Integrated circuit and optical receiver

Abstract

The integrated circuit (50) comprises: an amplifier (1) which amplifies a current signal from an external light-receiving element (9) and converts it into a voltage signal; and a low-pass filter (10) which performs filtering processing on a bias voltage (Vbias) applied to the light-receiving element (9). The low-pass filter (10) comprises a resistor (2) and a capacitor series body (3), wherein the capacitor series body (3) is formed by connecting a plurality of capacitor elements (4) in series. One end of the resistor (2) of the low-pass filter (10) is connected to a power supply terminal (7b) to which a bias voltage (Vbias) is input, and the other end is connected to an input end of the capacitor series body (3) and a bias application electrode of the light-receiving element (9) to which a bias voltage is applied. The capacitor series body (3) of the low-pass filter (10) is configured such that the connection end between the two capacitor elements (4) connected in series and the output end of the capacitor series body (3) are each connected to a capacitor terminal (6), and the capacitor terminal (6) is selectively connected to a ground potential which serves as a reference for the bias voltage (Vbias).

Description

Technical Field

[0001] The present application relates to an integrated circuit having an external capacitive element for a light receiving element. Background Art

[0002] In optical communication, a transimpedance amplifier is used to amplify a weak current signal received by a light-receiving element such as a photodiode and convert it into a voltage signal. In an integrated circuit formed with such a transimpedance amplifier for optical communication, there is an integrated circuit equipped with a low-pass filter for removing the noise of the bias voltage of the photodiode (for example, patent document 1, non-patent document 1). The low-pass filter carried by the integrated circuit formed with the transimpedance amplifier and the photodiode connected to the integrated circuit are connected and used as shown in Figures 15 and 18 of non-patent document 1. When using a low-pass filter carried by an integrated circuit formed with a transimpedance amplifier, since the low-pass filter can be arranged at a position close to the light-receiving element, the low-pass filter carried by the integrated circuit is easy to use as a noise removal filter.

[0003] An example of connecting an avalanche photodiode to a transimpedance amplifier is shown in Fig. 16 and Fig. 17 of Non-Patent Document 1. In Non-Patent Document 1, the anode of the avalanche photodiode is connected to an external capacitor element instead of an internal capacitor element.

[0004] Patent Document 1: Japanese Patent Publication No. 2008-507943 ( Figure 4 )

[0005] Non-Patent Document 1: 11.3Gbps Limiting Transimpedance Amplifier with RSSI Data Sheet, Texas Instruments, August 2011 (Figures 15 to 18) Summary of the invention

[0006] The withstand voltage of the capacitor element in the low-pass filter mounted on the integrated circuit with the transimpedance amplifier is determined by the semiconductor manufacturing process of the integrated circuit. Therefore, even if the capacitor element mounted on the integrated circuit with the transimpedance amplifier can be used at the bias voltage of the photodiode of about several volts, it is not suitable for the bias voltage of the avalanche photodiode reaching 20 to 30 volts.

[0007] The technology disclosed in this specification is a technology for obtaining an integrated circuit equipped with a low-pass filter that can be applied to both the bias voltage of a photodiode and an avalanche photodiode.

[0008] An integrated circuit of an example disclosed in this specification is formed on a semiconductor substrate and converts a current signal input from an external light-receiving element into a voltage signal. The integrated circuit has: an amplifier, which amplifies the current signal from the light-receiving element and converts it into a voltage signal; and a low-pass filter, which filters the bias voltage applied to the light-receiving element. The low-pass filter has a resistor and a capacitor series body, which is formed by connecting a plurality of capacitor elements in series. One end of the resistor of the low-pass filter is connected to a power supply terminal to which a bias voltage is input, and the other end is connected to an input end of the capacitor series body and a bias application electrode of the light-receiving element to which a bias voltage is applied. The capacitor series body of the low-pass filter is constructed such that the connection end between the two capacitor elements connected in series and the output end of the capacitor series body are each connected to a capacitor terminal, and the capacitor terminal is selectively connected to a ground potential that serves as a reference for the bias voltage.

[0009] Effects of the Invention

[0010] An integrated circuit of an example disclosed in this specification can change the capacitance value of a mounted low-pass filter, and thus can be applied to both the bias voltage of a photodiode and an avalanche photodiode. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a diagram showing the circuit configuration of an optical receiver and an integrated circuit according to Embodiment 1.

[0012] Figure 2 yes Figure 1 A cross-sectional view of a capacitor element.

[0013] Figure 3 Yes means Figure 1 FIG. 1 is a diagram of an example of a first capacitance value change of an integrated circuit.

[0014] Figure 4 Yes means Figure 1 FIG. 1 is a diagram showing an example of changing the second capacitance value of an integrated circuit.

[0015] Figure 5 This is a diagram showing the circuit configuration of an optical receiver and an integrated circuit according to the second embodiment.

[0016] Figure 6 Yes means Figure 5 FIG. 1 is a diagram showing an example of changing the capacitance value of an integrated circuit. DETAILED DESCRIPTION

[0017] Implementation method 1.

[0018] Figure 1 This is a diagram showing the circuit configuration of an optical receiver and an integrated circuit according to Embodiment 1. Figure 2 yes Figure 1A cross-sectional view of a capacitor element. An optical receiver 60 that receives an optical signal transmitted by an optical fiber has: a light receiving element 9 that receives the optical signal and outputs a current signal; and an integrated circuit 50 that converts the current signal input from the light receiving element 9 into a voltage signal. The integrated circuit 50 has: a transimpedance amplifier (TIA) 1 that amplifies the weak current signal received by the light receiving element 9 and converts it into a voltage signal; a low-pass filter 10 that performs filtering to remove noise of the bias voltage Vbias supplied to the light receiving element 9; power supply terminals 7a, 7b, 7c; light receiving element connection terminals 5a, 5b that are connected to the light receiving element 9; a plurality of capacitor terminals 6a, 6b, 6c to 6n; and an output terminal 8. The low-pass filter 10 has a resistor 2 and a capacitor series body 3, which is formed by connecting a plurality of capacitor elements 4a, 4b, 4c, 4d to 4n in series. A light receiving element connection terminal 5a is connected to the connection point between the resistor 2 and the series input end which is one end of the capacitor series body 3, and each connection point of the capacitor element of the capacitor series body 3 and the series output end which is the other end of the capacitor series body 3 are connected to the capacitor terminals 6a, 6b, 6c to 6n respectively. One end of the resistor 2 is connected to the power supply terminal 7b, and the other end is connected to the series input end of the capacitor series body 3, wherein the power supply terminal 7b is connected to the power supply 11b. The light receiving element 9 is, for example, an avalanche photodiode (APD). The anode of the light receiving element 9 is connected to the transimpedance amplifier 1 via the light receiving element connection terminal 5b. The cathode (bias application electrode) of the light receiving element 9 is connected to the low-pass filter 10 via the light receiving element connection terminal 5a, that is, connected to the connection point between the resistor 2 and the series input end of the capacitor series body 3 of the low-pass filter 10.

[0019] The transimpedance amplifier 1 is supplied with a ground potential (GND potential) as a reference potential from the power supply terminal 7c, and is supplied with a voltage Vcc from the power supply 11a connected to the power supply terminal 7a. The transimpedance amplifier 1 amplifies the weak current signal of the light receiving element 9 input through the light receiving element connection terminal 5b, and outputs the output signal after converting it into a voltage signal from the output terminal 8. Figure 1 , an example is shown in which capacitor elements 4a, 4b, 4c, 4d to 4n are connected in series in order of distance from the cathode of the light receiving element 9 from near to far. One end of capacitor element 4a is connected to the cathode side of the light receiving element 9, and the other end is connected to capacitor element 4b and capacitor terminal 6a. Both ends of capacitor element 4b and subsequent capacitor elements are connected to capacitor terminals. Both ends of capacitor element 4b are connected to capacitor terminals 6a and 6b, and both ends of capacitor element 4c are connected to capacitor terminals 6b and 6c. Figure 1In the figure, the capacitor element between capacitor element 4d and capacitor element 4n, and the capacitor terminal between capacitor terminal 6c and capacitor terminal 6n are omitted. In addition, the number of the capacitor element is 4 when it is generally referred to, and 4a, 4b, 4c, 4d to 4n are used when they are distinguished. The number of the capacitor terminal is 6 when it is generally referred to, and 6a, 6b, 6c to 6n are used when they are distinguished.

[0020] The integrated circuit 50 is formed on the semiconductor substrate 21. The light receiving element connection terminals 5a, 5b, the capacitor terminals 6a, 6b, 6c to 6n, the power supply terminals 7a, 7b, 7c, and the output terminal 8 are, for example, wire bonding pads connected to wires. In addition, the light receiving element 9 can be an avalanche photodiode or a PIN type photodiode.

[0021] The capacitor element 4 is, for example, a MIM (Metal Insulator Metal) capacitor. Figure 2 A MIM (Metal Insulator Metal) type capacitor, i.e., a capacitor element 4, is shown. The capacitor element 4 is formed above a semiconductor substrate 21 on which a transimpedance amplifier 1 is formed. The capacitor element 4 has a first electrode 22, a second electrode 23, and an insulating film 24 formed between the first electrode 22 and the second electrode 23, and the capacitor element 4 is insulated from other capacitor elements 4, the resistor 2, the transimpedance amplifier 1, etc. by an insulating film 25. The withstand voltage of the capacitor element 4 formed by a semiconductor manufacturing process such as a MIM capacitor is determined by the semiconductor manufacturing process of the integrated circuit 50. In embodiment 1, by connecting a plurality of capacitor elements 4 in series, the effective voltage value applied to a single capacitor element 4 is reduced. In addition, the capacitance value and withstand voltage of the capacitor series body 3 of the low-pass filter 10 can be arbitrarily changed by selecting a capacitor terminal 6 connected to a ground potential (GND potential), i.e., grounded.

[0022] use Figure 3 , Figure 4 , an example of setting the capacitance value of the capacitor series body 3 is described. Figure 3 Yes means Figure 1 FIG. 1 is a diagram showing an example of a first capacitance value change of an integrated circuit, Figure 4 Yes means Figure 1 For example, regarding capacitor elements 4a, 4b, 4c, 4d to 4n, consider the case where all the capacitance values ​​are C [F] and the withstand voltage is Vrs [V]. Figure 3As shown in FIG. 1 , if only the capacitor terminal 6n connected to the capacitor element 4n is grounded, the capacitance value of the capacitor series body 3 becomes C / n[F], and the withstand voltage of the capacitor series body 3 becomes nVrs[V]. Therefore, the bias voltage Vbias applied to the capacitor series body 3 can be applied to n times the withstand voltage of one capacitor element 4. Figure 4 As shown, if only the capacitor terminal 6a connected to the capacitor element 4a and the capacitor element 4b is grounded, the capacitance value of the capacitor series body 3 becomes C [F], and the withstand voltage of the capacitor series body 3 becomes Vrs [V]. In addition, the capacitance value of the capacitor element 4 is not limited to the same value, and can also include different capacitance values.

[0023] The integrated circuit 50 of the first embodiment uses a plurality of capacitor elements 4 formed by a semiconductor manufacturing process of a conventional semiconductor integrated circuit with a withstand voltage of about several V, and obtains a low-pass filter 10 that can be applied to the bias voltage of an avalanche photodiode of 20 to 30 V. In addition, the integrated circuit 50 of the first embodiment can switch the grounding capacitor terminal 6, such as a wire bonding pad, by wire bonding, so that the low-pass filter 10 with the optimal capacitance value and withstand voltage can be used for the photodiode and the avalanche photodiode in the same integrated circuit.

[0024] As described above, the integrated circuit 50 of the first embodiment is formed on the semiconductor substrate 21, and is an integrated circuit that converts the current signal input from the external light receiving element 9 into a voltage signal. The integrated circuit 50 has: an amplifier (transimpedance amplifier 1), which amplifies the current signal from the light receiving element 9 and converts it into a voltage signal; and a low-pass filter 10, which performs filtering on the bias voltage Vbias applied to the light receiving element 9. The low-pass filter 10 has a resistor 2 and a capacitor series body 3, and the capacitor series body 3 is formed by connecting a plurality of capacitor elements 4 in series. One end of the resistor 2 of the low-pass filter 10 is connected to the power supply terminal 7b to which the bias voltage Vbias is input, and the other end is connected to the input end of the capacitor series body 3 and the bias application electrode (cathode) of the light receiving element 9 to which the bias voltage Vbias is applied. The connection end between the two capacitor elements 4 connected in series of the capacitor series body 3 of the low-pass filter 10 and the output end are each connected to the capacitor terminal 6, and the capacitor terminal 6 is selectively connected to the ground potential (GND potential) that serves as the reference of the bias voltage Vbias. The integrated circuit 50 of the first embodiment can change the capacitance value of the low-pass filter 10 with the above-mentioned structure, and is therefore applicable to both the bias voltage of a photodiode and an avalanche photodiode, and can be applied to both a photodiode and an avalanche photodiode as the light receiving element 9 .

[0025] The optical receiver 60 of the first embodiment includes: a light receiving element 9 that receives a light signal; and an integrated circuit 50 that converts a current signal input from the light receiving element 9 into a voltage signal. The integrated circuit 50 is formed on a semiconductor substrate 21, and includes: an amplifier (transimpedance amplifier 1) that amplifies the current signal from the light receiving element 9 and converts it into a voltage signal; and a low-pass filter 10 that performs filtering processing on the bias voltage Vbias applied to the light receiving element 9. The low-pass filter 10 includes a resistor 2 and a capacitor series body 3, and the capacitor series body 3 is formed by connecting a plurality of capacitor elements 4 in series. One end of the resistor 2 of the low-pass filter 10 is connected to a power supply terminal 7b to which the bias voltage Vbias is input, and the other end is connected to the input end of the capacitor series body 3 and the bias application electrode (cathode) of the light receiving element 9 to which the bias voltage Vbias is applied. The connection end between the two capacitor elements 4 connected in series of the capacitor series body 3 of the low-pass filter 10 and the output end are each connected to the capacitor terminal 6, and the capacitor terminal 6 is selectively connected to the ground potential (GND potential) that serves as the reference of the bias voltage Vbias. The optical receiver 60 of the first embodiment can change the capacitance value of the low-pass filter 10 carried by the above-mentioned structure, so it can be applied to both the bias voltage of the photodiode and the avalanche photodiode, and as the light receiving element 9, it can be applied to both the photodiode and the avalanche photodiode.

[0026] Implementation method 2.

[0027] Figure 5 is a diagram showing the circuit structure of an optical receiver and an integrated circuit according to Embodiment 2. Figure 6 Yes means Figure 5 The optical receiver 60 and the integrated circuit 50 of the second embodiment differ from the integrated circuit 50 of the first embodiment in that the end of the capacitor element 4n located at the farthest position from the cathode of the light receiving element 9 that is not connected to other capacitor elements 4, that is, the output end of the series capacitor 3 is always grounded. For example, the output end of the series capacitor 3 is always grounded through a through hole or the like.

[0028] The integrated circuit 50 of the second embodiment replaces the capacitor terminal 6n connected to the output terminal of the series capacitor 3 in the first embodiment with a through hole, thereby reducing the area corresponding to one capacitor terminal, for example, the area corresponding to one wire bonding pad, and omitting the wire bonding process. The integrated circuit 50 of the second embodiment has no electrical influence even if the capacitor terminal 6 connected to the connection point of the two capacitor elements 4 other than the output terminal of the series capacitor 3 is grounded. In addition, in Figure 5 , Figure 6 , showing the deletion Figure 1Although the example of the capacitor terminal 6n is shown, the capacitor terminal 6n may be provided and the capacitor terminal 6n may be always grounded through a through hole, etc. In this case, the wire bonding process for grounding the capacitor terminal 6n can be omitted.

[0029] use Figure 5 , Figure 6 , an example of setting the capacitance value of the capacitor series body 3 is described. For example, regarding the capacitor elements 4a, 4b, 4c, 4d to 4n, consider the case where the capacitance values ​​are all C [F] and the withstand voltage is Vrs [V]. Figure 5 As shown in FIG. 1 , when only one end of capacitor element 4n, i.e., the output end of the series capacitor body 3, is grounded, the capacitance value of the series capacitor body 3 becomes C / n[F], and the withstand voltage of the series capacitor body 3 becomes nVrs[V]. Therefore, the bias voltage Vbias applied to the series capacitor body 3 can be applied up to n times the withstand voltage of one capacitor element 4. In addition, if Figure 6 As shown, when the capacitor terminal 6a connected to the capacitor element 4a and the capacitor element 4b is grounded, the capacitance value of the capacitor series body 3 becomes C [F], and the withstand voltage of the capacitor series body 3 becomes Vrs [V]. In addition, the capacitance value of the capacitor element 4 is not limited to the same value, and can also include different capacitance values.

[0030] The integrated circuit 50 of embodiment 2 is similar to the integrated circuit 50 of embodiment 1. The capacitance value of the low-pass filter 10 carried therein can be changed, and it can be applicable to both the bias voltage of the photodiode and the avalanche photodiode. As the light receiving element 9, it can be applicable to both the photodiode and the avalanche photodiode.

[0031] As described above, the integrated circuit 50 of the second embodiment is an integrated circuit formed on the semiconductor substrate 21, and converts the current signal input from the external light receiving element 9 into a voltage signal. The integrated circuit 50 has: an amplifier (transimpedance amplifier 1), which amplifies the current signal from the light receiving element 9 and converts it into a voltage signal; and a low-pass filter 10, which performs filtering on the bias voltage Vbias applied to the light receiving element 9. The low-pass filter 10 has a resistor 2 and a capacitor series body 3, and the capacitor series body 3 is formed by connecting a plurality of capacitor elements 4 in series. One end of the resistor 2 of the low-pass filter 10 is connected to the power supply terminal 7b to which the bias voltage Vbias is input, and the other end is connected to the input end of the capacitor series body 3 and the bias application electrode (cathode) of the light receiving element 9 to which the bias voltage Vbias is applied. The capacitor series body 3 of the low-pass filter 10 is configured such that the connection ends between the two capacitor elements 4 connected in series are each connected to the capacitor terminal 6, and the output end is fixed to the ground potential (GND potential), wherein the capacitor terminal 6 is selectively connected to the ground potential (GND potential) that serves as the reference of the bias voltage Vbias. The integrated circuit 50 of the second embodiment can change the capacitance value of the low-pass filter 10 carried by the above-mentioned structure, so it can be applied to both the bias voltage of the photodiode and the avalanche photodiode, and as the light receiving element 9, it can be applied to both the photodiode and the avalanche photodiode.

[0032] The optical receiver 60 of the second embodiment includes: a light receiving element 9 that receives a light signal; and an integrated circuit 50 that converts a current signal input from the light receiving element 9 into a voltage signal. The integrated circuit 50 is formed on a semiconductor substrate 21, and includes: an amplifier (transimpedance amplifier 1) that amplifies the current signal from the light receiving element 9 and converts it into a voltage signal; and a low-pass filter 10 that performs filtering processing on the bias voltage Vbias applied to the light receiving element 9. The low-pass filter 10 includes a resistor 2 and a capacitor series body 3, and the capacitor series body 3 is formed by connecting a plurality of capacitor elements 4 in series. One end of the resistor 2 of the low-pass filter 10 is connected to a power supply terminal 7b to which the bias voltage Vbias is input, and the other end is connected to the input end of the capacitor series body 3 and the bias application electrode (cathode) of the light receiving element 9 to which the bias voltage Vbias is applied. The capacitor series body 3 of the low-pass filter 10 is configured such that the connection ends between the two capacitor elements 4 connected in series are each connected to the capacitor terminal 6, and the output end is fixed to the ground potential (GND potential), wherein the capacitor terminal 6 is selectively connected to the ground potential (GND potential) that serves as the reference of the bias voltage Vbias. The optical receiver 60 of the second embodiment can change the capacitance value of the low-pass filter 10 mounted thereon by the above-mentioned structure, and can therefore be applied to both the bias voltage of a photodiode and an avalanche photodiode, and as the light receiving element 9, can be applied to both a photodiode and an avalanche photodiode.

[0033] Furthermore, the capacitor element 4 is not limited to one capacitor element, and may be divided into a plurality of capacitor elements. In addition, the various embodiments may be freely combined within a range that does not contradict each other, and the various embodiments may be appropriately modified or omitted.

[0034] Description of the label

[0035] 1…transimpedance amplifier, 2…resistor, 3…capacitor series body, 4, 4a, 4b, 4c, 4d, 4n…capacitor element, 6, 6a, 6b, 6c, 6n…capacitor terminal, 7a, 7b, 7c…power supply terminal, 9…light receiving element, 10…low-pass filter, 21…semiconductor substrate, 50…integrated circuit, 60…optical receiver, Vbias…bias voltage.

Claims

1. An integrated circuit formed on a semiconductor substrate, which converts a current signal input from an external light-receiving element into a voltage signal, The integrated circuit is characterized by having: an amplifier that amplifies the current signal from the light receiving element and converts it into the voltage signal; and a low-pass filter for filtering the bias voltage applied to the light-receiving element, The low-pass filter has a resistor and a capacitor series body, and the capacitor series body is formed by connecting a plurality of capacitor elements in series. One end of the resistor is connected to a power supply terminal to which the bias voltage is input, and the other end is connected to an input end of the capacitor series body and a bias application electrode of the light receiving element to which the bias voltage is applied. The capacitor series body is configured such that a connection end between two capacitor elements connected in series and an output end of the capacitor series body are each connected to a capacitor terminal, and the capacitor terminal is selectively connected to a ground potential that serves as a reference for the bias voltage. The capacitor terminals are wire bonding pads formed on the integrated circuit.

2. The integrated circuit according to claim 1, characterized in that The capacitive element is a MIM type capacitor.

3. An integrated circuit formed on a semiconductor substrate, which converts a current signal input from an external light-receiving element into a voltage signal, The integrated circuit is characterized by having: an amplifier that amplifies the current signal from the light receiving element and converts it into the voltage signal; and a low-pass filter for filtering the bias voltage applied to the light-receiving element, The low-pass filter has a resistor and a capacitor series body, and the capacitor series body is formed by connecting a plurality of capacitor elements in series. One end of the resistor is connected to a power supply terminal to which the bias voltage is input, and the other end is connected to an input end of the capacitor series body and a bias application electrode of the light receiving element to which the bias voltage is applied. The capacitor series body is configured such that the connection ends between the two capacitor elements connected in series are each connected to a capacitor terminal, and the output end of the capacitor series body is fixed to the ground potential, wherein: The capacitor terminal is selectively connected to the ground potential serving as a reference for the bias voltage.

4. The integrated circuit according to claim 3, characterized in that The capacitor terminals are wire bonding pads formed on the integrated circuit.

5. The integrated circuit according to claim 3 or 4, characterized in that: The capacitive element is a MIM type capacitor. 6 . An optical receiver comprising: a light receiving element that receives a light signal; and the integrated circuit according to claim 1 , which converts a current signal input from the light receiving element into a voltage signal.

7. The optical receiver according to claim 6, characterized in that When the light receiving element is an avalanche photodiode, the capacitor terminal on the output end side of the capacitor series body is connected to the ground potential.

8. The optical receiver according to claim 6, characterized in that When the light receiving element is a photodiode having a bias voltage lower than that of an avalanche photodiode, the capacitor terminal on the input end side of the capacitor series body is connected to the ground potential. 9 . An optical receiver comprising: a light receiving element that receives a light signal; and the integrated circuit according to claim 3 , which converts a current signal input from the light receiving element into a voltage signal.

10. The optical receiver according to claim 9, characterized in that When the light receiving element is a photodiode having a bias voltage lower than that of an avalanche photodiode, the capacitor terminal on the input end side of the capacitor series body is connected to the ground potential.

11. An optical receiver comprising: a light receiving element that receives a light signal; and the integrated circuit according to claim 3 that converts a current signal input from the light receiving element into a voltage signal. The optical receiver is characterized in that When the light receiving element is an avalanche photodiode, all of the capacitor terminals are not connected to the ground potential.

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