attenuator, a signal detector and an inverting buffer. The amplifier adds an input signal and outputs a gain input signal. The variable attenuator is coupled to the amplifier to attenuate the gain input signal to generate an output signal. The signal detector is coupled to the variable attenuator for detecting the output signal of the variable attenuator and outputting the first control signal. The inverting buffer is coupled to the variable attenuator and the signal detector for inverting the first control signal to output the second control signal. The variable attenuator determines the attenuation of the attenuated input signal according to the second control signal. The present invention proposes another automatic gain control circuit including an amplifier, a variable attenuator, and a signal detector. The amplifier gains the input signal and outputs l28imtwf, 〇c/c is the gain input signal. The variable attenuator is coupled to the amplifier for attenuating the gain input signal to generate an output signal. The signal detector is connected to the variable attenuator for detecting the output signal of the variable attenuator and outputting the control signal. Among them, when the input signal is larger, the control signal is larger, and the variable attenuator determines the attenuation of the input signal according to the control signal. The invention converts the first control signal proportional to the input signal into a second control signal which is inversely proportional to the input signal by using the inverting buffer, so that the input signal can be applied without changing the automatic gain control. It is proportional to the signal detector. Furthermore, the current required by the attenuator is provided by the inverting buffer, so sufficient current allows the attenuator to reach a greater dynamic range. In addition, the present invention uses a variable attenuator whose attenuation is proportional to the control signal, thereby eliminating the need for an inverting buffer and directly receiving a control signal proportional to the input signal to save cost. The above and other objects, features and advantages of the present invention will become more <RTIgt; [Embodiment] FIG. 2A is a block diagram of an automatic cup control circuit according to an embodiment of the invention. Referring to Fig. 2A, for convenience of explanation of the present invention, in the present embodiment, the automatic gain control circuit 2 is applied, for example, to a wireless transmission system. In different environments and conditions, the round-robin signal (Vin) obtained by the wireless transmission system is often unstable, so the automatic gain control circuit 200 is required to automatically change the system gain to generate a stable signal (ie, the round-out signal in the figure). Vout). 1281314 14572twf.doc/c The automatic gain control circuit 200 includes an amplifier 210 and an automatic attenuation circuit 220. The unstable input signal Vin is amplified (gained) by the amplifier 210 by a predetermined fixed ratio, and then outputted to the input signal 211. The automatic attenuation circuit 220 appropriately attenuates the input signal 211 of the gain according to the input signal size to generate a stable output signal Vout. . The automatic attenuation circuit 220 includes a variable attenuator 230, a signal detector 240, and an inverting buffer 250. The variable attenuator 230 attenuates the input signal 211 of the gain to produce an output signal Vout. The signal detector 240 detects the output signal Vout generated by the variable attenuator 230 to output a first control signal 241. The first control signal 241 is, for example, a voltage signal, and the first control signal 241 is coupled to the input signal vin. In direct proportion. The inverting buffer 250 inverts the first control signal 241 to output the second control signal 251. The voltage of the second control signal 251 is, for example, X_nV, where v represents the voltage of the first control signal 241, and n represents the voltage to be changed. The control override factor of v, X represents the highest voltage that the variable attenuator 230 can control. When the input signal is weakest, the attenuation of the attenuator is also the least, and the signal detection 240 output is Vmin, and X=nVmin, then n=x/vmin can be obtained. In other words, the second control signal 251 is inversely proportional to the input signal vin. Therefore, the variable attenuator 230 whose signal attenuation amount is inversely proportional to the control voltage can be applied to determine the signal attenuation amount according to the second control signal 251. Figure 2B is an exemplary circuit diagram of the automatic gain control circuit 2A of Figure 2A. The variable attenuator 230 is implemented, for example, by the conventional variable attenuator 120 of Fig. 1A, and therefore will not be described herein. The signal detector 24 is composed of, for example, a microstrip 1281314 14572 twf.doc/c line (microstrip line) 242, a diode 243, and a capacitor 244. The nickname detection 240 receives the output signal Vout via one end of the microstrip line 242, and the other end of the microstrip line 242 is coupled to the anode of the diode 243. One end of the capacitor 244 is coupled to the cathode of the diode 243, and the other end is grounded. The signal of the cathode of the diode 243 is the first control signal 241. Therefore, the voltage of the first control signal 241 will increase as the input signal vin increases, and vice versa as the input signal Vin decreases. The inverting buffer 250 is composed of, for example, a variable resistor 252, a resistor 253, and a pNp transistor 254. The variable resistor 252 has a first terminal & a second terminal b and a sliding end c for determining the resistance R2 and the sliding end c to the second between the first terminal a and the sliding end c according to the position of the sliding end c. The resistance between terminals b is R3. The first terminal & of the variable resistor 252 receives the first control signal 241. One end of the resistor 253 is coupled to the second terminal of the variable resistor 252, b' and the other end of the resistor 253 is lightly connected to the first voltage line (here, for example, a power supply voltage line). The resistor 253 acts here as a current limiting resistor, which affects the control range of the reducer. The larger the resistance R1 of the resistor 253, the more the attenuation dynamic range will be A, but the phase draw current will be larger: therefore, a balance point must be selected. The base of the transistor 254, the sliding end c of the snubber 252, the emitter is coupled to the first terminal b of the variable resistor, and the collector outputs the second control signal 251. The resistors R2 and R3 at the both ends of the above-mentioned reciprocal resistor 252 are offset amounts of the photographic magnification coefficient η and the attenuation value. If the value of the variable resistance is ', the initial attenuation (the initial value of the attenuator) will increase and the control rate η will increase. When S R2+R3 selects a smaller value, the initial attenuation and the control magnification factor are lower in 1281314 14572twf.doc/c. Secondly, the ratio of 2 and ^^ = is taken. If R2 increases and R3 decreases, the initial attenuation 虿 is increased and the control magnification factor n is reduced. Conversely, if R2 decreases and R3 increases, the initial attenuation is reduced and the control override factor n is increased. The ratio of the total value of R2 and R3 to the initial value of the individual attenuation value and the control magnification factor η is not the same, so the appropriate value must be selected according to different conditions. If the circuit needs to be adjusted frequently, the inverting buffer can be implemented with a variable resistor 252 as shown in Figure 2A. If the circuit is used under fixed conditions, the resistance values R2 and R3 can be implemented with a fixed resistor to reduce the circuit cost. As shown in Fig. 2C, the figure is another example circuit diagram of the inverting buffer 250 in the automatic gain control circuit 200 of Fig. 2. In the above embodiment, the conventional variable attenuator whose attenuation amount is inversely proportional to the control voltage (as shown in FIG. 1A) is used, so when the control signal outputted by the signal detector is proportional to the input signal, it needs to be reversed. The phase buffer is crying to adjust the control signal. Another embodiment will be described below using a variable attenuator whose attenuation is proportional to the control voltage, so that the signal detector whose output control is proportional to the input signal can be used to eliminate the inverting buffer and cut costs. FIG. 3 is a block diagram of another automatic gain control circuit according to an embodiment of the invention. Referring to FIG. 3A, the automatic gain control circuit 300 includes an amplifier 310 and an automatic attenuation circuit 320. The input signal 311 is outputted by the amplifier 31 放大 by amplifying (gaining) the unstable input signal Vin by a predetermined fixed magnification, and then the automatic attenuation circuit 320 appropriately attenuates the input signal 311 of the gain according to the input signal size to generate a stable output signal. 12 i28imc
Vout。其中，自動衰減電路320包括可變衰減器33〇與訊 號偵測器340。訊號侧器340戶斤輸出之控制訊號341係 與輸入afU虎成正比，其實施方式例如與前述實施例中圖2B 之訊號偵測器240相同。 可變衰減器330中，第一射頻阻流器(RF ch〇ke) 331 之第一端接收控制訊號341。第二射頻阻流器332之第一 端耦接至第一射頻阻流器331之第一端。第一二極體D1 之陰極耦接至射頻阻流器331之第二端，並且二極體D1 之陽極耦接至第二二極體D2之陽極。二極體D2之陰極 耦接至射頻阻流器332之第二端。第三射頻阻流器333之 第一端耦接至第一電壓線(例如為電源電壓線），以及射頻 阻流器333之第二端耦接二極體D1與D2之陽極。於本 實施例中，射頻阻流器333例如以電感與電阻串接而成。 弟二一極體D3之陽極搞接至二極體di之陰極，並 且第四二極體D4之陽極耦接至二極體D2之陰極。第一 %阻334之弟一端麵接至二極體D3之陰極，電阻334之 第一端耦接至第二電壓線。於本實施例中，第二電壓線例 如為接地線。第二電阻337之第一端耦接至二極體D4之 陰極，電阻337之第二端耦接至第二電壓線。第一電容335 之苐一知麵接至二極體D3之陰極，電容335之第-端輕 接至第二電壓線。第二電容336之第一端耦接至二極體 之陰極，電容336之第二端耦接至第二電壓線。第三電容 338之苐一端柄接至二極體D1之陰極，電容％8之第一 端接收放大後之輸入訊號311。第四電容339之第一端輕 13 1281314 , 14572twf.doc/c 接至二極體D2之陰極，電容339之第二端之訊號為輸出 訊號Vout。為了避免雜訊影響，更可在接收控制訊號之 處耦接電容 對於二極體D1〜D4而言，當導通電流越大則其高頻 阻抗越低；反之，當導通電流越小則其高頻阻抗越高。當 控制訊號341電位升高，則二極體D1與D2之電流減小 並且二極體D3與D4之電流增加，也就是二極體D1與 D2之阻抗增加並且二極體D3與D4之阻抗減少，此時相 當於可變哀減器330的衰減量增加。反之，當控制訊號341 電位降低，則二極體D1與D2之電流增加並且二極體D3 與D4之電流減少，也就是二極體D1與D2之阻抗變小 並且二極體D3與D4之阻抗變大，此時相當於可變衰減 器的衰減量減少。因此，可變衰減器33〇之衰減量將 隨著控制訊號升高而變大，如圖3所示。 〜雖然本發明已以三個實施例揭露如上，然其並非用以 IT =本I月，任何^習此技藝者，在不脫離本發明之精神 和範圍内’當可作些許之更動與潤飾，因 範圍當視後附之中請專利範圍所界定者為準。 μ 【圖式簡單說明】 圖1Α是傳統自動增益控制電路方塊圖。 關係^。出是圖1Α中可變衰減11之衰減量與控制訊號之 之一實施例所繪示之一種自動增 圖2A是依照本發明 分控制電路方塊圖。 14 Ι2813Α4— 圖2Β是圖2Α之自動增益控制電路的範例電路圖。 圖2C是圖2Α自動增益控制電路中反相緩衝器的另 一範例電路圖。 圖3Α是依照本發明之一實施例所繪示之另一種自動 增益控制電路方塊圖。 圖3Β是圖3Α中可變衰減器之衰減量與控制訊號之 關係圖。 【主要元件符號說明】 100 :傳統自動增益控制電路 110、 210、310 :放大器 111、 211、311 :被放大的輸入訊號 120 :可變衰減器 130 :所產生之控制訊號與輸入訊號成反比之訊號摘 測器 131、 242 :微帶線(microstrip line) 132、 243、D1 〜D4 :二極體 133、 244、335、336、338、339、361 :電容 200、300:自動增益控制電路 220、320 :自動衰減電路 230、330 ··可變衰減器 240、 340 :所產生之控制訊號與輸入訊號成正比之訊 號偵測器 241、 251、341 ··控制訊號 250 :反相缓衝器 15 252 :可變電阻 253、334、337 :電阻 254 :電晶體 331、332、333 ··射頻阻流器(RF choke) Vcon :控制訊號 Vin :輸入訊號 Vout :輸出訊號 16Vout. The automatic attenuation circuit 320 includes a variable attenuator 33A and a signal detector 340. The control signal 341 of the signal side device 340 is proportional to the input afU, and its implementation is the same as the signal detector 240 of FIG. 2B in the foregoing embodiment. In the variable attenuator 330, the first end of the first RF blocker (RF ch〇ke) 331 receives the control signal 341. The first end of the second RF block 332 is coupled to the first end of the first RF block 331. The cathode of the first diode D1 is coupled to the second end of the RF block 331, and the anode of the diode D1 is coupled to the anode of the second diode D2. The cathode of the diode D2 is coupled to the second end of the RF block 332. The first end of the third RF choke 333 is coupled to the first voltage line (eg, the power voltage line), and the second end of the RF block 333 is coupled to the anodes of the diodes D1 and D2. In this embodiment, the RF block 333 is formed by, for example, connecting an inductor and a resistor in series. The anode of the dipole D3 is connected to the cathode of the diode di, and the anode of the fourth diode D4 is coupled to the cathode of the diode D2. The first end of the first resistor 334 is connected to the cathode of the diode D3, and the first end of the resistor 334 is coupled to the second voltage line. In this embodiment, the second voltage line is, for example, a ground line. The first end of the second resistor 337 is coupled to the cathode of the diode D4, and the second end of the resistor 337 is coupled to the second voltage line. The first capacitor 335 is connected to the cathode of the diode D3, and the first end of the capacitor 335 is connected to the second voltage line. The first end of the second capacitor 336 is coupled to the cathode of the diode, and the second end of the capacitor 336 is coupled to the second voltage line. The first end of the third capacitor 338 is connected to the cathode of the diode D1, and the first end of the capacitor %8 receives the amplified input signal 311. The first end of the fourth capacitor 339 is light 13 1281314, 14572 twf.doc/c is connected to the cathode of the diode D2, and the signal of the second end of the capacitor 339 is the output signal Vout. In order to avoid the influence of noise, it is also possible to couple the capacitor at the place where the control signal is received. For the diodes D1 to D4, the higher the on-current is, the lower the high-frequency impedance is. On the contrary, the smaller the on-current is, the higher. The higher the frequency impedance. When the potential of the control signal 341 rises, the currents of the diodes D1 and D2 decrease and the currents of the diodes D3 and D4 increase, that is, the impedances of the diodes D1 and D2 increase and the impedances of the diodes D3 and D4 increase. The decrease is equivalent to an increase in the amount of attenuation of the variable attenuator 330. Conversely, when the potential of the control signal 341 is lowered, the currents of the diodes D1 and D2 increase and the currents of the diodes D3 and D4 decrease, that is, the impedances of the diodes D1 and D2 become smaller and the diodes D3 and D4 are smaller. The impedance becomes large, and the amount of attenuation corresponding to the variable attenuator is reduced at this time. Therefore, the amount of attenuation of the variable attenuator 33 变 will become larger as the control signal rises, as shown in FIG. </ RTI> Although the present invention has been disclosed in the above three embodiments, it is not intended to be used by IT = this month, and any person skilled in the art can make some changes and refinements without departing from the spirit and scope of the present invention. The scope of the patent is subject to the scope of the patent. μ [Simple description of the diagram] Figure 1 is a block diagram of a conventional automatic gain control circuit. Relationship ^. An automatic increase is shown in an embodiment of the attenuation of the variable attenuation 11 and the control signal in FIG. 1A. FIG. 2A is a block diagram of a control circuit in accordance with the present invention. 14 Ι2813Α4— Figure 2Β is an example circuit diagram of the automatic gain control circuit of Figure 2. Figure 2C is another exemplary circuit diagram of the inverting buffer of the Figure 2 automatic gain control circuit. FIG. 3 is a block diagram of another automatic gain control circuit according to an embodiment of the invention. Figure 3Β is a plot of the attenuation of the variable attenuator in Figure 3Α versus the control signal. [Main component symbol description] 100: conventional automatic gain control circuit 110, 210, 310: amplifier 111, 211, 311: amplified input signal 120: variable attenuator 130: the generated control signal is inversely proportional to the input signal Signal extractors 131, 242: microstrip lines 132, 243, D1 to D4: diodes 133, 244, 335, 336, 338, 339, 361: capacitors 200, 300: automatic gain control circuit 220 320: automatic attenuation circuit 230, 330 · variable attenuator 240, 340: the generated control signal is proportional to the input signal signal detector 241, 251, 341 · · control signal 250: inverting buffer 15 252 : Variable resistors 253, 334, 337 : Resistor 254 : Transistor 331 , 332 , 333 · · RF choke Vcon : Control signal Vin : Input signal Vout : Output signal 16