Single-phase differential conversion circuit

Abstract

A single-phase differential conversion circuit (10) according to the present invention includes a differential amplifier (11) including a positive phase circuit (111) that processes a positive phase signal and a negative phase circuit (112) that processes a negative phase signal and a transmission line (12) connected to an output end (111_2) of the positive phase circuit (11). The transmission line (12) rotates the phase of the positive phase signal to reduce the intensity of the positive phase signal. Another differential amplifier (21) may be connected to the downstream side of the differential amplifier (11).　With this configuration, the single-phase differential conversion circuit according to the present invention can provide excellent differential characteristics.

Description

Technical Field

[0001] The present invention relates to a single-phase differential conversion circuit in which a transmission line is connected to a differential amplifier.

Background Art

[0002] In a high-speed optical communication system, a single-phase differential conversion circuit for a baseband signal is required to have good differential characteristics, that is, a small 180° phase difference and intensity mismatch between differential signals.

[0003] As a technique for converting a single-phase baseband signal into a differential baseband signal, as shown in FIG. 10, a technique using a differential amplifier 71 is disclosed (Non-Patent Document 1). In this technique, a signal is input to a terminal In on one side (positive-phase circuit side) of the differential amplifier 71, and the other terminal (inverting circuit side) is fixed to a common bias (Vb), whereby a differential signal is obtained at the output terminals (OutP, OutN). Hereinafter, the OutP side (In side) is referred to as the positive-phase circuit side, and the OutN side (Vb side) is referred to as the inverting circuit side.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the conventional single-phase differential conversion circuit, there is a problem that the differential characteristics deteriorate at high frequencies. Fig. 11 shows a schematic diagram of a conventional single-phase differential conversion circuit (differential amplifier 71). As shown in Fig. 11, as the signal becomes high-frequency, the impedance of the parasitic capacitance 72 of the transistor decreases. As a result, the phase of the signal on the positive-phase circuit side rotates via the parasitic capacitance 72 and is added to the signal on the negative-phase circuit side. Therefore, in the conventional single-phase differential conversion circuit, the differential characteristics deteriorate at high frequencies.

[0006] Specifically, when the signal is at low frequency, since the impedance of the parasitic capacitance 72 is high, the signal is blocked.

[0007] On the other hand, when the signal is at high frequency, the impedance of the parasitic capacitance 72 decreases, and the signal flows into the signal on the negative-phase circuit side (arrow 73 in the figure). This signal rotates in phase during propagation and is added to the signal of the opposite phase. Also, the signal strength on the negative-phase circuit side is reduced.

[0008] In this way, when the signal is at high frequency, the impedance of the parasitic capacitance 72 decreases, and the positive-phase signal affects the negative-phase signal.

[0009] Figs. 12A and B show the simulation results of the differential characteristics of the conventional single-phase differential conversion circuit. As shown in Fig. 12A, the mismatch of the 180° phase difference is 22° at 140 GHz. Also, as shown in Fig. 12B, the mismatch of the intensity is 3.5 dB at 140 GHz. Thus, in the conventional single-phase differential conversion circuit, the differential characteristics deteriorate at high frequencies.

Means for Solving the Problem

[0010] In order to solve the problems as described above, the single-phase differential conversion circuit according to the present invention includes a differential amplifier composed of a positive-phase circuit that processes a positive-phase signal and a negative-phase circuit that processes a negative-phase signal, and a First transmission line , a second transmission line connected to the output terminal of the inverting circuit and connected to the output terminal of the positive-phase circuit, the first transmission line is longer than the second transmission line, said First transmission line being characterized by rotating the phase of the positive-phase signal and reducing the intensity of the positive-phase signal.

[0011] In addition, the single-phase differential conversion circuit according to the present invention includes a differential amplifier composed of a positive-phase circuit that processes a positive-phase signal and a negative-phase circuit that processes a negative-phase signal, and a compensation circuit. The compensation circuit includes a resistor, an inductor connected in series, and a capacitor connected in parallel at an output terminal of the positive-phase circuit.

Advantages of the Invention

[0012] According to the present invention, a single-phase differential conversion circuit having good differential characteristics can be provided.

Brief Description of the Drawings

[0013]

Figure 1A

Figure 1B

Figure 2A

Figure 2B

Figure 3

Figure 4A

Figure 4B

Figure 5

Figure 6A

Figure 6B

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12A

Figure 12B

Embodiments for Carrying Out the Invention

[0014] <First Embodiment> The single-phase differential conversion circuit according to the first embodiment of the present invention will be described with reference to FIGS. 1A to 2B.

[0015] <Configuration of Single-Phase Differential Conversion Circuit> As shown in FIGS. 1A and 1B, the single-phase differential conversion circuit 10 according to the present embodiment includes a differential amplifier 11 and a transmission line 12. A tail current source 13 may also be provided.

[0016] The differential amplifier 11 is composed of a circuit (hereinafter referred to as the "positive-phase circuit") 111 for processing a positive-phase signal and a circuit (hereinafter referred to as the "inverse-phase circuit") 112 for processing an inverse-phase signal, and includes an input terminal 111_1 and an output terminal 111_2 of the positive-phase circuit 111, and an input terminal 112_1 and an output terminal 112_2 of the inverse-phase circuit 112.

[0017] The single-phase differential conversion circuit 10 includes an input terminal In and an output terminal OutP on the positive-phase circuit 111 side, and a terminal Vb connected to the common-mode voltage and an output terminal OutN on the negative-phase circuit 112 side.

[0018] The transmission line 12 is connected between the output end 111_2 of the positive-phase circuit 111 of the differential amplifier 11 and the output terminal OutP on the positive-phase circuit 111 side.

[0019] In the single-phase differential conversion circuit 10, since a transmission line is also connected to the wiring on the negative-phase circuit 112 side (not shown), the transmission line 12 connected to the positive-phase circuit 111 side may be longer than the transmission line on the negative-phase circuit 112 side.

[0020] The transmission line 12 can correct a 180° phase difference mismatch by additionally rotating the phase of the output signal on the positive-phase circuit 111 side with respect to the output signal on the negative-phase circuit 112 side. Also, since the signal strength on the positive-phase circuit 111 side is reduced by the transmission line 12, an intensity mismatch can be corrected with respect to the negative-phase circuit 112 side.

[0021] <Effect of the single-phase differential conversion circuit> Figures 2A and B respectively show the simulation results of the differential characteristics in the single-phase differential conversion circuit 10 according to the present embodiment (solid lines in the figures). For reference, the simulation results of the differential characteristics in a conventional single-phase differential conversion circuit are also shown (dotted lines in the figures).

[0022] The calculations were performed using "Advanced Design System" (manufacturer: Keysight Technologies, Inc.). In the calculations, the phase and intensity of the input sine wave defined by the frequency component were set, and the amount of phase to be rotated in the transmission line 12 was set. Here, the amount of phase to be rotated in the transmission line 12 was set to 13 degrees.

[0023] In the conventional single-phase differential conversion circuit, at frequencies of 0 to 140 GHz, the 180° phase difference mismatch is 22°, and the intensity difference mismatch is 3.5 dB.

[0024] On the other hand, in the single-ended differential conversion circuit 10 according to the present embodiment, the frequency is 0 to 140 GHz, the mismatch of the 180° phase difference is 9°, and the mismatch of the intensity difference is 1.8 dB. Thus, compared with the conventional single-ended differential conversion circuit, both the mismatch of the phase difference and the mismatch of the intensity difference are reduced and improved.

[0025] Here, the ideal phase difference characteristic is that the phase difference is constant at 180 degrees, that is, the mismatch of the 180° phase difference is 0°. However, it is only necessary to reduce the mismatch of the 180° phase difference within a predetermined range. For example, it is sufficient if it can be reduced to about 10% or less of 180 degrees.

[0026] Generally, the mismatch of the 180° phase difference of the differential amplifier 11 becomes maximum at the highest frequency of the desired band (for example, 140 GHz in FIG. 2). By using the transmission line 12 having a phase rotation amount equivalent to the amount of the mismatch of the phase difference, the mismatch of the phase difference can be improved to the maximum extent.

[0027] According to the single-ended differential conversion circuit according to the present embodiment, both the mismatch of the phase difference and the mismatch of the intensity difference are achieved, and good differential characteristics can be obtained.

[0028] <Second Embodiment> The single-ended differential conversion circuit according to the second embodiment of the present invention will be described with reference to FIGS. 3 to 4B.

[0029] <Configuration of Single-Ended Differential Conversion Circuit> As shown in FIG. 3, the single-ended differential conversion circuit 20 according to the present embodiment includes two differential amplifiers 11 and 21, and a transmission line 12 connected between the output terminal 111_2 of the positive-phase circuit 111 of the front-stage differential amplifier 11 and the input terminal 211_1 of the positive-phase circuit 211 of the rear-stage differential amplifier 21 among the two differential amplifiers 11 and 21.

[0030] In other words, another differential amplifier 21 is connected to the rear stage of the single-ended differential conversion circuit 10 according to the first embodiment.

[0031] The differential amplifier 21 in the latter stage can remove the common mode, thus improving the differential characteristics of the single-ended differential conversion circuit 20.

[0032] <Effect of single-ended differential conversion circuit> Figs. 4A and 4B respectively show the simulation results of the differential characteristics in the single-ended differential conversion circuit 20 according to this embodiment (the solid line in the figure). For reference, the simulation results of the differential characteristics in a conventional single-ended differential conversion circuit, that is, a single-ended differential conversion circuit composed of two-stage differential amplifiers 11 and 21 without a transmission line, are also shown (the dotted line in the figure).

[0033] In the conventional single-ended differential conversion circuit, at frequencies from 0 to 140 GHz, the mismatch of the 180° phase difference is 9°, and the mismatch of the intensity difference is 1 dB.

[0034] On the other hand, in the single-ended differential conversion circuit 20 according to this embodiment, at frequencies from 0 to 140 GHz, the mismatch of the 180° phase difference is 1°, and the mismatch of the intensity difference is 0.3 dB. Thus, compared with the conventional single-ended differential conversion circuit, both the mismatch of the phase difference and the mismatch of the intensity difference are reduced and improved.

[0035] According to the single-ended differential conversion circuit according to this embodiment, both the mismatch of the phase difference and the mismatch of the intensity difference are achieved, and good differential characteristics can be obtained.

[0036] In this embodiment, an example using a two-stage differential amplifier is shown, but it is not limited thereto. A three-stage or more differential amplifier may be used, and the differential characteristics can be further improved.

[0037] <The third embodiment> The single-ended differential conversion circuit according to the third embodiment of the present invention will be described with reference to Fig. 5.

[0038] As shown in Fig. 5, the single-ended differential conversion circuit 30 according to this embodiment includes two differential amplifiers 11 and 21, and two transmission lines 12 and 22.

[0039] The two transmission lines 12 and 22 are respectively connected between the output terminal 111_2 of the positive-phase circuit 111 of the front-stage differential amplifier 11 and the input terminal 211_1 of the positive-phase circuit 211 of the rear-stage differential amplifier 21, and between the output terminal 211_2 of the positive-phase circuit 211 of the rear-stage differential amplifier 21 and the output terminal OutP on the positive-phase circuit side of the single-ended differential conversion circuit 30.

[0040] This increases the degree of freedom in the design parameters of the single-ended differential conversion circuit and further improves the differential characteristics.

[0041] According to the single-ended differential conversion circuit according to this embodiment, both the phase difference mismatch and the intensity difference mismatch are achieved, increasing the degree of freedom in the design parameters and further obtaining good differential characteristics.

[0042] <Fourth Embodiment> The single-ended differential conversion circuit according to the fourth embodiment of the present invention will be described with reference to FIGS. 6A and 6B.

[0043] As shown in FIG. 6A, the single-ended differential conversion circuit 40 according to this embodiment includes two differential amplifiers 11 and 21, and two transmission lines 31_1 and 32_1.

[0044] The two transmission lines 31_1 and 32_1 are respectively connected between the output terminal 111_2 of the positive-phase circuit 111 of the front-stage differential amplifier 11 and the input terminal 211_1 of the positive-phase circuit 211 of the rear-stage differential amplifier 21, and between the output terminal 212_2 of the inverting-phase circuit 212 of the rear-stage differential amplifier 21 and the output terminal OutN on the inverting-phase circuit side of the single-ended differential conversion circuit 40.

[0045] Alternatively, as shown in FIG. 6B, the two transmission lines 31_2 and 32_2 may be respectively connected between the output terminal 112_2 of the inverting-phase circuit 112 of the differential amplifier 11 and the input terminal 212_1 of the inverting-phase circuit 212 of the rear-stage differential amplifier 21, and between the output terminal 211_2 of the positive-phase circuit 211 of the rear-stage differential amplifier 21 and the output terminal OutP on the positive-phase circuit side of the single-ended differential conversion circuit 40_2.

[0046] According to the single-phase differential conversion circuit according to this embodiment, when peaking, ripple, or the like occurs in the frequency characteristics of the single-phase differential conversion circuit, this peaking, ripple, or the like can be suppressed, and the differential characteristics can be further improved.

[0047] Also, in the single-phase differential conversion circuits 40 and 40_2, the change in the phase difference between the differential amplifiers is more sensitive to the transmission lines 31_2 and 32_1 connected to the output terminal of the subsequent differential amplifier 21 than to the transmission lines 31_1 and 32_2 connected to the output terminal of the differential amplifier 11.

[0048] Therefore, by making the lengths of the transmission lines 31_1 and 32_2 connected to the output terminal of the previous differential amplifier longer than those of the transmission lines 31_2 and 32_1 connected to the output terminal of the subsequent differential amplifier, the sensitivity in the single-phase differential conversion circuit 40 can be reduced, and the influence of manufacturing variations can be reduced.

[0049] <Modification Example 1> The single-phase differential conversion circuit according to this modification example includes a distributed amplifier designed with distributed constants instead of the differential amplifiers in the single-phase differential conversion circuits according to the first to fourth embodiments. Thereby, the characteristics of the single-phase differential conversion circuit can be broadened.

[0050] Here, by matching the characteristic impedance of the transmission line in the single-phase differential conversion circuit with the input / output impedance of the distributed amplifier (usually 50 Ω), the frequency ripple can be reduced.

[0051] <Fifth Embodiment> The single-phase differential conversion circuit according to the fifth embodiment of the present invention includes a compensation circuit 51 instead of the transmission lines in the single-phase differential conversion circuits according to the first to fourth embodiments.

[0052] The compensation circuit 51 is composed of lumped constant elements. For example, as shown in FIG. 7, it is composed of a resistor 52, an inductor 53, and a capacitor 54. For example, in the compensation circuit 51, the resistor 52 and the inductor 53 are connected in series to the output terminal of the positive-phase circuit of the differential amplifier of the single-phase differential conversion circuit, and the capacitor 54 is connected in parallel.

[0053] Alternatively, as shown in FIG. 8, the transmission line 55, the resistor 52, and the inductor 53 may be connected in series, and the capacitor 54 may be connected in parallel. Here, the transmission line 55 may be shorter than the transmission lines used in the first to fourth embodiments.

[0054] Thereby, while improving the differential characteristics, the area of the single-phase differential conversion circuit can be reduced, and the degree of freedom in design can be improved.

[0055] <Sixth Embodiment> The single-phase differential conversion circuit according to the sixth embodiment of the present invention will be described with reference to FIG. 9.

[0056] The single-phase differential conversion circuit 60 according to the present embodiment includes, as shown in FIG. 9, a differential amplifier 61, a compensation circuit 62, a detection circuit 63, and a control circuit 64.

[0057] The compensation circuit 62 is connected to the output terminal of the positive-phase circuit of the differential amplifier 61, the variable resistor 621 and the inductor 622 are connected in series, and the variable capacitor 623 is connected in parallel.

[0058] The detection circuit 63 is connected to the output terminals OutP and OutN of the single-phase differential conversion circuit, and detects the intensity difference and the phase difference between the differential signals of the positive-phase signal and the negative-phase signal.

[0059] The control circuit 64 has an output connected to the variable resistor 621 and the variable capacitor 623 of the compensation circuit 62, and generates a control voltage of the variable resistor 621 so that the intensity difference between the differential signals input from the detection circuit 63 is reduced.

[0060] Further, the control circuit 64 generates a control voltage of the variable capacitor 623 so that the phase difference between the differential signals input from the detection circuit 63 becomes equal to or less than a predetermined value. Here, the predetermined value may be, for example, about 10% of 180 degrees.

[0061] The control circuit 64 applies these control voltages to the variable resistor 621 and the variable capacitor 623.

[0062] According to the single-phase differential conversion circuit according to this embodiment, by detecting the intensity difference and phase difference between differential signals generated in the differential amplifier and performing feedback control, the differential characteristics can be automatically controlled. As a result, the phase difference mismatch and intensity difference mismatch can be reduced, and the differential characteristics can be improved.

[0063] Instead of the differential amplifier in the single-phase differential conversion circuit according to the fifth and sixth embodiments, a distributed amplifier designed with a distributed constant may be provided.

[0064] In the embodiments of the present invention, in the configuration, manufacturing method, etc. of the single-phase differential conversion circuit, an example of the structure, dimensions, material, etc. of each component is shown, but it is not limited thereto. Any structure that can exhibit the function of the single-phase differential conversion circuit and achieve the effects may be used.

Industrial Applicability

[0065] The present invention relates to a single-phase differential conversion circuit and can be applied to a high-speed optical communication system.

Explanation of Reference Numerals

[0066] 10 Single-phase differential conversion circuit 11 Differential amplifier 111 Positive-phase circuit 111_1 Input terminal of the positive-phase circuit 111_2 Output terminal of the positive-phase circuit 112 Inverse-phase circuit 12 Transmission line

Claims

1. A differential amplifier comprising a positive-phase circuit for processing a positive-phase signal and a negative-phase circuit for processing a negative-phase signal, a first transmission line connected to the output terminal of the positive-phase circuit, and a second transmission line connected to the output terminal of the negative-phase circuit and characterized in that the first transmission line is longer than the second transmission line, and the first transmission line rotates the phase of the positive-phase signal and reduces the intensity of the positive-phase signal a single-phase differential conversion circuit.

2. Another differential amplifier is connected to the subsequent stage of the differential amplifier The single-phase differential conversion circuit according to claim 1, characterized in that.

3. Another transmission line is connected to either the output terminal of the positive-phase circuit or the output terminal of the negative-phase circuit in the other differential amplifier The single-phase differential conversion circuit according to claim 2, characterized in that.

4. Another differential amplifier is connected to the preceding stage of the differential amplifier, and another transmission line is connected to the output terminal of the negative-phase circuit in the other differential amplifier The single-phase differential conversion circuit according to claim 1, characterized in that.

5. A differential amplifier comprising a positive-phase circuit for processing a positive-phase signal and a negative-phase circuit for processing a negative-phase signal, and a compensation circuit and characterized in that the compensation circuit includes a resistor and an inductor connected in series to the output terminal of the positive-phase circuit, and a capacitor connected in parallel a single-phase differential conversion circuit.

6. The compensation circuit further includes a transmission line connected in series The single-phase differential conversion circuit according to claim 5, characterized in that.

7. The single-phase differential conversion circuit according to claim 5 or claim 6, a detection circuit connected to the terminal on the positive-phase circuit side and the terminal on the negative-phase circuit side in the single-phase differential conversion circuit; a control circuit connected to the output of the detection circuit and connected to the resistor and the capacitor and comprising: wherein the resistor is a variable resistor, the capacitor is a variable capacitor, the detection circuit detects a differential signal between the positive-phase signal and the negative-phase signal, and detects an intensity difference and a phase difference between the differential signals, the control circuit applies a voltage to the resistor so that the intensity difference is reduced, and applies a voltage to the capacitor so that the phase difference becomes equal to or less than a predetermined value A single-phase differential conversion circuit characterized by the above.

8. The differential amplifier is a distributed amplifier The single-phase differential conversion circuit according to any one of claims 1 to 7, characterized by the above.

9. The differential amplifier includes a tail current source The single-phase differential conversion circuit according to any one of claims 1 to 8, characterized by the above.

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