Abstract:
A high-frequency circuit is provided, which makes it possible to prevent degradation of its high-frequency characteristic even if the lengths of bonding wires used are not decreased. This circuit includes: (a) an electronic element having a capacitance; (b) a signal line for transmitting a high-frequency electric signal to the element; (c) a terminating resistor for impedance matching; (d) a first bonding wire for electrically connecting the signal line and the element; and (e) a second bonding wire for electrically connecting the element and the resistor. A characteristic impedance of combination of the element and the first and second bonding wires is equal to or greater than that of input side of the electric signal with respect to the combination. An inductance of the second wire is greater than that of the first wire. Preferably, at least one of the lengths of the first and second bonding wires is decreased, which enhances the advantage of the high-frequency circuit.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a communication apparatus or device such as an optical communication apparatus/device (e.g., a light source or an optical transmitter) and a radio communication apparatus/device (e.g., a portable phone), and more particularly, to a High-Frequency (HF) circuit to be mounted on a communication apparatus/device of this type that prevents its HF characteristic from degrading, and a module equipped therewith. 
     2. Description of the Related Art 
     With optical communications systems, signal light is generated by direct or indirect modulation method of the output light of a semiconductor laser as a light source according to a signal to be transmitted in the transmission side. Then, the signal light thus generated is sent to an optical detector in the reception side by way of a medium. 
     In the direct modulation method of light, a semiconductor laser itself is driven with an intensity- or frequency-modulated current according to a signal to be transmitted, thereby generating the signal light. On the other hand, in the indirect modulation method of light, a semiconductor laser is driven with a dc current to generate output light with a constant intensity and then, the output light thus generated is modulated by an intensity-, frequency-, or phase-modulation method with an external modulator according to a signal to be transmitted, thereby generating the signal light. 
     As known well, when the bit rate of information is in the order of gigabits per second (i.e., Gb/sec) or higher, the transmittable distance is limited due to wavelength chirping occurring in the direct modulation method. Therefore, the indirect modulation method of light is used for transmission at such the high bit rate as above. 
     It is usual that an external modulator is formed in the form of module. For example, only an external modulator is formed as a module. Alternately, an external modulator and a light source (e.g., a semiconductor laser) are combined together to form a module, which is termed the “modulator-integrated light source” module. 
     In recent years, the bit rate of information or data to be transmitted has been becoming higher (e.g., Gb/sec or higher). Therefore, to transmit the information from the transmission side to the reception side without any errors, there is the increasing need to improve the high-frequency characteristics of the external modulator. To meet this need, various improved modules of this type have been developed and disclosed. 
     FIGS. 1 and 2 show the configuration of an example of the prior-art modulator-integrated light source modules. As seen from these figures, on a conductive base  101 , a dielectric substrate  102  and a heat sink  103  are formed to be apart from each other at a small distance. The dielectric substrate  102  is, for example, made of alumina (Al 2 O 3 ). The sink  103  is made of material with high thermal conductivity. 
     A modulator-integrated light source chip  120  is mounted on the sink  103 , where the chip  120  comprises a semiconductor laser  109  and an external modulator  110 . The sink  103  serves to cool the chip  120 , i.e., to dissipate the heat generated by the chip  120 . The sink  103  is mechanically and electrically connected to the base  101  by way of a conductive via hole  111   b.    
     On the surface of the dielectric substrate  102 , a patterned conductive layer is deposited, forming a strip-shaped signal line  107  and two ground lines  108   a  and  108   b  at each side of the signal line  107 . The surface of the substrate  102  is exposed from the lines  107 ,  108   a  and  108   b  through two elongated windows. The signal line  107  and the ground lines  108   a  and  108   b  constitute a coplanar-type transmission line. The ground lines  108   a  and  108   b  are mechanically and electrically connected to the base  101  by way of conductive via holes  111   a . The signal line  107  is not electrically connected to the base  101 . 
     A matching resistor  104 , which serves as a terminator for impedance matching, is formed on the exposed surface of the dielectric layer  102  between the signal line  107  and the ground line  108   b . The resistor  104  is located near the end of the signal line  107 , which is in the vicinity of the heat sink  103 . The two ends of the resistor  104  are mechanically and electrically connected to the lines  107  and  108   b , respectively. The resistor  104  is of the chip type or thin-film type. 
     The signal line  107  is electrically connected to the heat sink  103  by way of a conductive bonding wire  105 . One end of the wire  105  is bonded to the nearer end of the line  107  to the sink  103 . The other end of the wire  105  is bonded to the sink  103  at its nearest edge to the line  107 . The heat sink  103  is electrically connected to the external modulator  110  of the chip  120  by way of a conductive bonding wire  106 . One end of the wire  106  is bonded to the sink  103  at its nearest edge to the line  107 . The other end of the wire  106  is bonded to the pad of the modulator  110  of the chip  120 . The laser  109  is supplied with an electric, driving current by way of a conductive bonding wire  112 . 
     A high-frequency electrical input signal S IN  to be transmitted is applied to the signal line  107  from its furthest end from the heat sink  103 . The signal S IN  is then sent to the external modulator  110  of the modulator-integrated light source chip  120  by way of the signal line  107 , the bonding wires  105  and  106 , and the sink  103 . The modulator  110  modulates the output light of the laser  109  according to the signal S IN  thus inputted, generating the signal light. The signal light thus generated is emitted from the chip  120  and the modulator-integrated light source module. 
     With the prior-art module shown in FIGS. 1 and 2, as described above, the external modulator  110  of the modulator-integrated light source chip  120  and the dielectric substrate  102  are located to be apart from each other at a specific small distance, thereby decreasing the lengths of the bonding wires  105  and  106 . Thus, the inductance components of the wires  105  and  106  are restricted, suppressing the degradation of the high-frequency characteristic of the modulator  110 . 
     However, it is often that the distance between the dielectric substrate  102  and the modulator-integrated light source chip  120  is unable or difficult to be short as desired due to requirements in designing the module of this type. In other words, the bonding wires  105  and  106  are often unable to be short as desired. As a result, there is a limit in the method of preventing degradation of the high-frequency characteristic of the module by decreasing the lengths of the bonding wires. It is preferred that this problem is solved by a different method if possible. 
     In addition, the Japanese Non-Examined Patent Publication No. 10-275957 published in 1998 discloses an optical semiconductor chip carrier. This carrier comprises the same technique as described above while a microstrip line is used as the transmission line for the input signal S IN  into the external modulator  110 . 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide a high-frequency circuit that makes it possible to prevent degradation of its high-frequency characteristic by a different method from the above-described method of decreasing the lengths of bonding wires used. 
     Another object of the present invention is to provide a high-frequency circuit module that makes it possible to prevent degradation of its high-frequency characteristic by a different method from the above-described method of decreasing the lengths of bonding wires used. 
     The above objects together with others not specifically mentioned will become clear to those skilled in the art from the following description. 
     According to a first aspect of she present invention, a high-frequency circuit is provided, which comprises: 
     (a) an electronic element having a capacitance; 
     (b) a signal line for transmitting a high-frequency electric signal to the element; 
     (c) a terminating resistor for impedance matching; 
     (d) a first bonding wire for electrically connecting the signal line and the element; and 
     (e) a second bonding wire for electrically connecting the element and the resistor; 
     wherein a characteristic impedance of combination of the element and the first and second bonding wires is equal to or greater than that of input side of the electric signal with respect to the combination; 
     and wherein an inductance of the second wire is greater than that of the first wire. 
     With the high-frequency circuit according to the first aspect of the present invention, the characteristic impedance of the combination of the electronic element and the first and second bonding wires is equal to or greater than the characteristic impedance of the input side of the high-frequency electric signal with respect to the combination. Also, The inductance of the second bonding wire is greater than the inductance of the first bonding wire. Therefore, the high-frequency characteristic of the high-frequency circuit according to the first aspect is prevented from degrading by the use of a different method from the above-described method of decreasing the lengths of the first and second bonding wires. 
     Needless to say, if at least one of the lengths of the first and second bonding wires is decreased, the above-described advantage of the circuit of the first aspect of the invention is enhanced. 
     In a preferred embodiment of the circuit according to the first aspect, the element has a conductive pad. The element and the first wire are electrically connected to each other at the pad while the element and the second wire are electrically connected to each other at the same pad. 
     In another preferred embodiment of the circuit according to the first aspect, the electronic element has a first conductive pad and a second conductive pad. The element and the first wire are electrically connected to each other at the first pad while the element and the second wire are connected to each other at the second pad. 
     In still another preferred embodiment of the circuit according to the first aspect, a conductive island electrically connected to the element by way of a third bonding wire is additionally provided. The signal line is electrically connected to the island by way of the first wire, thereby electrically connecting the signal line to the element by way of the first and third wires. The resistor is electrically connected to the island by way of the second wire, thereby electrically connecting the resistor to the element by way of the second and third wires. 
     In a further preferred embodiment of the circuit according to the first aspect, the element is a modulator for generating an electric or optical signal by modulation according to the electric signal transmitted through the signal line. 
     In a still further preferred embodiment of the circuit according to the first aspect, the inductance of the second wire is approximately twice in value the inductance of the first wire. 
     According to a second aspect of the present invention, a high-frequency circuit module is provided, which comprises a base and the high-frequency circuit according to the first aspect mounted on the base. 
     With the high-frequency circuit module according to the second aspect of the invention, the high-frequency circuit according to the first aspect is mounted on the base. Thus, there is the same advantage as that of the circuit of the first aspect. 
     In a preferred embodiment of the module according to the second aspect, the element is mounted on a heat sink fixed to the base and the signal line is located on a dielectric layer formed on the base. The resistor is fixed directly on the base. 
     In another preferred embodiment of the module according to the second aspect, the element is mounted on a heat sink fixed to the base and the signal line is located on a dielectric layer formed on the base. The resistor is fixed on the sink. 
     According to a third aspect of the present invention, a communication device is provided, which comprises the high-frequency circuit module according to the second aspect. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the present invention may be readily carried into effect, it will now be described with reference to the accompanying drawings. 
     FIG. 1 is a schematic plan view showing the internal configuration of a prior-art modulator-integrated light source module. 
     FIG. 2 is a schematic side view showing the internal configuration of the prior-art modulator-integrated light source module of FIG.  1 . 
     FIG. 3 is a schematic plan view showing the internal configuration of a modulator-integrated light source module according to a first embodiment of the invention. 
     FIG. 4 is a schematic side view showing the internal configuration of the modulator-integrated light source module according to the first embodiment of FIG.  3 . 
     FIG. 5 is a schematic plan view showing the internal configuration of a modulator-integrated light source module according to a second embodiment of the invention. 
     FIG. 6 is a schematic side view showing the internal configuration of the modulator-integrated light source module according to the second embodiment of FIG.  5 . 
     FIG. 7 is a schematic plan view showing the internal configuration of a modulator-integrated light source module according to a third embodiment of the invention. 
     FIG. 8 is a schematic side view showing the internal configuration of the modulator-integrated light source module according to the third embodiment of FIG.  7 . 
     FIG. 9 is a graph showing the frequency characteristic of the parameter S 11  of the module according to the first embodiment of FIG.  3 . 
     FIG. 10 is a graph showing the frequency characteristic of the parameter S 21  of the module according to the first embodiment of FIGS. 3 and 3. 
     FIG. 11 is a graph showing the variation of the parameters S 11  and S 21  of the module according to the first embodiment of FIGS. 3 and 4 as a function of the inductance of the bonding wire. 
     FIG. 12 is a graph showing the frequency characteristic of the parameter S 11  of the module according to the first embodiment of FIGS. 3 and 4 and the prior-art module of FIGS. 1 and 2. 
     FIG. 13 is a graph showing the frequency characteristic of the parameter S 21  of the module according to the first embodiment of FIGS. 3 and 4 and the prior-art module of FIGS.  1  and  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described in detail below while referring to the drawings attached. 
     FIRST EMBODIMENT 
     As shown in FIGS. 3 and 4, a high-frequency circuit module according to a first embodiment of the invention, which is a modulator-integrated light source module, comprises a block-shaped conductive base  1 , a dielectric substrate  2 , a heat sink  3 , a modulator-integrated light source chip  20 , and a matching resistor  4 . The substrate  2 , the sink  3 , and the resistor  4  are mounted on the surface of the base  1 . The substrate  2  and the resistor  4  are located at opposite sides to each other with respect to the sink  3 . The sink  3  is apart from the substrate  2  and the resistor  4  at small distances. The chip  20  is mounted on the sink  3 . The chip  20  comprises a semiconductor laser  9  and an external modulator  10 . The resistor  4  is of the chip type or thin-film type. 
     The dielectric substrate  2  is, for example, made of alumina (Al 2 O 3 ). The heat sink  3  serves to cool the modulator-integrated light source chip  20  mounted thereon, i.e., to dissipate the heat generated by the chip  20 . The sink  3  is mechanically and electrically connected to the base  1  by way of a conductive via hole (e.g., a plated via hole)  11   b.    
     On the surface of the dielectric substrate  2 , a patterned conductive layer is deposited, forming a strip-shaped signal line  7  and two ground lines  8   a  and  8   b  at each side of the line  7 . The surface of the substrate  2  is exposed from the lines  7 ,  8   a  and  8   b  through two elongated windows. The signal line  7  and the ground lines  8   a  and  8   b  constitute a coplanar-type transmission line. The ground lines  8   a  and  8   b  are electrically connected to the conductive base  1  by way of conductive via holes  11   a.  The signal line  7  is not electrically connected too the base  1 . 
     Instead of the coplanar-type transmission line formed by the lines  7 ,  8   a , and  8   b , any microstrip line may be used as the transmission line for the input signal S IN  into the external modulator  10 . 
     The matching resistor  4 , which serves as a terminator for impedance matching in the module, is mounted on the surface of the base  1  at the opposite side to the substrate  2  with respect to the sink  3 . One end or terminal  4   b  of the resistor  4  is electrically connected to the base  1  by way of a conductive via hole  11   c.    
     One end of a conductive bonding wire  5  is bonded to the near end of the signal line  7  while the other end thereof is bonded to a bonding pad  21  of the external modulator  10  of the chip  20 . Thus, the signal line  7  is electrically connected to the modulator  10  by way of the bonding wire  5 . 
     One end of a conductive bonding wire  6  is bonded to the bonding pad  21  of the modulator  10  of the chip  20  while the other end thereof is bonded to the other end or another terminal  4   a  of the resistor  4 . Thus, the modulator  10  is electrically connected to the resistor  4  by way of the bonding wire  6 . As described above, the terminal  4   b  of the resistor  4  is electrically connected to the base  11  by way of the via hole  11   c.    
     Thus, the signal line  7  is electrically connected to the external modulator  10  of the chip  20  by way of the bonding wire  5  and at the same time, the line  7  is electrically connected to the matching resistor  4  by way of the bonding wires  5  and  6  and the common bonding pad  21 . In other words, the modulator  10  and the resistor  4  are electrically connected in parallel to the line  7 . 
     A high-frequency electric input signal S IN  to be transmitted is applied to the signal line  7  from its opposite end to the heat sink  3 . The signal S IN  is then sent to the external modulator  10  of the modulator-integrated light source chip  20  by way of the signal line  7  and the bonding wire  5 . The modulator  10  modulates the output light of the laser  9  with a constant intensity according to the electric signal S IN  thus inputted, generating the signal light. The signal light thus generated is emitted from the chip  20  and the modulator-integrated light source module. 
     The length of the bonding wires  5  and  6  is so determined as to satisfy the following conditions (i) and (ii). 
     (i) The characteristic impedance of combination of the external modulator  10  of the modulator-integrated light source chip  20  and the bonding wires  5  and  6  is equal to or greater than the characteristic impedance of the input side of the high-frequency input signal S IN  with respect to the same combination, 
     (ii) The inductance of the bonding wire  6  is greater in value than the inductance of the bonding wire  5 . 
     The laser  9  is supplied with an electric, driving current by way of a conductive bonding wire  12 . 
     With the high-frequency circuit module (i.e., modulator-integrated light source module) according to the first embodiment of FIGS. 3 and 4, the characteristic impedance of the combination of the external modulator  10  of the modulator-integrated light source chip  20  and the bonding wires  5  and  6  is equal to or greater than the characteristic impedance of the input side of the high-frequency electric signal S IN  with respect to the same combination. Also, The inductance of the bonding wire  6  is greater in value than the inductance of the bonding wire  5 . Therefore, the degradation of the high-frequency characteristic of the high-frequency circuit module of the first embodiment is prevented by the use of a different method from the previously-described method of decreasing the lengths of the bonding wires  105  and  106  in the prior-art module. 
     FIGS. 9 and 10 show the frequency characteristic of the S parameters of the module according to the first embodiment of FIGS. 3 and 4, where the inductance L 2  of the bonding wire  6  was set at 0.2 nH, 0.6 nH, 1.0 nH, and 1.4 nH while the inductance L 1  of the bonding wire  5  was kept at 0.6 nH. 
     In FIG. 9, the parameter S 11  is shown, which indicates the high-frequency reflection characteristic of the module. As seen from FIG. 9, when the inductance L 2  of the wire  6  is 0.2 nH and 0.6 nH, which are equal to or less than the inductance L 1  (0.6 nH) of the wire  5 , the return loss exceeds −10 dB at the frequency of 10 GHz or higher. This means that the high-frequency reflection characteristic degrades at the frequency of 10 GHz or higher. On the other hand, when the inductance L 2  of the wire  6  is 1.0 nH and 1.4 nH, which are greater than the inductance L 1  (0.6 nH) of the wire  5 , the return loss does not exceed −10 dB. This means that the high-frequency reflection characteristic does not degrade. 
     Moreover, in FIG. 10, the parameter S 21  is shown, which indicates the frequency response characteristic of the module. As seen from FIG. 10, in the region where the value of S 21  is equal to −3 dB or lower, the curve of the inductance L 2  of the wire  6  approaches to a straight line when the inductance L 2  is less than the inductance L 1  (=0.6 nH). Unlike this, the curve of the inductance L 2  of the wire  6  is approximately kept the same when the inductance L 2  is equal to or greater than the inductance L 1  (=0.6 nH). 
     Accordingly, it is seen that the inductances L 1  and L 2  are preferably set to satisfy the relationship of L 1 ≦L 2 . To realize the relationship of L 1 ≦L 2 , for example, the length of the bonding wire  5  is set to be shorter than that of the bonding wire  6 . According to this condition, the length of the wire  5  is set at 0.6 mm and the length of the wire  6  is set at 1.0 mm in the module of the first embodiment. In this case, the value of S 11  at 10 GHz was −10 dB while the −3 dB region of S 21  was given at 15 GHz, as seen from FIGS. 9 and 10, respectively. 
     FIG. 11 shows the change of the −3 dB region of S 21  and the value of S 11  at 10 GHz as a function of the inductance L 2  of the wire  6 , where the inductance L 1  of the wire  5  is used as a parameter. 
     As seen from FIG. 11, the inductances L 1  and L 2  of the wires  5  and  6  are dependent on each other. It is also seen that if the relationship of L 1 ≦L 2  is satisfied, the −3 dB region of S 21  is held to be approximately equal to that of the impedance matched state while the degradation of the value of S 11  is effectively restrained. 
     Additionally, it is seen from FIG. 11 that if the relationship of L 1 ≦L 2  is satisfied, the high-frequency characteristic changes scarcely, even if the length of the wire  6  fluctuates due to unwanted positional shift in the mounting processes of the heat sink  3  and resistor  4  on the base  1  to thereby change the inductance L 2  of the wire  6 . This means that the tolerance of the parameter S 21  against the change or fluctuation of the length of the wire  6  is expanded. 
     Moreover, as seen from FIG. 11, when the length of the wires  5  and  6  are determined in such a way that the inductances L 1  and L 2  satisfy the relationship of 2×L 1 =L 2 , the value of S 11  is optimized. For example, when L 1 =0.4 nH and L 2 =0.8 nH, or L 1 =0.6 nH and L 2 =1.2 nH, or L 1 =0.8 nH and L 2 =1.6 nH, the value of S 11  is optimized. 
     Here, supposing that the external modulator  10  of the chip  20  has a capacitance C, the characteristic impedance Z of the LC transmission line formed by the capacitance C of the modulator  10  and the inductances L 1  and L 2  of the bonding wires  5  and  6  is given by the following equation (1).              Z   =         (     L1   -   L2     )     C               (   1   )                                
     If the characteristic impedance Z of the LC transmission line is equal to the characteristic impedance Z 0  of the input signal line  7 , the value of S 21  is maximized and the value of S 11  is minimized. However, in practical use, it is unnecessary that the value of S 21  is maximized and the value of S 11  is minimized. 
     FIGS. 12 and 13 show the frequency characteristic of the parameters S 11  and S 12  of the module according to the first embodiment of FIGS. 3 and 4 and the prior-art module of FIGS. 1 and 2, respectively. 
     As seen from FIGS. 12 and 13, in practical use, the value of S 21  may not be maximized even when the value of S 11  is minimized due to impedance mismatching. In this case, however, if the value of S 21  exceeds a specific reference value (e.g., 14 GHz in FIGS.  12  and  13 ), it is preferred that the value of S 11  is set as small as desired. 
     In the examples of FIGS. 12 and 13, Z is given as 50 Ω when L 1 =0.4 nH, L 2 =0.8 nH, and C=0.48 pF. Z is given as 61 Ω when L 1 =0.6 nH, L 2 =1.2 nH, and C=0.48 pF. Since Z 0  has a normal value of 50 Ω, the relationship of Z≧Z 0  is preferably satisfied. 
     The curves of the invention in FIGS. 12 and 13 were obtained when Z=Z 0 =50 Ω, L 1 =0.6 nH, and L 2 =1.4 nH in the module of the first embodiment while the curves of the prior-art module of FIGS. 1 and 2 were obtained when L 1 =0.3 nH, and L 2 =0.2 nH. As seen from these figures, the reflection characteristic S 11  and the frequency characteristic S 21  of the module of the first embodiment are improved by approximately 6 dB and approximately 2 GHz compared with those of the prior art module. 
     SECOND EMBODIMENT 
     FIGS. 5 and 6 show a high-frequency circuit module (a modulator-integrated light source module) according to a second embodiment of the invention, which comprises the same configuration as the module according to the first embodiment of FIGS. 3 and 4, except that the matching resistor  4  is located on the heat sink  3  near the signal line  7 , and that a bonding pad  22  is additionally formed on the modulator  10 . Therefore, the description about the same configuration is omitted here by attaching the same reference symbols as those in the first embodiment of FIGS. 3 and 4 for the sake of simplification of description in FIGS. 5 and 6. 
     In the module of the second embodiment, one end of the bonding wire  5  is bonded to the near end of the signal line  7  while the other end of the wire  5  is bonded to the bonding pad  21  of the external modulator  10  of the chip  20 . Thus, the signal line  7  is electrically connected to the modulator  10  by way of the bonding wire  5 . This is the same as the first embodiment. 
     Unlike this, one end of the bonding wire  6  is bonded to the bonding pad  22  (instead of the pad  21 ) of the modulator  10  of the chip  20  while the other end of the wire  6  is bonded to the terminal  4   a  of the resistor  4 . Thus, the modulator  10  is electrically connected to the resistor  4  by way of the bonding wire  6 . The other terminal  4   b  of the resistor  4  is electrically connected to the base  11  by way of a conductive via hole  11   d.    
     Thus, the signal line  7  is electrically connected to the matching resistor  4  by way of the bonding wires  5  and  6  and the bonding pads  21  and  22 . 
     With the high-frequency circuit module according to the second embodiment of FIGS. 5 and 6, because of the same reason as described in the first embodiment, the degradation of the high-frequency characteristic of the module is prevented even when the lengths of the bonding wires  5  and  6  are decreased. 
     There is an additional advantage that the possibility of double bonding of the bonding wires  5  and  6  onto the same pad  21 , which might occur in the first embodiment, is eliminated. 
     THIRD EMBODIMENT 
     FIGS. 7 and 8 show a high-frequency circuit module (a modulator-integrated light source module) according to a third embodiment of the invention, which comprises the same configuration as the module according to the first embodiment of FIGS. 3 and 4, except that a conductive island  16  is additionally formed on the heat sink  3 , and that the ends of the bonding wires  5  and  6  and an additional bonding wire  17  are commonly bonded to the island  16 . Therefore, the description about the same configuration is omitted here by attaching the same reference symbols as those in the first embodiment of FIGS. 3 and 4 for the sake of simplification of description in FIGS. 7 and 8. 
     In the module of the third embodiment, one end of the bonding wire  5  is bonded to the near end of the signal line  7  while the other end of the wire  5  is bonded to the island  16  of the sink  3 . One end of the bonding wire  17  is bonded to the same island  16  and the other end thereof is bonded to the bonding pad  21  of the modulator  10 . Thus, the signal line  7  is electrically connected to the modulator  10  by way of the bonding wires  5  and  17  and the island  16 . 
     One end of the bonding wire  6  is bonded to the same island  16  of the modulator  10  while the other end of the wire  6  is bonded to the terminal  4   a  of the resistor  4 . Thus, the modulator  10  is electrically connected to the resistor  4  by way of the bonding wires  17  and  6  and the island  16 . The other terminal  4   b  of the resistor  4  is electrically connected to the base  11  by way of the conductive via hole  11   c.    
     The signal line  7  is electrically connected to the matching resistor  4  by way of the bonding wires  5  and  6  and the island  16 . 
     With the high-frequency circuit module according to the third embodiment of FIGS. 7 and 8, because of the same reason as described in the first embodiment, the degradation of the high-frequency characteristic of the high-frequency circuit module is prevented even when the lengths of the bonding wires  5 ,  6  and  17  are decreased. 
     There is an additional advantage in the inspection of the fabrication process sequence of the module. Specifically, prior to the process of bonding the wire  6 , the optical and electrical characteristics of the external modulator  9  of the chip  20  can be tested. Therefore, according to the result of this test, the process of bonding the wire  6  is carried out for only the modules that have exhibited good test results. 
     VARIATIONS 
     Needless to say, the invention is not limited to the above-described first to third embodiments. For example, in the above-described embodiments, the invention is applied to the high-frequency circuit module for optical communication. However, the invention is applicable to any circuit or any module where a signal line for transmitting a high-frequency signal is electrically connected to an element having a capacitance by way of a bonding wire or wires and at the same time, the element is electrically connected to a matching resistor for impedance matching by way of another bonding wire or wires. 
     If the module of the invention is incorporated into a modulation section of an optical communication device or a electrical communication device (e.g., a portable phone), a communication device having excellent high-frequency characteristics is realized. 
     While the preferred forms of the present invention have been described, it is to be understood that modifications will be apparent to those skilled in the art without departing from the spirit of the invention. The scope of the present invention, therefore, is to be determined solely by the following claims.