EP4457561A1 - Electro-optical mixer - Google Patents

Abstract

The invention relates to an electro-optical mixer (1) having an electrical output, the electro-optical mixer comprising: - a photodiode (PD) for converting an incident optical signal, - a first and a second terminal, to which first terminal a first voltage supply (V1) and to which second terminal a second voltage supply (V2) can be connected or to which first terminal a first current supply (I1) and to which second terminal a second current supply (I2) can be connected, - a terminal for a small-signal ground potential for the first voltage supply (V1) and the second voltage supply (V2), - a first partial adaptation network (Z2, Z4) located on the anode side of the photodiode (PD), one part of which first partial adaptation network (Z2) can be switchably (S2) connected to the terminal for the second voltage supply (V2) and another part of which first partial adaptation network (Z4) can be switchably (S2') connected to the terminal for the small-signal ground potential, - a second partial adaptation network (Z1, Z3) located on the cathode side of the photodiode (PD), one part of which second partial adaptation network (Z1) can be switchably (S1) connected to the terminal for the first voltage supply (V1) and another part of which second partial adaptation network (Z3) can be switchably (S1') connected to the terminal for the small-signal ground potential, the elements of the first partial adaptation network (Z2, Z4) and of the second partial adaptation network (Z1, Z3) having an inductive and/or resistive character and/or capacitive character, - a first decoupling element (C1), which is located on the cathode side of the photodiode (PD), - a second decoupling element (C2), which is located on the anode side of the photodiode (PD), the first decoupling element (C1) and the second decoupling element (C2) having an inductive and/or resistive character and/or capacitive character, wherein during operation an electrical output signal can be provided between the sides of the first decoupling element (C1) and of the second decoupling element (C2) which are remote from the photodiode (PD).

Description

Electro-optical mixer

The invention relates to an electro-optical mixer.

background

In many applications, optical data is sent over long distances using glass fibers. Glass fibers are also used in the radar area to distribute the local oscillator signal (LO).

In order to send the data or the radar signal wirelessly, the optical signal has to be converted into an electrical signal before it is upconverted.

Optical signals are converted into electrical signals using transimpedance amplifiers (TIA). Up-conversion to the desired RF band is then performed using an electrical mixer.

The output signal of the TIA can then be pre-processed using a DC-balanced buffer and a variable gain amplifier (VGA) before this signal is multiplied by another signal using a mixer.

A block diagram representing the closest prior art is shown in FIG. There, an optical signal is routed from a switching center CO via a fiber to an optical baseband receiver BPR and pre-processed there (via exemplary processing using a photodiode, transimpedance amplifier, DC-balanced buffer and a variable gain amplifier (VGA)) and then in an electrical Stage TX mixed up to the desired RF band by means of a mixer (and another signal). The optical baseband receiver BPR and the electrical stage TX are made available, for example, on a BICMOS integrated circuit. In this case, both the transimpedance amplifier and the electrical mixer increase the complexity of the overall system.

In addition, the transimpedance amplifier requires a separate chip area of the order of approx. 0.25 mm ² , which increases the costs of such a system.

In addition, each individual component has a certain bandwidth. By interconnecting the two components, the bandwidth of the overall system is determined by the bandwidth of the individual components and thereby by the component with the lowest bandwidth. To detect high frequency optical signals, a separate TIA must be used to minimize the influence of parasitic capacitance. This TIA creates additional noise.

Furthermore, the components generate power loss, which impairs the efficiency of the system. Therefore, this solution is not suitable for use in low-power applications or battery-powered systems.

It is also 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 certain frequency band from the optical signal of any width. This is usually implemented with a filter behind the TIA. This Channel Select Filter is based on passive components.

Since real passive components always have a parasitic resistance, the noise increases enormously.

Furthermore, the (passive) components require a great deal of chip area, which means that the costs for the system rise sharply. In some applications it may be necessary for a single unit to be switched off while a data and/or clock signal continues to be forwarded on the fiber to other systems.

Various techniques can be used to implement this.

By using a Mach-Zehnder Modulator (MZMs) in front of a photodiode, the optical power at the photodiode can be set to zero individually. Such an approach is shown in FIG.

There, an optical input signal from a laser diode LD is routed to a Mach-Zehnder modulator MZM. The output signal of the Mach-Zehnder modulator MZM is again optical and must first be converted into an electrical signal by means of a photodiode PD. This electrical signal is then a current signal. For further processing, this current signal must be converted into a voltage signal in a transimpedance amplifier.

Since Mach-Zehnder modulators require a large area and very high control voltages, this solution is disadvantageous for integrated circuits and, in particular, extremely scaled technologies.

For example, voltages in the range of 2-3V are required to control a Mach-Zehnder modulator. For modern transistors with dimensions in the nanometer range, this voltage range can already lead to failure of the driver components.

Furthermore, these driver components in turn increase the noise of the mixer.

Furthermore, the MZM requires several square millimeters of chip area, which in turn increases the overall price of the system.

Ultimately, MZM only have a bandwidth in the <30 GHz range, which makes this solution unsuitable for HF applications. As an alternative to Mach-Zehnder modulators, the supply voltage can be switched off.

However, this technique has the disadvantage that high currents would have to flow through the corresponding switching transistors. In order to compensate for the corresponding power loss in the transistors, cooling capacities would have to be planned, which would increase the complexity of the system enormously.

Another alternative would be to use an analog latch to freeze the signals in a DC state after the transimpedance amplifier.

However, analog latches are very expensive in the mm-wave range, which would greatly increase the cost of the system.

Furthermore, in the known systems—where available—the matching network is only designed as a bandpass filter, so that it is generally not possible to select different frequency bands.

Proceeding from this, it is the object of the invention to specify a solution which avoids one or more problems from the prior art.

The object is achieved by an electro-optical mixer with an electrical output according to claim 1. Further advantageous refinements of the invention are the subject matter of the dependent claims, the description and the figures.

Embodiments of the present invention are described by way of example with reference to the attached drawings, in which:

1 shows an embodiment according to the prior art,

2 shows a further embodiment according to the prior art, 3 shows a schematic representation of embodiments of the invention,

4 shows a further schematic representation of further embodiments of the invention.

Detailed presentation of the invention with reference to the drawings

In the following the invention will be illustrated in more detail with reference to the figures. It should be noted that different aspects are described, which can be used individually or in combination. That is, each aspect can be used with different embodiments of the invention unless explicitly presented as purely alternative.

Furthermore, for the sake of simplicity, only one entity will generally be referred to below. Unless explicitly noted, however, the invention can also have several of the entities concerned. In this respect, the use of the words “a”, “an” and “an” is only to be understood as an indication that at least one entity is used in a simple embodiment.

Insofar as methods are described below, the individual steps of a method can be arranged and/or combined in any order, unless something different is explicitly stated in the context. Furthermore, the processes can be combined with one another, unless expressly stated otherwise.

Specifications with numerical values are generally not to be understood as exact values, but also include a tolerance of +/- 1% to +/- 10%.

References to standards or specifications or norms are to be understood as references to standards or specifications or norms which are/were applicable at the time of filing and/or - insofar as priority is claimed - also at the time of priority filing. However, this is not to be understood as a general exclusion of applicability to subsequent or superseding standards or specifications or norms. Referring to Figures 3 and 4, there is shown an electrical output electro-optical mixer 1 in accordance with embodiments of the invention.

The electro-optical mixer 1 has at least one photodiode PD for converting an incident optical signal.

Furthermore, the electro-optical mixer 1 has at least one first connection and at least one second connection, a first voltage supply Vi being connected to the first connection/the respective first connections (each) and a first voltage supply Vi to the second connection/the/the respective second connections (each). second power supply V ₂ can be connected.

As an alternative to this, a first power supply 11 can be connected to the first connection/the respective first connections (each) and a second power supply ₁₂ can be connected to the second connection/the/the respective second connections (each).

The electro-optical mixer 1 also has at least one connection for a small-signal ground potential for the first voltage supply Vi and the second voltage supply V ₂ . The small-signal ground potential can be any potential, but in particular also the ground potential of the entire circuit.

The electro-optical mixer 1 has a first partial matching network - represented by Z ₂ , Z ₄ - which is arranged on the anode side of the photodiode PD, with part of the first partial matching network - here Z ₂ - being switchable with the connection for the second voltage supply V ₂ can be connected by means of switch S ₂ , and wherein another part of the first partial matching network - here Z4 - can be connected to the connection for the small-signal ground potential in a switchable manner by means of switch S ₂ '.

The electro-optical mixer 1 has a second partial matching network - represented by Zi, Z3 - which is arranged on the cathode side of the photodiode PD, with a part of the second Sub-matching network - here Zi - can be connected to the connection for the first voltage supply Vi in a switchable manner by means of a switch Si, and another part of the second sub-matching network - here Z3 - can be connected to the connection for the small-signal ground potential by means of a switch Si'.

Matching networks are to be seen as impedance matching, i.e. an AC voltage separation through a sole capacitor (as a decoupling element) is not to be understood as a matching network.

The elements of the first partial matching network—here Z ₂ , Z4—and the second partial matching network—here Zi, Z ₃ —have an inductive and/or resistive character and/or a capacitive character.

The electro-optical mixer 1 further comprises a first decoupling element Ci, which is arranged on the cathode side of the photodiode PD, and a second decoupling element C ₂ , which is arranged on the anode side of the photodiode PD.

The first decoupling element Ci and the second decoupling element C ₂ in turn have an inductive and/or resistive character and/or a capacitive character.

During operation, an electrical output signal can then be provided between the sides of the first decoupling element Ci and of the second decoupling element C ₂ that are remote from the photodiode PD.

With the arrangement presented, a simple, space-saving, frequency-adjustable solution can be provided, which can also be switched off.

In one embodiment of the invention, the electrical output signal is one at a time

Transimpedance amplifier TlAi, TIA ₂ supplied. In a further embodiment of the invention, the switches Si, S2, Si′, S2′ are designed as any switching element, but in particular as semiconductor switches, for example as transistors.

According to one embodiment of the invention, with a suitable switch selection, the circuit can operate as an optical receiver.

According to another embodiment of the invention, the electro-optical mixer can be deactivated by means of the switches Si, S2, Si′, S2′.

Without restricting the generality of the invention, the switching positions of the switches Si, S2, Si', S2' can be controlled by any signal, in particular by an optical signal and/or by an electrical signal and/or by a mechanical signal.

In one embodiment of the invention, the elements of the first partial matching network—here Z2, _Z4 —and the second partial matching network—here Zi, Z3—have an inductive character, with the inductive character being provided by coils and/or by lines.

In one embodiment of the invention, the elements of the first partial matching network—here Z2, _Z4 —and the second partial matching network—here Zi, Z3—have an alternative or additional capacitive character, with the capacitive character being provided by capacitors and/or lines.

Without restricting the generality of the invention, the system is implemented in semiconductor technology, e.g.

BiCMOS, implemented.

However, the system can also be implemented with discrete components. However, the electro-optical mixer can obviously also be partially integrated and, for example, have individual elements as discrete components.

In all of the embodiments, it can be provided that the system can work with any polarized light. In particular, the system can work with purely TE-polarized light or with purely TM-polarized light. The system can also work with purely TE-polarized light and with purely TM-polarized light and thus provide processing for polarization multiplexing, for example.

In the exemplary embodiment of FIG. 3, the optical signal RF is detected in the photodiode PD and converted into an electrical signal. The first sub-matching network and the second sub-matching network decouple the electrical signal and generate or select the frequency band through the impedance matching, which is provided by the first sub-matching network and the second sub-matching network.

In the example in FIG. 3, the impedances Zi .

Because the anode and cathode impedance of the photodiode PD depend on the operating point, the channel/frequency band can be selected by varying the voltages Vi, V ₂ or currents , h, since the matching network is formed from the first partial matching network and becomes resonant for (other frequencies) in the second partial matching network in interaction with the impedances of the photodiode PD.

The actual mixing process is provided in the H-bridge consisting of Si, S ₂ , Si', S ₂ ', Zi, Z ₂ , Z ₃ , Z4 and PD.

In the event that the voltage supplies Vi and V ₂ each provide a non-zero voltage (compared to the small-signal ground potential) that is larger in magnitude, the following can now be observed: If the switches Si and Si' are closed and the other switches are open, the photodiode PD is in the reverse direction and the dark current plus the photocurrent is detected.

If, on the other hand, the switches S2 and S2' are closed and the other switches are open, the diode is in forward operation and the current is dominated by the diode current, as a result of which the photocurrent can no longer be detected.

On the other hand, if the switches Si′ and S2′ are closed and the other switches are open, the bandwidth of the photodiode PD decreases so that only low-frequency signals can be detected.

If, on the other hand, the switches S2 and S2' are (permanently) closed and the other switches are open, Iphoto<Idiode. In this case, mixer 1 is switched off.

Obviously, these explanations also apply to positive currents I 1 , I ₂ , each of which is different from zero.

It should be noted that, of course, if the voltage supplies VI and V2 each provide a non-zero voltage (relative to the small-signal ground potential) that is smaller, the above illustration is equally valid, with the indices to are swapping. Obviously, these explanations also apply to negative currents I 1 , I ₂ , each of which is different from zero.

FIG. 4 shows a further embodiment of the invention. The passive core remains as in Figure 3. However, broadband signals can also be detected if the capacitances are very large, ie if Ci, C2 ->", and the impedances Zi, Z ₂ , Z ₃ , Z4 (eg inductances) have been selected appropriately.

The currents can be converted into voltages using the transimpedance amplifiers TlAi and TIA2. If, on the other hand, power is desired at the output, the voltages can be transformed into power at a specific impedance by means of optional matching networks (at the outputs of the transimpedance amplifiers TlAi and TIA2). Furthermore, the system is not limited to just two TIAs transimpedance amplifiers. Any number of TIAS sensitive to different frequencies can be used. After selecting the appropriate transimpedance amplifier, a channel selection can then take place.

The embodiments according to FIG. 4 permit both broadband and narrowband operation.

The embodiments presented here use an H-bridge in contrast to Gilbert cells or non-linearized components. Furthermore, the systems can be implemented as a broadband system or with channel selection. The system also offers the option of being deactivated.

The electro-optical mixer of the invention comprises an H-bridge which allows an optical signal to be multiplied by an electrical signal directly, without the presence of a transimpedance amplifier. The electro-optical mixer of the invention consumes less power, with less complexity and less noise. The chip area is also reduced by the size of the TIA or the Mach-Zehnder modulator. The bandwidth can be adjusted by using appropriate partial matching networks. The bandwidth can also be influenced by the semiconductor technology used.

If transistors are used as switches Si, S2, Si', S2', it should be sufficient that the voltage only reaches a voltage of >3U _T (=75 mV) compared to the Mach-Zehnder modulator, which is significantly lower than 2-3V.

Claims

Claims tro-optical mixer (1) with electrical output, comprising: • a photodiode (PD) for converting an incident optical signal, • a first connection, • a second connection, • wherein a first power supply (Vi) can be connected to the first connection and a second power supply (V2) can be connected to the second connection, or a first power supply (k) can be connected to the first connection and a second power supply (l ₂ ) can be connected to the second connection, • a connection for a small-signal ground potential for the first voltage supply (Vi) and the second voltage supply (V ₂ ) • a first partial matching network (Z ₂ , Z ₄ ) which is arranged on the anode side of the photodiode (PD), a part of the first partial matching network (Z ₂ ) being switchable (S _{2 ) to the connection for the second voltage supply (V 2 )} can be connected, and wherein another part of the first partial matching network (Z4) can be connected in a switchable manner (S/) to the connection for the small-signal ground potential, • a second sub-matching network (Zi, Z ₃ ), which is arranged on the cathode side of the photodiode (PD), with part of the second sub-matching network (Zi) being switchably (Si) connectable to the connection for the first voltage supply (Vi), and wherein another part of the second partial matching network (Z ₃ ) can be connected in a switchable manner (Si') to the connection for the small-signal ground potential, • wherein the elements of the first partial matching network (Z ₂ , Z4) and the second partial matching network (Zi, Z ₃ ) have an inductive and/or resistive character and/or a capacitive character, • a first capacitive element (Ci), which is arranged on the cathode side of the photodiode (PD), • a second capacitive element (C ₂ ), which is arranged on the anode side of the photodiode (PD), • wherein the first decoupling element (Ci) and the second decoupling element (C ₂ ) have an inductive and/or resistive character and/or a capacitive character, • wherein between the sides of the first decoupling element (C and the second decoupling element (C ₂ )) remote from the photodiode (PD), an electrical output signal can be provided during operation. 2. Electro-optical mixer according to claim 1, characterized in that the electrical output signal is fed to a respective transimpedance amplifier (TlAi, TI A ₂ ). 3. Electro-optical mixer according to claim 1 or 2, characterized in that the switches (Si, S ₂ , Si ', S ₂ ') are designed as any switching element. 4. Electro-optical mixer according to one of the preceding claims, characterized in that the switches (Si, S ₂ , Si ', S ₂ ') are designed as semiconductor switches. 5. Electro-optical mixer according to one of the preceding claims, characterized in that with a suitable switch selection, the circuit can operate as an optical receiver. 6. Electro-optical mixer according to one of the preceding claims, characterized in that the electro-optical mixer can be deactivated by means of the switches (Si, S ₂ , Si', S ₂ '). 7. Electro-optical mixer according to one of the preceding claims, characterized in that the switching positions of the switches (Si, S ₂ , S, S ₂ ') can be controlled by any signal. 8. Electro-optical mixer according to one of the preceding claims, characterized in that the switching positions of the switches (Si, S ₂ , Si ', S ₂ ') can be controlled by an optical signal and / or by an electrical signal and / or by a mechanical signal are. 9. Electro-optical mixer according to one of the preceding claims, characterized in that the elements of the first partial matching network (Z ₂ , Z ₄ ) and the second partial matching network (Zi, Z ₃ ) have an inductive character, the inductive character being generated by coils and/or by lines is provided. 10. Electro-optical mixer according to one of the preceding claims, characterized in that the elements of the first sub-matching network (Z ₂ , Z ₄ ) and the second partial matching network (Zi, Za) have a capacitive character, the capacitive character being provided by capacitors and/or lines. 11. Electro-optical mixer according to one of the preceding claims, characterized in that the system is implemented in semiconductor technology. 12. Electro-optical mixer according to one of the preceding claims, characterized in that the system is implemented with discrete components. 13. Electro-optical mixer according to one of the preceding claims, characterized in that the system can work with any polarized light. 14. Electro-optical mixer according to one of the preceding claims, characterized in that the system can work with purely TE-polarized light and/or with purely TM-polarized light.