Electro-Optical Mixer
Patent Information
- Application Number
- JP2024545908
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-02-01
- Filing Date
- 2023-02-01
- Publication Date
- 2025-04-22
- Estimated Expiration
- 2043-02-01
Smart Images
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Abstract
Description
[Technical field]
[0001] The present invention relates to an electro-optical mixer. [Background technology]
[0002] In many use cases, optical data is transmitted over long distances using optical fibers. Optical fibers are also used in radar applications to distribute local oscillator signals (LO). To transmit data or radar signals over the air, the optical signal must be converted to an electrical signal before being upconverted.
[0003] Conversion of the optical signal to an electrical signal is performed using a transimpedance amplifier (TIA). Upconversion to the desired RF band is then performed using an electrical mixer. The output signal from the TIA can then be further preprocessed using a DC-balanced buffer and a variable gain amplifier (VGA), after which this signal is multiplied by another signal using a mixer.
[0004] A block diagram showing the most relevant prior art is shown in Figure 1. In this case, the optical signal is routed over a fiber from a switching center CO to an optical baseband receiver BPR, where it is pre-processed (by a processing method using, as an example, photodiodes, transimpedance amplifiers, DC-balanced buffers, and variable gain amplifiers (VGAs)) and then up-converted to the desired RF band in an electrical stage TX using a mixer (and further signals). In this case, the optical baseband receiver BPR and the electrical stage TX are provided, for example, in a BICMOS integrated circuit.
[0005] In this process, both the transimpedance amplifier and the electrical mixer increase the overall system complexity. Furthermore, the transimpedance amplifier is approximately 0.25 mm 2 , which increases the cost of such a system.
[0006] Furthermore, each individual component has a certain bandwidth. By interconnecting two components, the bandwidth of the entire system is determined by the bandwidth of the individual components and thus by the component with the lowest bandwidth. To detect high-frequency optical signals, a separate TIA must be used to minimize the effects of parasitic capacitance. This TIA generates additional noise.
[0007] These components also generate power losses, impairing the efficiency of the system. Therefore, this solution is not suitable for use in low-power applications or battery-operated systems. It should also be noted that providing a transimpedance amplifier as a separate component increases the risk of failure of the entire system. In some applications, it may be necessary to use only a specific frequency band from an optical signal of any desired width. This is usually achieved using a filter behind the TIA. This channel selection filter is based on passive components.
[0008] Considering that real passive components always have parasitic resistances, the noise increases enormously. Moreover, (passive) components require a large chip area, thereby significantly increasing the system cost. In some applications, it may be necessary to turn off a single unit while the data signal and / or clock signal are still transmitted to other systems via the fiber. Various techniques can be used to implement this. The optical power at the photodiode can be individually set to 0 by a Mach-Zehnder Modulator (MZM) in front of the photodiode. Such an approach is shown in Figure 2. Here, the optical input signal from the laser diode LD is directed to the Mach-Zehnder Modulator MZM. The output signal from the Mach-Zehnder Modulator MZM is also optical and still has to be converted to an electrical signal using a photodiode PD. This electrical signal is a current signal. For further processing, this current signal still has to be converted to a voltage signal in a transimpedance amplifier.
[0009] Given that Mach-Zehnder modulators require a very large area and very high control voltages, this solution is disadvantageous, especially for integrated circuits and highly scaled technologies. To control a Mach-Zehnder modulator, voltages in the range of 2-3 V are therefore required. For modern transistors with dimensions in the nanometer range, this voltage range can already lead to failure of driver components. Moreover, these driver components increase the mixer noise.
[0010] Furthermore, the MZM requires several square millimeters of chip area, which increases the price of the entire system.Finally, the MZM only has a bandwidth in the range below 30 GHz, making this solution unsuitable for HF applications.As an alternative to the Mach-Zehnder modulator, the supply voltage can be switched off.
[0011] However, the drawback of this technique is that strong currents must flow through the corresponding switching transistors. Cooling capacity must be planned to compensate for the corresponding power dissipation in the transistors, which significantly increases the complexity of the system. Yet another alternative is to use an analog latch to freeze the signal in a DC state after the transimpedance amplifier.
[0012] However, analog latches are very expensive in the mm-wave range and significantly increase the system costs. Moreover, in known systems, insofar as they are available, matching networks are designed only as bandpass, so that in principle it is not possible to select different frequency bands. Based on this, the object of the present invention is to identify a solution that avoids one or more of the problems in the prior art. [Brief description of the drawings]
[0013] This object is achieved by an electro-optical mixer having an electrical output as claimed in claim 1. Further advantageous embodiments of the invention are the subject of the dependent claims, the description and the drawings. Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Figure 1] 1 is a prior art embodiment. [Diagram 2] 1 is a further embodiment according to the prior art. [Diagram 3] FIG. 1 is a schematic diagram of an embodiment of the present invention. [Figure 4] FIG. 4 is a further schematic diagram of a further embodiment of the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] The present invention will be explained in more detail below with reference to the drawings. In this connection, it is noted that various aspects are described which can be used individually or in combination. In other words, any aspect can be used in the various embodiments of the invention, unless expressly stated as purely alternative.
[0015] Furthermore, for the sake of brevity, in the following, reference will generally be made to only one entity. However, unless expressly stated otherwise, the present invention may also include a plurality of related entities. In this context, the use of the words "a", "an" and "one" should only be understood as indicating that at least one entity is used in a single embodiment.
[0016] To the extent that methods are described below, the individual method steps can be arranged and / or combined in any desired order unless the context clearly indicates otherwise. Further, unless otherwise specified, the methods can be combined with each other.
[0017] As a rule, specifications with numerical values should not be understood as exact values, but as including a tolerance of + / - 1% to + / - 10%. References to standards, specifications or norms should be understood as references to the standards, specifications or norms in force at the time of filing the application and / or at the time of filing the priority application, if priority is claimed. However, this should not be understood as a general exclusion of applicability to subsequent or replacing standards, specifications or norms.
[0018] 3 and 4 show an electro-optical mixer 1 with an electrical output according to an embodiment of the present invention. The electro-optical mixer 1 comprises at least one photodiode PD for converting an incoming optical signal. The electro-optical mixer 1 further comprises at least one first terminal and at least one second terminal, whereby a first voltage source V1 can be connected to the or each first terminal (in each case) and a second voltage source V2 can be connected to the or each second terminal (in each case).
[0019] Alternatively, the first power supply I1 can be connected to the or each first terminal (in each case) and the second power supply I2 can be connected to the or each second terminal (in each case).
[0020] The electro-optical mixer 1 also comprises at least one terminal for a small-signal ground potential for the first voltage source V1 and for the second voltage source V2. The small-signal ground potential can be any desired potential, but in particular the ground potential of the entire circuit.
[0021] The electro-optical mixer 1 comprises a first partial matching network represented by Z2 and Z4 arranged on the anode side of the photodiode PD, whereby a part of the first partial matching network (in this case Z2) can be switchably connected to a terminal for a second voltage source V2 using a switch S2, whereby another part of the first partial matching network (in this case Z4) can be switchably connected to a terminal for a small signal ground potential using a switch S2.
[0022] The electro-optical mixer 1 comprises a second partial matching network represented by Z1 and Z3 arranged on the cathode side of the photodiode PD, whereby a part of the second partial matching network (in this case Z1) can be switchably connected to a terminal for a first voltage source V1 using a switch S1, whereby another part of the second partial matching network (in this case Z3) can be switchably connected to a terminal for a small signal ground potential using a switch S1'.
[0023] In this case, the matching network must have impedance matching, which means that an AC voltage separation by a single capacitor (as a decoupling element) should not be understood as a matching network. The elements of the first partial matching network (in this case Z2, Z4) and the second partial matching network (in this case Z1, Z3) are characterized by inductive and / or resistive and / or capacitive properties.
[0024] The electro-optical mixer 1 further comprises a first decoupling element C1 arranged on the cathode side of the photodiode PD and a second decoupling element C2 arranged on the anode side of the photodiode PD, the first decoupling element C1 and the second decoupling element C2 being characterized by inductive and / or resistive and / or capacitive properties.
[0025] In operation, an electrical output signal can be provided between the sides of the first decoupling element C1 and the second decoupling element C2 facing away from the photodiode PD. The presented arrangement can be used to provide a simple, space-saving and frequency tunable solution, which can also be turned off.
[0026] In one embodiment of the invention, the electrical output signals are fed to transimpedance amplifiers TIA1, TIA2, respectively. In a further embodiment of the invention, the switches S1, S2, S1', S2' are designed as any desired switching elements, but in particular as semiconductor switches, e.g. as transistors.
[0027] According to one embodiment of the invention, the circuit can operate as an optical receiver, given an appropriate switch selection. According to yet another embodiment of the invention, the electro-optical mixer can be deactivated using the switches S1, S2, S1', S2'. Without limiting the generality of the invention, the switch positions of the switches S1, S2, S1', S2' can be controlled by any desired signal, in particular by an optical signal and / or by an electrical signal and / or by a mechanical signal.
[0028] In one embodiment of the present invention, the elements of the first partial matching network (in this case Z2, Z4) and the second partial matching network (in this case Z1, Z3) are characterized by inductive properties, whereby the inductive properties are provided by coils and / or lines.
[0029] In one embodiment of the present invention, the elements of the first partial matching network (in this case Z2, Z4) and the second partial matching network (in this case Z1, Z3) are alternatively or additionally characterized by capacitive characteristics, whereby the capacitive characteristics are provided by capacitors and / or lines.
[0030] Without limiting the generality of the invention, the system is implemented in semiconductor technology, for example BiCMOS. However, the system can also be implemented using discrete components. However, it is clear that the electro-optical mixer can also be partially integrated and include individual elements, for example as discrete components.
[0031] In all embodiments, the system can be adapted to be able to operate with any desired polarization. The system can in particular operate with purely TE polarization or purely TM polarization. The system can also operate with purely TE and purely TM polarization, thus providing for example processing for polarization multiplexing.
[0032] In the embodiment shown as an example in Fig. 3, an optical signal RF is detected in a photodiode PD and converted into an electrical signal, and a first partial matching network and a second partial matching network combine the electrical signal to generate or select a frequency band through impedance matching provided by the first partial matching network and the second partial matching network.
[0033] In the example shown in FIG. 3, the impedances Z1...Z4 are formed by inductors (but are not limited to this), but the implementation of the impedances Z1...Z4 is not limited to coils and capacitors and other passive components can also be used.
[0034] As a result of the anode and cathode impedance of the photodiode PD depending on the operating point, a channel / frequency band can be selected by changing the voltages V1, V2 or the currents I1, I2, because for each different voltage, the matching network formed from the first partial matching network and the second partial matching network interacting with the impedance of the photodiode PD resonates with (other frequencies).
[0035] The actual mixing process is provided by an H-bridge consisting of S1, S2, S1', S2', Z1, Z2, Z3, Z4, and PD.
[0036] If the voltage sources V1 and V2 each provide a voltage different from 0 that is larger in magnitude (compared to the small signal ground potential), the following can be observed: When the switches S1 and S1' are closed and the remaining switches are open, the photodiode PD is in the blocking direction and a dark current is detected in addition to the photocurrent. However, when the switches S2 and S2' are closed and the remaining switches are open, the diode is in forward operation and the current is dominated by the diode current, so that the photocurrent is no longer detectable.
[0037] However, if switches S1' and S2' are closed and the other switches are open, the bandwidth of the photodiode PD is reduced so that only low frequency signals can be detected. However, if switches S2 and S2' are closed (long-term) and the remaining switches are open, I photo < diode In this case, mixer 1 is turned off.
[0038] Obviously, these explanations also apply correspondingly to positive currents I1, I2, each different from 0. Of course, it should be noted that the explanations specified above are also valid if the voltage sources V1 and V2, each provide a voltage different from 0 that is smaller (compared to the small signal mass potential), whereby the indices should be swapped. Obviously, these explanations also apply correspondingly to negative currents I1, I2, each different from 0.
[0039] Figure 4 shows a further embodiment of the invention, in which the passive cores remain as in figure 3. However, if the capacitances are very large, i.e. C1, C2 →∞, and the impedances Z1, Z2, Z3, Z4 (e.g. inductances) are appropriately selected, wideband signals can also be detected.
[0040] In this case, the current can be converted to a voltage using transimpedance amplifiers TIA1 and TIA2. However, if power is desired at the output, the voltage can be converted to power at a specific impedance by an optional matching network (at the output of transimpedance amplifiers TIA1 and TIA2).
[0041] In addition, the system is not limited to only two transimpedance amplifiers TIA. Any desired number of TIAS sensitive to different frequencies can be used. After selecting the appropriate transimpedance amplifier, channel selection can be performed. The embodiment shown in FIG. 4 allows for both wideband and narrowband operation.
[0042] The embodiments presented herein utilize H-bridges as opposed to Gilbert cells or nonlinearized components. Additionally, the system can be implemented as a broadband system or using channel selection. The system also provides the option of being deactivatable.
[0043] The electro-optical mixer according to the invention comprises an H-bridge that allows the optical signal to be directly multiplied with an electrical signal without the presence of a transimpedance amplifier. The electro-optical mixer according to the invention consumes less power, is less complex and has less noise. Depending on the size of the TIA and / or Mach-Zehnder modulator, the chip area is also smaller. The bandwidth can be adjusted by using an appropriate partial matching network. Likewise, the bandwidth can be influenced by the semiconductor technology used. If transistors are used as switches S1, S2, S1', S2', the voltage (compared to Mach-Zehnder modulators) should be sufficient to reach only voltages >3UT (≈75mV), which is significantly less than 2-3V.
Claims
1. An electro-optical mixer (1) having an electrical output, A photodiode (PD) that converts an incident optical signal; a first terminal; - a second terminal; a first voltage source (V1) can be connected to the first terminal and a second voltage source (V2) can be connected to the second terminal, or a first power supply (I1) can be connected to the first terminal and a second power supply (I2) can be connected to the second terminal; a terminal for a small signal ground potential for the first voltage source (V1) and for the second voltage source (V2); a first partial matching network (Z2, Z4) arranged on the anode side of the photodiode (PD), a part of the first partial matching network (Z2) being switchably connectable (S2) to the terminal for the second voltage source (V2), and another part of the first partial matching network (Z4) being switchably connectable (S2') to the terminal for the small signal ground potential; a second partial matching network (Z1, Z3) arranged on the cathode side of the photodiode (PD), a part of the second partial matching network (Z1) being switchably connectable (S1) to the terminal for the first voltage source (V1) and another part of the second partial matching network (Z3) being switchably connectable (S1') to the terminal for the small signal ground potential; the elements of the first partial matching network (Z2, Z4) and the second partial matching network (Z1, Z3) are characterized by inductive and / or resistive and / or capacitive properties, a first capacitive element (C1) arranged on the cathode side of the photodiode (PD); a second capacitive element (C2) arranged on the anode side of the photodiode (PD); the first decoupling element (C1) and the second decoupling element (C2) are characterized by inductive and / or resistive and / or capacitive properties, An electro-optical mixer (1) capable of providing, in operation, an electrical output signal between the sides of the first decoupling element (C1) and the second decoupling element (C2) facing away from the photodiode (PD).
2. 2. An electro-optical mixer as claimed in claim 1, characterized in that said electrical output signals are respectively fed to transimpedance amplifiers (TIA1, TIA2).
3. 3. An electro-optical mixer according to claim 1 or 2, characterized in that the switches (S1, S2, S1', S2') are designed as any desired switching elements.
4. 3. An electro-optical mixer according to claim 2, characterized in that the switches (S1, S2, S1', S2') are designed as semiconductor switches.
5. 2. An electro-optical mixer as claimed in claim 1, characterised in that, given appropriate switch selections, said circuit can operate as an optical receiver.
6. Electro-optical mixer according to claim 2, characterized in that the electro-optical mixer can be turned off by the switches (S1, S2, S1', S2').
7. Electro-optical mixer according to claim 2, characterized in that the switch positions of the switches (S1, S2, S1', S2') can be controlled by any desired signal.
8. Electro-optical mixer according to claim 1, characterized in that the switch positions of the switches (S1, S2, S1', S2') can be controlled by optical and / or electrical and / or mechanical signals.
9. 2. The electro-optical mixer of claim 1, wherein the elements of the first partial matching network (Z2, Z4) and the second partial matching network (Z1, Z3) are characterized by inductive properties, the inductive properties being provided by coils and / or lines.
10. 2. The electro-optical mixer of claim 1, wherein the elements of the first partial matching network (Z2, Z4) and the second partial matching network (Z1, Z3) are characterized by capacitive properties, the capacitive properties being provided by capacitors and / or lines.
11. Electro-optical mixer according to claim 1, characterized in that the system is implemented in semiconductor technology.
12. 10. The electro-optical mixer of claim 1, wherein the system is implemented using discrete components.
13. 2. An electro-optical mixer as claimed in claim 1, characterized in that the system can operate with any desired polarization.
14. Electro-optical mixer according to claim 1, characterized in that the system is capable of operating purely with TE polarized light and / or purely with TM polarized light.