Baseband amplifier

Abstract

This baseband amplifier comprises: a distributed amplifier (10); an RF amplifier (11); a demultiplexer (12) that outputs, to a first output terminal, a signal, from among input signals, that includes at least a signal component that is at least a high-frequency-side cutoff frequency of the distributed amplifier (10), and that outputs, from a second output terminal to the RF amplifier (11), a signal, from among input signals, that includes at least a signal component that is at least a low-frequency-side cutoff frequency of the RF amplifier (11); a group delay adjuster (14) that is inserted between the first output terminal of the demultiplexer (12) and the input terminal of the distributed amplifier (10); and a multiplexer (13) that multiplexes the output of the distributed amplifier (10) and the output of the RF amplifier (11).

Description

Baseband Amplifier

[0001] The present invention relates to a baseband amplifier.

[0002] Baseband amplifiers are essential components in various applications such as optical communications and measuring instruments. In recent years, the bandwidth required for baseband amplifiers has increased along with increases in communication capacity and higher speed measuring instruments. A distributed baseband amplifier as shown in FIG. 25 has been proposed as a configuration for realizing a wideband baseband amplifier (Non-Patent Document 1).

[0003] The distributed baseband amplifier is composed of an input transmission line CPW10 having an input end connected to an input terminal 1, an output transmission line CPW20 having an end connected to an output terminal 2, an input termination resistor R1 having one end connected to the end of the input transmission line CPW10 and the other end connected to ground, an output termination resistor R2 having one end connected to the input end of the output transmission line CPW20 and the other end connected to ground, and a plurality of unit cells 3 arranged along the input transmission line CPW10 and the output transmission line CPW20, having input terminals connected to the input transmission line CPW10 and output terminals connected to the output transmission line CPW20.

[0004] In a distributed baseband amplifier, in order to connect to external devices, the characteristic impedance of the input transmission line CPW10 is designed to be, for example, 50 Ω when the parasitic capacitance of the transistors constituting the unit cell 3 is incorporated. Furthermore, the characteristic impedance of the output transmission line CPW20 is designed to be, for example, 50 Ω when the parasitic capacitance of the transistors is incorporated. Hereinafter, a transmission line including the parasitic capacitance of the transistors will be referred to as a pseudo-transmission line to distinguish it from a normal transmission line. Furthermore, by matching the phase velocities of the input and output pseudo-transmission lines, it becomes possible to amplify wideband baseband signals including signal components from DC.

[0005] However, the bandwidth that can be achieved by a conventional distributed baseband amplifier is limited by the cutoff frequency of the artificial transmission line. Specifically, the bandwidth of a distributed baseband amplifier is approximately half the maximum oscillation frequency fmax of the transistors that make up the unit cell 3. Therefore, with conventional distributed baseband amplifiers, it has been difficult to achieve a bandwidth that significantly exceeds fmax / 2.

[0006] T. Jyo et al., “A 241-GHz-Bandwidth Distributed Amplifier with 10-dBm P1dB in 0.25-μm InP DHBT Technology”, 2019 IEEE MTT-S International Microwave Symposium (IMS), Boston, MA, USA, 2019, pp.1430-1433, doi:10.1109 / MWSYM.2019.8700975

[0007] The present invention has been made to solve the above problems, and has an object to provide a baseband amplifier having a wider bandwidth than conventional ones.

[0008] The baseband amplifier of the present invention is characterized by comprising: a distributed amplifier; an RF amplifier configured to have higher frequency pass characteristics than the distributed amplifier; a branching filter configured to output, from a first output terminal, a signal of an input signal that includes at least a signal component that is equal to or lower than a high-frequency cutoff frequency of the distributed amplifier, and to output, from a second output terminal, a signal of the input signal that includes at least a signal component that is equal to or higher than a low-frequency cutoff frequency of the RF amplifier, to the RF amplifier; a first group delay adjuster inserted between the first output terminal of the branching filter and an input terminal of the distributed amplifier; and a multiplexer configured to multiplex the signal amplified by the distributed amplifier and the signal amplified by the RF amplifier.

[0009] According to the present invention, by providing a distributed amplifier, an RF amplifier, a demultiplexer, and a multiplexer, it is possible to widen the bandwidth of the baseband amplifier to a band that greatly exceeds half the maximum oscillation frequency of the transistors that constitute the unit cells of the distributed amplifier and the RF amplifier. Also, in the present invention, by providing a first group delay adjuster, it is possible to improve the flatness of the group delay characteristics of the baseband amplifier.

[0010] FIG. 1 is a block diagram showing the configuration of a baseband amplifier according to a first embodiment of the present invention. FIG. 2A is a diagram showing the band of an input signal of the first embodiment of the present invention. FIG. 2B is a diagram showing the band of an output signal of a branching filter according to the first embodiment of the present invention. FIG. 2C is a diagram showing the band of an output signal of a branching filter according to the first embodiment of the present invention. FIG. 2D is a diagram showing the frequency characteristics of a distributed amplifier according to the first embodiment of the present invention. FIG. 2E is a diagram showing the frequency characteristics of an RF amplifier according to the first embodiment of the present invention. FIG. 3A is a diagram showing the band of an output signal of a distributed amplifier according to the first embodiment of the present invention. FIG. 3B is a diagram showing the band of an output signal of an RF amplifier according to the first embodiment of the present invention. FIG. 3C is a diagram showing the band of an output signal of a multiplexer according to the first embodiment of the present invention. FIG. 4 is a block diagram showing the configurations of a branching filter and a multiplexer according to the first embodiment of the present invention. FIG. 5 is a circuit diagram showing the configuration of a unit cell of a distributed amplifier according to the first embodiment of the present invention. FIG. 6 is a block diagram showing the configuration of an RF amplifier according to the first embodiment of the present invention. FIG. 7 is a circuit diagram showing the configuration of a unit cell of an RF amplifier according to the first embodiment of the present invention. FIG. 8 is a block diagram showing another configuration of a branching filter and a multiplexer according to the first embodiment of the present invention. FIG. 9 is a block diagram showing another configuration of a demultiplexer and a multiplexer according to the first embodiment of the present invention. FIG. 10 is a block diagram showing another configuration of a demultiplexer and a multiplexer according to the first embodiment of the present invention. FIG. 11 is a block diagram showing another configuration of a demultiplexer and a multiplexer according to the first embodiment of the present invention. FIG. 12 is a block diagram showing another configuration of a demultiplexer and a multiplexer according to the first embodiment of the present invention. FIG. 13 is a block diagram showing another configuration of a demultiplexer and a multiplexer according to the first embodiment of the present invention. FIG. 14 is a block diagram showing another configuration of a demultiplexer and a multiplexer according to the first embodiment of the present invention. FIG. 15 is a diagram showing the transmission characteristics of a baseband amplifier without a group delay adjuster. FIG. 16 is a diagram showing the group delay characteristics of a baseband amplifier without a group delay adjuster. FIG. 17 is a diagram showing an output waveform when a PAM4 signal is input to a baseband amplifier without a group delay adjuster. FIG. 18 is a diagram showing the transmission characteristics of a baseband amplifier according to the first embodiment of the present invention. FIG. 19 is a diagram showing the group delay characteristics of a baseband amplifier according to the first embodiment of the present invention.Fig. 20 is a diagram showing an output waveform when a PAM4 signal is input to a baseband amplifier according to a first embodiment of the present invention. Fig. 21 is a block diagram showing the configuration of a baseband amplifier according to a second embodiment of the present invention. Fig. 22 is a block diagram showing the configuration of a baseband amplifier according to a third embodiment of the present invention. Fig. 23 is a circuit diagram showing the configuration of a group delay adjuster of the baseband amplifier according to the first and second embodiments of the present invention. Fig. 24 is a circuit diagram showing the configuration of a group delay adjuster of the baseband amplifier according to a third embodiment of the present invention. Fig. 25 is a block diagram showing the configuration of a conventional distributed baseband amplifier.

[0011] [First Embodiment] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a baseband amplifier according to a first embodiment of the present invention. In the following description, the baseband amplifier will be abbreviated as a BB amplifier. The BB amplifier of this embodiment includes a distributed amplifier 10, an RF (Radio Frequency) amplifier 11 having a higher frequency pass characteristic than the distributed amplifier 10, a branching filter 12 that outputs to a first output terminal a signal of an input signal Vin that includes at least a signal component below the high-frequency cutoff frequency of the distributed amplifier 10 and outputs to a second output terminal a signal of the input signal Vin that includes at least a signal component above the low-frequency cutoff frequency of the RF amplifier 11, a multiplexer 13 that multiplexes the signal amplified by the distributed amplifier 10 and the signal amplified by the RF amplifier 11, a group delay adjuster 14 inserted between the first output terminal of the branching filter 12 and the input terminal of the distributed amplifier 10, and a group delay adjuster 15 inserted between the second output terminal of the branching filter 12 and the input terminal of the RF amplifier 11.

[0012] The splitter 12 splits a wideband input signal Vin as shown in FIG. 2A into two signals: a signal S1 having a band as shown in FIG. 2B and a signal S2 having a band as shown in FIG. 2C, and outputs the signal S1 to a first output terminal and the signal S2 to a second output terminal. The signal S1 may be a signal that includes at least a signal component below the high-frequency cutoff frequency of the distributed amplifier 10, and may also include a signal component above the high-frequency cutoff frequency. The signal S2 may be a signal that includes at least a signal component above the low-frequency cutoff frequency of the RF amplifier 11, and may also include a signal component below the low-frequency cutoff frequency. The characteristics of the group delay adjusters 14 and 15 will be described later.

[0013] The frequency characteristics of distributed amplifier 10 are shown in Figure 2D, and the frequency characteristics of RF amplifier 11 are shown in Figure 2E. Distributed amplifier 10 amplifies signal S1 and outputs signal S3 in the band shown in Figure 3A. RF amplifier 11 amplifies signal S2 and outputs signal S4 in the band shown in Figure 3B.

[0014] The multiplexer 13 multiplexes the signal S3 output from the distributed amplifier 10 and the signal S4 output from the RF amplifier 11. The bandwidth of the output signal Vout of the multiplexer 13 is shown in FIG. 3C. With the above configuration, in this embodiment, it is possible to widen the bandwidth of the BB amplifier to a bandwidth that greatly exceeds ½ of the fmax of the transistors that constitute the unit cells of the distributed amplifier 10.

[0015] Next, specific examples of the branching filter 12 and the multiplexer 13 will be described with reference to Figure 4. In this embodiment, directional couplers are used for both the branching filter 12 and the multiplexer 13. The reason for using directional couplers is that they facilitate the branching and multiplexing of wideband baseband signals that include signal components from DC. Furthermore, in order to maintain flatness in the gain of the entire BB amplifier, it is necessary to adjust the strength of the signals S2 and S4 on the RF amplifier 11 side. If directional couplers are used for the branching filter 12 and the multiplexer 13, it is possible to easily adjust the signal strength by adjusting the degree of coupling of the directional couplers.

[0016] The directional coupler 120 constituting the branching filter 12 is composed of a transmission line 121 arranged between the input port P11 and a transmission port P12, a transmission line 122 electromagnetically coupled to the transmission line 121, and a termination resistor R3 having one end connected to the end of the transmission line 122 opposite the coupled port P13 and the other end connected to ground. In the directional coupler 120, the input port P11 is connected to the input terminal of the BB amplifier, the transmission port P12 is connected to the input terminal of the group delay adjuster 14, and the coupled port P13 is connected to the input terminal of the group delay adjuster 15.

[0017] The directional coupler 130 constituting the multiplexer 13 is composed of a transmission line 131 arranged between the input port P21 and the transmission port P22, a transmission line 132 electromagnetically coupled to the transmission line 131, and a termination resistor R4 having one end connected to the end of the transmission line 132 opposite the coupled port P23 and the other end connected to ground. In the directional coupler 130, the input port P21 is connected to the output terminal of the distributed amplifier 10, the transmission port P22 is connected to the output terminal of the BB amplifier, and the coupled port P23 is connected to the output terminal of the RF amplifier 11.

[0018] The overall configuration of the distributed amplifier 10 is the same as that of the conventional one, and will be described with reference to Fig. 25. The distributed amplifier 10 is composed of an input transmission line CPW10 having an input end connected to input terminal 1 of the distributed amplifier 10 (the output terminal of group delay adjuster 14), an output transmission line CPW20 having an end connected to output terminal 2 of the distributed amplifier 10 (the first input terminal of multiplexer 13), an input termination resistor R1 having one end connected to the end of the input transmission line CPW10 and the other end connected to ground, an output termination resistor R2 having one end connected to the input end of the output transmission line CPW20 and the other end connected to ground, and a plurality of unit cells 3 arranged along the input transmission line CPW10 and the output transmission line CPW20, and having input terminals connected to the input transmission line CPW10 and output terminals connected to the output transmission line CPW20.

[0019] The transmission line CPW10 is configured by connecting multiple transmission lines CPW1a, CPW1, and CPW1b in series. The transmission line CPW1 between the unit cells and the input-side transmission line CPW1a have different characteristic impedances. This is because, in the case of the transmission line CPW1a, the transmission line CPW1a must absorb the effects of the parasitic capacitance of circuits such as the input-side group delay adjuster 14. Similarly, the transmission lines CPW1 and CPW1b have different characteristic impedances. This is because, in the case of the transmission line CPW1b, the transmission line CPW1b must absorb the effects of the parasitic capacitance of the input termination resistor R1.

[0020] The transmission line CPW20 is configured by connecting multiple transmission lines CPW2a, CPW2, and CPW2b in series. The transmission line CPW2 between the unit cells and the input-side transmission line CPW2a have different characteristic impedances. This is because, in the case of the transmission line CPW2a, the influence of the parasitic capacitance of the output termination resistor R2 must be absorbed by the transmission line CPW2a. Similarly, the transmission lines CPW2 and CPW2b have different characteristic impedances. This is because, in the case of the transmission line CPW2b, the influence of the parasitic capacitance of circuits such as the output-side multiplexer 13 must be absorbed by the transmission line CPW2b.

[0021] 5 shows the configuration of a unit cell 3 of the distributed amplifier 10. Each unit cell 3 includes a transistor Q30 having a base terminal connected to the transmission line CPW10, a transistor Q31, a resistor R30 having one end connected to the emitter terminal of the transistor Q30 and the other end connected to the power supply voltage VEE, a resistor R31 having one end connected to the power supply voltage VEE, a resistor R32 having one end connected to the other end of the resistor R31 and the other end connected to ground, and a capacitor R33 having one end connected to the emitter terminal of the transistor Q30 and the other end connected to the power supply voltage VEE. C30, a capacitor C31 having one end connected to the connection point of resistors R31 and R32 and the other end connected to ground, a transmission line CPW30 inserted between the connection point of resistors R31 and R32 and the base terminal of transistor Q30, a transmission line CPW31 inserted between the collector terminal of transistor Q30 and the emitter terminal of transistor Q31, and a transmission line CPW32 inserted between the collector terminal of transistor Q31 and transmission line CPW20.

[0022] The loss generated in the demultiplexer 12 and the multiplexer 13 increases as the frequency increases. To compensate for this loss, the configuration shown in Figure 5 realizes a frequency peaking characteristic that increases the gain of the distributed amplifier 10 on the high-frequency side. In other words, the gain of the distributed amplifier 10 on the high-frequency side within the band is higher than the gain on the low-frequency side.

[0023] 6 shows the configuration of the RF amplifier 11. The RF amplifier 11 is composed of a series-parallel circuit 5, which is a combination of a circuit in which unit cells 4 that amplify a signal are connected in parallel and a circuit in which unit cells 4 are connected in series, and a multiplexer 6 (power combiner) that multiplexes the output signals of the paralleled unit cells 4 in the final stage.

[0024] 7 shows the configuration of the unit cell 4. The unit cell 4 includes a transistor Q40 having a base terminal connected to the input terminal 7 of the unit cell 4 and an emitter terminal connected to ground, a transistor Q41 having an emitter terminal connected to ground, transmission lines CPW40, CPW41 having one end connected to the base terminal of the transistor Q40 and the other end open, a transmission line CPW42 having one end connected to the base terminal of the transistor Q40, and a transmission line CPW43 having one end connected to the collector terminal of the transistor Q40 and the other end open. a transmission line CPW43, one end of which is connected to the collector terminal of the transistor Q40 and the other end of which is connected to the power supply voltage VC1; a transmission line CPW45, one end of which is connected to the base terminal of the transistor Q41; a transmission line CPW46, one end of which is connected to the collector terminal of the transistor Q41 and the other end of which is connected to the power supply voltage VC2; a transmission line CPW47, one end of which is connected to the other end of the transmission line CPW42 and the other end of which is connected to the base terminal of the transistor Q41; a resistor R40 having one end connected to the other end of the transmission line CPW45 and the other end connected to the power supply voltage VE2; a capacitor C40 having one end connected to the other end of the transmission line CPW42 and the other end connected to the ground; a capacitor C41 having one end connected to the other end of the transmission line CPW44 and the other end connected to the ground; a capacitor C42, a capacitor C43 having one end connected to the other end of the transmission line CPW45 and the other end connected to ground, a capacitor C44 having one end connected to the other end of the transmission line CPW46 and the other end connected to ground, a capacitor C45 having one end connected to the other end of the transmission line CPW47 and the other end connected to ground, and a capacitor C46 having one end connected to the collector terminal of the transistor Q41 and the other end connected to the output terminal 8 of the unit cell 4.

[0025] Unlike the distributed amplifier 10, the RF amplifier 11 can perform impedance matching at high frequencies using stubs (CPW40 to CPW47) or the like. This makes it easy to realize an RF amplifier 11 with gain at frequencies above fmax / 2. However, stubs are basically only effective near frequencies corresponding to a quarter wavelength. For this reason, the RF amplifier 11 tends to have a narrow bandwidth. In order to maintain flatness in the overall gain of the BB amplifier after multiplexing, it is desirable to design the RF amplifier 11 so that the gain on the low-frequency side is higher than the gain on the high-frequency side.

[0026] Furthermore, when the demultiplexer 12 and the multiplexer 13 are realized using directional couplers, the directional couplers cause losses, so the gain of the RF amplifier 11 must be higher than the gain of the distributed amplifier 10. In order to maintain flatness of the gain of the entire BB amplifier, it is desirable that the difference between the in-band gain of the RF amplifier 11 and the in-band gain of the distributed amplifier 10 be equal to the total coupling loss occurring in the demultiplexer 12 and the multiplexer 13.

[0027] Another example of the demultiplexer 12 and the multiplexer 13 is shown in Fig. 8. In the example of Fig. 8, isolated ports of the directional couplers used in the demultiplexer 12 and the multiplexer 13 are connected to the group delay adjuster 15 and the RF amplifier 11. That is, in the directional coupler 120a constituting the demultiplexer 12, the input port P11 is connected to the input terminal of the BB amplifier, the transmission port P12 is connected to the input terminal of the group delay adjuster 14, and the isolated port P14 is connected to the input terminal of the group delay adjuster 15. In the directional coupler 130a constituting the multiplexer 13, the input port P21 is connected to the output terminal of the distributed amplifier 10, the transmission port P22 is connected to the output terminal of the BB amplifier, and the isolated port P24 is connected to the output terminal of the RF amplifier 11.

[0028] By worsening the isolation characteristics of the directional couplers 120a and 130a used in the splitter 12 and the multiplexer 13, the degree of coupling between the splitter 12 and the group delay adjuster 15 and the degree of coupling between the RF amplifier 11 and the multiplexer 13 are increased.

[0029] The configuration of Figure 8 makes it possible to simplify the circuit layout at the connection between the input of the group delay adjuster 15 and the splitter 12, and at the connection between the output of the RF amplifier 11 and the multiplexer 13, thereby improving the gain and bandwidth of the entire BB amplifier.

[0030] 9, the input terminal of the group delay adjuster 15 may be connected to the isolated port P14 of the directional coupler 120a, and the output terminal of the RF amplifier 11 may be connected to the coupled port P23 of the directional coupler 130, as in the case of Fig. 4. Alternatively, as shown in Fig. 10, the input terminal of the group delay adjuster 15 may be connected to the coupled port P13 of the directional coupler 120, and the output terminal of the RF amplifier 11 may be connected to the isolated port P24 of the directional coupler 130a.

[0031] Another example of the branching filter 12 and the multiplexer 13 is shown in Fig. 11. In the example of Fig. 11, the directional coupler 120b constituting the branching filter 12 includes a transmission line 121 arranged between the input port P11 and the transmission port P12, a transmission line 122 that is electromagnetically coupled to the transmission line 121, a transmission line 123 having one end connected to one of the two ends of the transmission line 122 that is opposite to the coupled port P13, and a termination resistor R3 having one end connected to the other end of the transmission line 123 and the other end connected to ground.

[0032] The directional coupler 130b constituting the multiplexer 13 is composed of a transmission line 131 arranged between the input port P21 and the transmission port P22, a transmission line 132 that is electromagnetically coupled to the transmission line 131, a transmission line 133 having one end connected to one of the two ends of the transmission line 132 that is opposite the coupled port P23, and a termination resistor R4 having one end connected to the other end of the transmission line 133 and the other end connected to ground.

[0033] In the configuration shown in Figure 11, transmission lines 123 and 133 that are not involved in the coupling are added between the transmission lines 122 and 132 and the termination resistors R3 and R4 in the configuration shown in Figure 4. This allows the impedance of ports P12 and P13 of directional coupler 120b, which connect to group delay adjusters 14 and 15, to be adjusted, thereby reducing reflection between directional coupler 120b and group delay adjusters 14 and 15. Similarly, the impedance of ports P21 and P23 of directional coupler 130b, which connect to amplifiers 10 and 11, can be adjusted, thereby reducing reflection between directional coupler 130b and amplifiers 10 and 11. As a result, the configuration shown in Figure 11 can suppress the ripple characteristics of the entire BB amplifier and improve the band characteristics.

[0034] In the example of Fig. 11, transmission lines 123 and 133 are added to the configuration of Fig. 4, but they may also be added to the configurations of Fig. 8 to 10. Fig. 12 shows a configuration in which transmission lines 123 and 133 are added to the configuration of Fig. 8, Fig. 13 shows a configuration in which transmission lines 123 and 133 are added to the configuration of Fig. 9, and Fig. 14 shows a configuration in which transmission lines 123 and 133 are added to the configuration of Fig. 10.

[0035] The directional coupler 120c is composed of a transmission line 121 arranged between the input port P11 and the transmission port P12, a transmission line 122 that is electromagnetically coupled to the transmission line 121, a transmission line 123 having one end connected to one of the two ends of the transmission line 122 that is opposite the isolated port P14, and a termination resistor R3 having one end connected to the other end of the transmission line 123 and the other end connected to ground.

[0036] The directional coupler 130c is composed of a transmission line 131 arranged between the input port P21 and the transmission port P22, a transmission line 132 that is electromagnetically coupled to the transmission line 131, a transmission line 133 that has one end connected to the end of the transmission line 132 that is opposite the isolated port P24, and a termination resistor R4 that has one end connected to the other end of the transmission line 133 and the other end connected to ground.

[0037] The inventor proposed a BB amplifier in which the output terminal of the branching filter 12 on the distributed amplifier side is connected to the input terminal of the distributed amplifier 10, and the output terminal of the branching filter 12 on the RF amplifier side is connected to the input terminal of the RF amplifier 11 in the configuration shown in FIG. 1, i.e., a BB amplifier without group delay adjusters 14 and 15 (PCT / JP2023 / 016873).

[0038] However, in this configuration, the group delays of the distributed amplifier 10 and the RF amplifier 11 are different, which causes a problem of steps or sharp peaks in the group delay characteristics around the frequency boundary between the bands of the distributed amplifier 10 and the RF amplifier 11. In particular, in communications applications that handle wideband signals, the flatness of the group delay characteristics has a significant impact on signal quality, so it is desirable to improve the flatness of the group delay characteristics. Therefore, in this embodiment, group delay adjusters 14 and 15 are added.

[0039] 15 shows the simulation results of the transmission characteristics (S21) of a BB amplifier without group delay adjusters 14, 15, and FIG. 16 shows the simulation results of the group delay characteristics of a BB amplifier without group delay adjusters 14, 15. The frequency that marks the boundary between the bands of the distributed amplifier 10 and the RF amplifier 11 is around 220 GHz. It can be seen that a peak Dp occurs in the group delay characteristics around 220 GHz. It can also be seen that a step Dd occurs in the group delay characteristics before and after 220 GHz. It can be seen that a large dip occurs in the transmission characteristics.

[0040] 17 shows the simulation results of the output waveform of the BB amplifier when a 500 Gbps PAM4 (4-Level Pulse Amplitude Modulation) signal is input to the BB amplifier without the group delay adjusters 14 and 15. As can be seen from FIG. 17, the eye opening is closed.

[0041] FIG. 18 shows the results of a simulation of the transmission characteristic (S21) of the BB amplifier of this embodiment shown in FIG. 1 , and FIG. 19 shows the results of a simulation of the group delay characteristic of the BB amplifier of this embodiment. Here, the simulation shows a case where a group delay equivalent to the group delay difference (step Dd in FIG. 16 ) between the distributed amplifier 10 and the RF amplifier 11 is added by the group delay adjuster 14. That is, the difference obtained by subtracting the group delay of the group delay adjuster 15 from the group delay of the RF amplifier 11 is approximately equal to the difference obtained by subtracting the group delay of the distributed amplifier 10 from the group delay of the RF amplifier 11. FIG. 19 shows that the steps and peaks in the group delay characteristic of the BB amplifier without the group delay adjusters 14 and 15 are improved. Furthermore, FIG. 18 shows that the dip in the transmission characteristic of the BB amplifier without the group delay adjusters 14 and 15 is also improved.

[0042] 20 shows the simulation results of the output waveform of the BB amplifier when a 500 Gbps PAM4 signal is input to the BB amplifier of this embodiment. As can be seen from FIG. 20, the eye opening is improved compared to a BB amplifier without the group delay adjusters 14 and 15.

[0043] Second Example Generally, the group delay of the RF amplifier 11 tends to be larger than that of the distributed amplifier 10. In the RF amplifier 11, the gain obtained from a single transistor is smaller than that of the distributed amplifier 10. Therefore, in order to obtain a gain equal to or greater than that of the distributed amplifier 10, it is necessary to increase the number of cascade-connected transistor stages. As a result, the group delay of the RF amplifier 11 increases.

[0044] 21, the group delay adjuster 14 is arranged only on the distributed amplifier 10 side. The group delay added by the group delay adjuster 14 is approximately equal to the difference between the group delay of the RF amplifier 11 and the group delay of the distributed amplifier 10. This makes it possible to improve the gain on the RF amplifier 11 side, and also improve the high-frequency gain of the BB amplifier.

[0045] [Third Embodiment] The configuration of the group delay adjuster 14 described in the first and second embodiments is shown in Figure 23. The group delay adjuster 14 is composed of a plurality of transmission lines 142 connected in series between an input terminal 140 and an output terminal 141, and a plurality of variable capacitors C140, one end of which is connected to the connection point of the two transmission lines 142 and the other end of which is connected to ground. The amount of group delay can be adjusted by changing the capacitance value of the variable capacitor C140. The configuration of the group delay adjuster 15 is similar to that of the group delay adjuster 14. In this way, in the first and second embodiments, a positive group delay is added by the group delay adjusters 14 and 15.

[0046] On the other hand, in this embodiment, as shown in Figure 22, the group delay adjuster 15a is arranged only on the RF amplifier 11 side. The group delay adjuster 15a needs to have a circuit with a negative group delay characteristic. The configuration of the group delay adjuster 15a is shown in Figure 24. The group delay adjuster 15a is composed of an inductor L150 having one end connected to an input terminal 150 of the group delay adjuster 15a, a resistor R150 having one end connected to the other end of the inductor L150 and the other end connected to an output terminal 151 of the group delay adjuster 15a, and a capacitor C150 having one end connected to the input terminal 150 and the other end connected to the output terminal 151.

[0047] The group delay added by the group delay adjuster 15a is approximately equal to the negative value of the difference between the group delay of the RF amplifier 11 and the group delay of the distributed amplifier 10. Within a limited bandwidth, it is possible to achieve a negative group delay using the RLC resonant circuit structure shown in Fig. 24. When the group delay of the RF amplifier 11 is larger than the group delay of the distributed amplifier 10, it is possible to reduce the group delay of the entire BB amplifier and reduce signal delay by arranging the negative group delay adjuster 15a on the RF amplifier 11 side, as in this embodiment.

[0048] Some or all of the above embodiments can be described as, but are not limited to, the following supplementary notes.

[0049] (Supplementary Note 1) A baseband amplifier of the present invention comprises a distributed amplifier, an RF amplifier configured to have higher frequency pass characteristics than the distributed amplifier, a branching filter configured to output, from a first output terminal, a signal of an input signal that includes at least a signal component that is equal to or lower than a high-frequency cutoff frequency of the distributed amplifier, and to output, from a second output terminal, a signal of the input signal that includes at least a signal component that is equal to or higher than a low-frequency cutoff frequency of the RF amplifier, to the RF amplifier, a first group delay adjuster inserted between the first output terminal of the branching filter and an input terminal of the distributed amplifier, and a multiplexer configured to multiplex the signal amplified by the distributed amplifier and the signal amplified by the RF amplifier.

[0050] (Supplementary Note 2) The baseband amplifier according to Supplementary Note 1 further comprises a second group delay adjuster inserted between a second output terminal of the demultiplexer and an input terminal of the RF amplifier.

[0051] (Supplementary Note 3) In the baseband amplifier according to Supplementary Note 2, the difference obtained by subtracting the group delay of the second group delay adjuster from the group delay of the first group delay adjuster is approximately equal to the difference obtained by subtracting the group delay of the RF amplifier from the group delay of the distributed amplifier.

[0052] (Supplementary Note 4) A baseband amplifier of the present invention comprises a distributed amplifier, an RF amplifier configured to have higher frequency pass characteristics than the distributed amplifier, a branching filter configured to output a signal of an input signal including at least a signal component not exceeding a high-frequency cutoff frequency of the distributed amplifier from a first output terminal to the distributed amplifier, and to output a signal of the input signal including at least a signal component not less than a low-frequency cutoff frequency of the RF amplifier to a second output terminal, a group delay adjuster inserted between the second output terminal of the branching filter and an input terminal of the RF amplifier, and a multiplexer configured to multiplex the signal amplified by the distributed amplifier and the signal amplified by the RF amplifier.

[0053] 3, 4... Unit cell, 5... Series-parallel circuit, 6, 13... Multiplexer, 14, 15, 15a... Group delay adjuster, 10... Distributed amplifier, 11... RF amplifier, 12... Branching filter, 120, 120a to 120c, 130, 130a to 130c... Directional couplers, 121 to 123, 131 to 133, 142, CPW1, CPW1a, CPW1b, CPW2, CPW2a , CPW2b, CPW10, CPW20, CPW30 to CPW32, CPW40 to CPW47...transmission lines, Q30, Q31, Q40, Q41...transistors, R1 to R4, R30 to R32, R40, R41, R150...resistors, C30, C31, C40 to C46, ​​C150...capacitors, C140...variable capacitor, L150...inductor.

Claims

1. A baseband amplifier comprising: a distributed amplifier; an RF amplifier configured to have higher frequency pass characteristics than said distributed amplifier; a branching filter configured to output, from a first output terminal, a signal of an input signal that includes at least a signal component below the high-frequency cutoff frequency of said distributed amplifier, and to output, from a second output terminal, a signal of said input signal that includes at least a signal component above the low-frequency cutoff frequency of said RF amplifier, to said RF amplifier; a first group delay adjuster inserted between the first output terminal of said branching filter and the input terminal of said distributed amplifier; and a multiplexer configured to multiplex the signal amplified by said distributed amplifier and the signal amplified by said RF amplifier.

2. A baseband amplifier according to claim 1, further comprising a second group delay adjuster inserted between the second output terminal of said branching filter and the input terminal of said RF amplifier.

3. A baseband amplifier according to claim 2, wherein the difference between the group delay of said first group delay adjuster and the group delay of said second group delay adjuster is approximately equal to the difference between the group delay of said RF amplifier and the group delay of said distributed amplifier.

4. A baseband amplifier comprising: a distributed amplifier; an RF amplifier configured to have higher frequency pass characteristics than said distributed amplifier; a branching filter configured to output from a first output terminal to said distributed amplifier a signal of an input signal that includes at least a signal component below the high-frequency cutoff frequency of said distributed amplifier, and to output to a second output terminal a signal of said input signal that includes at least a signal component above the low-frequency cutoff frequency of said RF amplifier; a group delay adjuster inserted between the second output terminal of said branching filter and the input terminal of said RF amplifier; and a multiplexer configured to multiplex the signal amplified by said distributed amplifier and the signal amplified by said RF amplifier.

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