Amplifier with adaptive feedback

Abstract

The invention provides an amplifier (3) for amplifying an electrical input signal (Vin). The amplifier (3) comprises at least one amplifier stage (31, 32, 33) and at least one feedback loop (34, 35, 36), the feedback loop comprising a variable feedback loop element (37, 38, 39). Each feedback loop (34, 35, 36) is used to feed back a feedback signal from the output of the at least one amplifier stage (31, 32, 33) to an earlier amplifier stage within the amplifier (3). Each feedback loop (34, 35, 36) has a time constant. The time constant has a first value during a first operating mode. In addition, the amplifier (3) comprises a time constant modifier (40), the time constant modifier (40) being used to modify the value of the variable feedback loop element (37, 38, 39) so that during a second operating mode, the time constant of the at least one feedback loop (34, 35, 36) is modified to a second value.

Description

Technical Field

[0001] The present invention relates to an amplifier comprising at least one feedback loop, and in particular to a transimpedance amplifier for optical fiber applications. Background Art

[0002] In optical links, the received optical power can exhibit sudden changes. These changes can cause amplifiers to fully saturate, especially trans-impedance amplifiers (TIA), resulting in a sudden interruption of the received data stream. The duration of this undesirable "blind" period is related to the time constant of one or more control loops, also known as one or more feedback loops in the amplifier.

[0003] For conventional amplifier operation, the time constant of the feedback loop is usually quite high in order to eliminate the undesired behavior. This results in a long blind period after each sudden change in the amplitude of the received optical signal. Summary of the invention

[0004] It is therefore an object of the present invention to provide an amplifier and a method of operating an amplifier which can achieve acceptable amplification results even after an input signal undergoes a sudden change in amplitude.

[0005] This object is achieved by the features of device claim 1 and method claim 15. The dependent claims can be further developed.

[0006] According to a first aspect of the present invention, there is provided an amplifier for amplifying an electrical input signal. The amplifier comprises at least one amplifier stage and at least one feedback loop, wherein the feedback loop comprises a variable feedback loop element. Each feedback loop is used to feed back a feedback signal from the output of the at least one amplifier stage to an earlier amplifier stage within the amplifier. Each feedback loop has a time constant. The time constant has a first value during a first operating mode. In addition, the amplifier comprises a time constant modifier, which is used to modify the value of the variable feedback loop element so that during a second operating mode, the time constant of the at least one feedback loop is modified to a second value. Because the feedback loop has a variable time constant, sudden changes in the amplitude of the input signal may be recovered and the speed is significantly improved.

[0007] Advantageously, the first value may be greater than the second value. This means that, in the first operating mode, the time constant is greater than in the second operating mode. Thus, in the second operating mode, the time constant modifier reduces the time constant, resulting in a shorter reaction time to changes in the input signal.

[0008] More advantageously, the time constant modifier may include: a time constant modification determiner for determining when to switch from the first operation mode to the second operation mode and / or when to switch from the second operation mode to the first operation mode. In addition, the time constant modifier further includes: a time constant modification setter for modifying the value of the variable feedback loop element, thereby modifying the time constant of the at least one feedback loop according to the determination result of the time constant modification determiner. This facilitates the implementation of the amplifier in a very simple manner.

[0009] Advantageously, the time constant modification determiner may include an amplitude change determiner for determining an amplitude change of the electrical output signal of the amplifier. The time constant modification determiner is used to determine when to switch from the first operating mode to the second operating mode and / or when to switch from the second operating mode to the first operating mode based on the amplitude change of the electrical output signal determined by the amplitude change determiner. Using the output signal of the amplifier facilitates detecting when to switch between two operating modes in a very simple manner.

[0010] More advantageously, the amplitude change determiner may comprise an input amplitude change estimator for estimating the amplitude change of the electrical input signal based on the amplitude change of the electrical output signal. The time constant modification determiner is further configured to determine when to switch from the first operating mode to the second operating mode and / or when to switch from the second operating mode to the first operating mode based on the estimated amplitude change of the electrical input signal. This facilitates particularly accurate determination of when to switch between operating modes.

[0011] More advantageously, the time constant modification determiner may be configured to determine the change from the first operation mode to the second operation mode after the amplitude change of the electrical input signal or the electrical output signal of the amplifier is greater than a first amplitude threshold during a first preset time period, which is advantageous for accurately determining when to switch from the first operation mode to the second operation mode.

[0012] The time constant modification determiner is further configured to determine the change from the second operation mode to the first operation mode after a second preset time period has passed after the change from the first operation mode to the second operation mode, which is advantageous for accurately determining the end time of the rapid amplitude change and the time to return to the normal operation mode (which may be the first operation mode).

[0013] The second preset time period may be greater than the first preset time period. This ensures that the feedback loop has a chance to fully utilize the second operating mode before switching back to the first operating mode.

[0014] Advantageously, the amplitude change determiner may include a glitch determination circuit for determining the amplitude change as a glitch if the duration of the amplitude change determined by the amplitude change determiner is less than a glitch duration threshold. The time constant modification determiner is further configured to ignore the amplitude change determined as a glitch by the glitch determination circuit. This ensures that very brief changes in amplitude do not trigger the second operating mode.

[0015] The at least one variable feedback loop element may include: at least one variable loop element. The time constant modification setter is also used to: change the value of the at least one variable circuit element of the at least one variable feedback loop element. This facilitates implementing the time constant modification setter in a very simple manner.

[0016] The at least one variable circuit element is a memoryless circuit element. This facilitates the realization of the variable circuit element in a very simple manner.

[0017] The at least one variable circuit element may be a variable ohmic resistor or a variable capacitor. This facilitates realizing the variable circuit element in a very simple manner.

[0018] Further advantageously, the amplifier may comprise: a plurality of feedback loops, wherein each feedback loop is used to feed back a different feedback signal to an early amplifier stage within the amplifier, each feedback loop having a variable feedback loop element, each feedback loop having an independent time constant, the independent time constant having an independent first value during the first operating mode. The time constant modifier is further used to modify the value of the variable feedback loop element of the plurality of feedback loops, so that during the second operating mode, the time constants of the plurality of feedback loops are respectively modified to independent second values. Thus, a particularly accurate amplifier may be achieved.

[0019] According to a second aspect of the present invention, there is provided a system comprising an optical input, a photoelectric converter and an amplifier as described above. The optical input is used to receive an optical input signal. The photoelectric converter is used to convert the optical input signal into the electrical input signal. The amplifier is used to amplify the electrical input signal. This is advantageous in that the optical input signal can be amplified very accurately without changing the amplitude.

[0020] According to a third aspect of the present invention, there is provided a method for operating an amplifier for amplifying an electrical input signal. The method comprises: amplifying the electrical input signal using at least one amplifier stage; feeding back at least one feedback signal from the output of the at least one amplifier stage to an early amplifier stage using a variable feedback loop element, wherein the resulting feedback loop has a time constant, and the time constant has a first value during a first operating mode; modifying the value of the variable feedback loop element, thereby modifying the time constant of the at least one feedback loop to a second value during a second operating mode. Since the feedback loop has a variable time constant, a sudden change in the amplitude of the input signal may be recovered, and the speed is significantly improved.

[0021] It is therefore an object of the present invention to provide an apparatus and a method that allow at least one user to perceive directional audio information while keeping disturbance to others to a minimum.

[0022] Generally, it should be noted that all devices, equipment, elements, units and devices described in the present application, etc. can be implemented by software or hardware elements or any combination thereof. In addition, the device can be a processor or can include a processor, and the functions of the elements, units and devices described in the present application can be implemented in one or more processors. The steps performed by the various entities described in the present application and the functions to be performed by the various entities described are intended to refer to each entity for performing each step and function. Although in the description of the following specific embodiments, the specific functions or steps performed by the general entity are not reflected in the description of the specific elements of the entity performing the specific steps or functions, it should be clear to the technician that these methods and functions can be implemented in respective hardware or software elements or any combination thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention is described in detail below in conjunction with embodiments of the present invention with reference to the accompanying drawings, in which

[0024] Figure 1 An exemplary multi-stage amplifier is shown;

[0025] Figure 2 shows input signals and resulting loop control variables in an exemplary amplifier;

[0026] Figure 3 A first embodiment of the amplifier provided by the first aspect of the present invention is shown;

[0027] Figure 4 shows an exemplary input signal and an exemplary loop control variable in a second embodiment of the amplifier provided by the first aspect of the present invention;

[0028] Figure 5 shows details of a third embodiment of the amplifier provided by the first aspect of the present invention;

[0029] Figure 6 shows details of a fourth embodiment of the amplifier provided by the first aspect of the present invention;

[0030] Figure 7 shows details of a fifth embodiment of the amplifier provided by the first aspect of the present invention;

[0031] Figure 8 shows details of a sixth embodiment of the amplifier provided by the first aspect of the present invention;

[0032] Fig. 9 The system embodiment provided by the second aspect of the present invention is shown;

[0033] Fig.10 An embodiment of the method provided in the third aspect of the present invention is shown in a flow chart. DETAILED DESCRIPTION

[0034] first, Figure 1 and Figure 2 The disadvantages of the exemplary amplifier are shown. Figure 3 The main structure and functions of an amplifier embodiment of the present invention are shown and described. Figure 4 The functioning of an embodiment of the amplifier of the present invention is described in more detail with respect to the signal aspects of the amplifier. Figures 5 to 9 Different embodiments of the amplifier according to the invention are described. Finally, Fig.10 The detailed functions of the method embodiment of the present invention are shown. Similar entities and reference numerals in different figures have been partially omitted.

[0035] A transimpedance amplifier (TIA) for optical communications is a radiofrequency (RF) analog device that amplifies one or more input signal currents generated in one or more photodiodes of an optoelectronic converter. The following describes a differential input case and a non-differential case.

[0036] Modern TIAs embed several functions. However, the present invention is not limited to TIAs. Figure 1A block diagram of a typical integrated TIA is shown. The core part is the RF chain 10, which is usually designed as a cascade of several RF blocks, also called amplifier stages 11, 12, 13. In order to control the correct operation of the RF part 10, several control loops 14, 15, 16 are usually implemented. The input signal Vin is the photodiode output signal of the previous photoelectric converter, not shown here. Vin is a high-speed signal current superimposed on a considerable direct current (DC) component. This DC component has no information content and may damage the normal TIA operation if it is not cancelled. Therefore, this unwanted current contribution factor should be cancelled at the TIA input.

[0037] To achieve this function, the TIA has an input DC current loop 14, such as Figure 1 As shown. The loop 14 acts directly on the input pin that absorbs the DC current content of the photodiode current. The loop 14 includes a loop element 17, which in this example is an ohmic resistor connected in series and a capacitor connected in parallel to ground.

[0038] The second loop 15 eliminates the DC offset voltage at the output of the TIA. The DC offset is the result of differential path mismatch and is inevitably related to the accuracy of the integration process. The output node is connected to a sensing module, also called loop element 18, i.e. an integrator. In this example, the loop element 18 also includes an ohmic resistor connected in series and a capacitor connected in parallel to ground. The correction signal is sent to one or more amplifier stages 11, 12, 13 of the RF chain. The loop element 18 controls the residual offset at the output of the TIA, but the loop element 18 has an important impact on the transfer function of the block. In fact, considering the input-output transfer function, the loop produces a high-pass frequency shape. This shape leads to an important conclusion that the offset compensation circuit not only suppresses unnecessary offsets at the output of the TIA, but also attenuates low-frequency components of the input signal Vin from the photodiode. This high-pass filtering should be carefully considered because it may cause inter-symbol interference, reducing the performance of the optical link.

[0039] The voltage swing of the signal at the output of the TIA should be controlled and usually precisely determined. To ensure this function, a third loop 16 is built around the RF chain 10. This control loop is called an automatic gain control loop (AGC), and usually senses the output line of the TIA: the loop element (i.e., the AGC block 19) generates a control signal, which is fed to one or more RF blocks 11, 12, 13. And, in this example, the loop element 19 includes an ohmic resistor connected in series and a capacitor connected in parallel to ground.

[0040] Advantageously, the design includes a variable gain feature that allows the gain of the RF block to be adjusted to set the desired amplitude of the output signal voltage Vout.

[0041] As mentioned above, the DC offset compensation loop 14 should have a very small bandwidth in order not to adversely affect the inter-symbol interference (ISI) of the output signal Vout. Similar considerations can be applied to the input DC current loop 15. The bandwidth of the AGC is usually larger than the DC control loop, but this loop 16 may also be very slow from a data link perspective.

[0042] Each feedback loop 14, 15, 16 has a time constant. These time constants are defined by the components of the respective feedback loop 14, 15, 16. In particular, the values ​​of the feedback loop elements 17, 18 and 19 influence these time constants. In the present example, advantageously, the feedback loop elements 17, 18, 19 are integrators or low-pass filters. The time constant is greatly influenced by the characteristics of these integrators or low-pass filters. However, the time constant is also influenced by another amplifier component part of the respective feedback loop 14, 15, 16, such as the amplifier stage 11, 12, 13. The time constant also corresponds to the bandwidth of the respective feedback loop, in particular, the time constant is the inverse of the bandwidth.

[0043] Figure 2 The time response of the TIA is qualitatively shown when the input optical power undergoes a large sudden change.

[0044] The time evolution of the system is described below, focusing on 4 key instances:

[0045] T1: The input optical power changes suddenly. The RF chain 10 of the TIA responds quickly due to its ultra-large bandwidth. It can be said that the change in the power of the input signal Vin is almost accompanied by the change in the output signal Vout. If the input optical power changes greatly, the output signal may be completely unbalanced and reach full saturation. This unwanted situation will cause the data flow to be interrupted. Figure 2 The lower part of FIG. 1 also shows the qualitative behavior of the loop control variable. Since the time constants of the feedback loops 14, 15, and 16 are large and change very slowly, the time interval to reach the end of the transient state may be quite long.

[0046] T2 represents the end of the time transient of the loop control variable. From this moment on, the control loop reaches equilibrium and the system is in a stable state. After T2, normal operation is restored and the TIA can again amplify the signal current from the photodiode in an optimal way.

[0047] T3: The input optical power undergoes a second mutation, which is opposite to the previous mutation. Similarly, in this transition, the RF chain 10 of the TIA changes almost instantaneously following the change of the input signal. If the input optical power changes greatly, the output signal can reach saturation, resulting in interruption of the data flow. Figure 2 The lower part of the graph also shows the qualitative behavior of the loop control variable. Since the time constant is large and changes very slowly, the time interval to reach the end of the transient can be quite long.

[0048] T4 represents the end of the time transient of the loop control variable. From this moment on, the control loop reaches equilibrium and the system is in a stable state.

[0049] From a data link perspective, the time intervals between T1 and T2 and between T3 and T4 can be very critical. Sudden changes in input optical power can saturate the TIA output, resulting in "blind" intervals in the data link. Of course, these events can be very critical and the "blind time" of the system should be minimized.

[0050] The present invention solves the problems that may arise from input power variations and adds specific functions to limit the impact of saturation. Figure 3 A block diagram showing variations on the basic amplifier.

[0051] The amplifier 3 of the present invention comprises an RF chain 30, which comprises a first amplifier stage 31 connected to a second amplifier stage 32, and the second amplifier stage 32 is connected to a third amplifier stage 33. The output end of the first amplifier stage 31 is connected to a feedback loop element 37, and the feedback loop element 37 is connected to the input end of the amplifier stage 31. The amplifier stage 31 and the feedback loop element 37 form a feedback loop 34.

[0052] The output terminal of the third amplifier stage 33 is connected to a feedback loop element 38, which is connected to control input terminals of the amplifier stages 31, 32 and 33. The amplifier stages 31 to 33 and the feedback loop element 38 form a second feedback loop 35.

[0053] Furthermore, the output terminal of the third amplifier stage 33 is connected to a feedback loop element 39, which is connected to the control input terminals of the amplifier stages 31 to 33. The feedback loop element 39 and the amplifier stages 31 to 33 form another feedback loop 36.

[0054] For example, the feedback loop 34 may correspond to Figure 1 The input DC current loop 14. For example, the feedback loop 35 may correspond to Figure 1 The DC offset compensation loop 15. For example, the feedback loop 36 may correspond to Figure 1 Automatic gain control loop 16.

[0055] Furthermore, the amplifier 3 comprises a time constant modifier 40 which is connected to the output of the third amplification stage 33 and controls the inputs of the variable feedback loop elements 37 , 38 and 39 .

[0056] An input signal Vin is provided to the input terminal of the first amplifier stage 31. The input signal Vin is amplified by the first amplifier stage 31 and then amplified by the second amplifier stage 32. The resulting signal is then passed to the third amplifier stage 33, which performs final amplification to generate an output signal Vout. Feedback loops 34, 35 and 36 feed back respective feedback signals to the early amplifier stages during amplification, optimizing the function of the amplifier 3.

[0057] Each feedback loop 34, 35 and 36 has a time constant. The time constants of the different feedback loops 34 to 36 are independent of each other. Figure 1 As shown, during a first operating mode corresponding to a normal operating mode, each time constant of the feedback loops 34 to 36 has a first value. It should be noted that these first values ​​of the different time constants are not necessarily the same, but are independent.

[0058] The time constant modifier 40 determines when to switch from the first operation mode to the second operation mode, wherein the time constant of the feedback loop 34-36 is changed. In particular, each feedback loop element 37, 38, 39 has at least one variable circuit element to perform the above process, the value of which can be set by the time constant modifier 40. By changing the value of the variable circuit element, the time constant modifier 40 changes the time constant, thereby switching from the first operation mode to the second operation mode.

[0059] In the second operation mode, the time constant of the feedback loop 34 to 36 is significantly reduced relative to the first operation mode, resulting in a significantly faster response speed, so that the amplitude jump of the output signal is restored. The time constant modifier 40 determines when to switch from the first operation mode to the second operation mode based on the output signal Vout of the amplifier 3. However, optionally, an additional or alternative connection to the input signal Vin can also be realized.

[0060] In particular, the time constant modifier 40 may include a MIN / MAX monitor. The amplitude of the output signal extracted by the amplitude detector is checked by the MIN / MAX monitor. The MIN / MAX monitor compares the value of the amplitude information with some thresholds to control whether the output signal Vout of the amplifier is within the correct amplitude range. Typically, the MIN / MAX monitor has a lower threshold and an upper threshold, and controls whether the output amplitude is within the expected range.

[0061] Furthermore, the time constant modifier 40 may include a flip-flop that generates a logic signal to report the undesirable condition if the amplitude of the output signal Vout exceeds a desired range.

[0062] It is important to note that all core blocks of the control loops 34 to 36 have a new feature: bandwidth programmability. This can be achieved by at least one variable circuit element in each of the control loop elements 37 to 39. As mentioned above, all control loop elements can be integrators consisting of ohmic resistors and capacitors.

[0063] Based on these assumptions, the behavior of the amplifier 3 switching between the first operating mode and the second operating mode can be analyzed. If the amplitude of the output signal Vout is within the target range, the control loops 34 to 36 are in the first operating mode, also called normal mode, and no mode switching is triggered. In contrast, if the amplitude of the output signal Vout moves beyond the desired control range, the second operating mode, also called shift mode, is enabled. It should be noted that exceeding the control range of the amplitude of the output signal voltage Vout is an indication of a sudden large power change of the input signal Vin.

[0064] Once the second operating mode is triggered, the system will change its dynamic behavior. Figure 3 As schematically shown, the time constant modifier 40 acts on the feedback loop elements 37 to 39. Thus, the time constant modifier 40 reduces the time constant of the feedback loops 34 to 36 whenever the output signal Vout moves out of the desired amplitude range.

[0065] Based on the previous description, we can further analyze the system, the second mode of operation, and distinguish the time / frequency response of the control loop:

[0066] If the output signal Vout is within the expected amplitude range, the control loops 34 to 37 are in the first operating mode. The bandwidth of the control loops is typically very low and the time constants are set so as not to degrade the quality of the received signal.

[0067] If the output signal Vout is outside the expected amplitude range, the second operating mode is triggered. In this case, the amplifier 3 is not working properly, usually due to the rapid change of the input signal Vin power, the output voltage swing is not set correctly. This situation represents an undesirable situation. Therefore, the system reacts quickly and restores normal function. In order to speed up the transient, the time constants of all control loops are reduced by the time constant modifier 40, resulting in a fast recovery of the control loops 34 to 36.

[0068] Figure 4 The time response of the amplifier is qualitatively shown when a large sudden change in input optical power occurs.

[0069] like Figure 2 As shown, the analysis of the time evolution is as follows, focusing on the key moments:

[0070] T1: The input optical power changes suddenly. The RF chain 30 of the amplifier 3 changes almost instantaneously following the change of the input signal Vin. If the input optical power changes greatly, the output signal Vout can reach saturation, resulting in interruption of the data flow. This abnormal situation is detected by the time constant modifier 40 and proves to be in the second operating mode. Figure 4 The lower part of FIG. 1 shows the qualitative behavior of the loop control variables. Since the second operation mode is enabled, the feedback loops 34 to 36 recover quite quickly, allowing the system to quickly enter the normal operation mode.

[0071] T2 represents the end of the time transient of the loop control variable. The output swing of amplifier 3 returns to the required range and the second operation mode is released. From this moment on, the control loop returns to the first operation mode and its normal time constant, and the system is in a stable state.

[0072] T3: The input optical power undergoes a second sudden change, which is opposite to the previous sudden change. The RF chain 30 of the amplifier 3 changes almost instantaneously following the change of the input signal Vin. If the input optical power changes greatly, the output signal can reach saturation, resulting in interruption of the data flow. This abnormal situation is detected by the time constant modifier 40 and proves to be in the second operating mode. Figure 4 The lower part of FIG. 1 shows the qualitative behavior of the loop control variables. Since the second operation mode is enabled, the feedback loops 34 to 36 recover quite quickly, allowing the system to quickly enter the normal operation mode.

[0073] T4 represents the end of the time transient of the loop control variable. The output swing of the amplifier returns to the required range and the second operation mode is released. From this moment on, the feedback loop 34 to 36 returns to the first operation mode and its normal time constant, and the system is in a stable state.

[0074] and Figure 2 The time evolution described in Figure 4 The benefits of the second operating mode are very clear when compared to the time evolution described in . From a system point of view, the critical intervals are between T1 and T2 and between T3 and T4. It is clear that the introduction of the second operating mode significantly shortens these critical time intervals, resulting in an overall improvement in the dynamic performance of the amplifier.

[0075] Figure 5Detail of another embodiment of the amplifier of the present invention is shown. Here, the internal workings of the time constant modifier 40 are shown. The time constant modifier 40 comprises a time constant modification determiner 41 connected to a time constant modification setter 42. The time constant modification determiner determines when to switch from the first operating mode to the second operating mode and / or when to switch from the second operating mode to the first operating mode. The time constant modification setter 42 modifies Figure 3 The values ​​of the variable feedback loop elements 37 to 39.

[0076] Advantageously, the time constant modification determiner 41 determines a change from the first operation mode to the second operation mode after a change in the amplitude of the electrical input signal Vin or the electrical output signal Vout of the amplifier 3 is greater than a first amplitude threshold value during a first preset time period. The first preset time period ensures that the amplitude change is so fast that a change to the second operation mode is actually required. If the amplitude transition occurs gradually over a period longer than the first preset time period, there is no need to change the time constant, because the conventional time constant can handle the gradual amplitude transition without the amplifier 3 saturating.

[0077] Advantageously, after changing from the first operation mode to the second operation mode, the time constant modification determiner 41 determines the change from the second operation mode to the first operation mode after a second preset time period has passed. Reverting to the first operation mode ensures optimal amplifier performance. Doing so only after a second preset time period has passed ensures that the feedback loops 34 to 36 have sufficient time to handle the amplitude conversion and recovery.

[0078] The second preset time period is greater than the first preset time period. This optional function also facilitates recovery.

[0079] It should be noted that the variable feedback loop elements 37 to 39 each include at least one variable loop element. The variable circuit element may be a variable ohmic resistor, a variable capacitor or a variable inductor. Optionally, a variable ohmic resistor is used. In addition, other variable circuit elements may be used, such as a time delay element or a phase shifter.

[0080] Furthermore, the amplifier may advantageously include not only one feedback loop but multiple feedback loops, such as Figure 3 However, the amplifier may include only a single feedback loop or a different number of feedback loops.

[0081] Figure 61 shows further details of another embodiment of the amplifier of the present invention. The figure shows the internal operation of the time constant modification determiner 41. In this embodiment, the time constant modification determiner 41 includes an amplitude change determiner 43. The amplitude change determiner 43 determines whether an amplitude change has occurred based on the amplitude of the output signal Vout of the amplifier 3. Switching from the first operating mode to the second operating mode and from the second operating mode to the first operating mode is determined based on the amplitude transition detected by the amplitude change determiner 43.

[0082] Figure 7 Another advantageous embodiment is shown in FIG. The internal operation of the amplitude variation determiner 43 is shown. The amplitude variation determiner 43 comprises an input amplitude variation estimator 44. The estimator 44 estimates the variation of the input signal Vin based on the output signal Vout. When to switch from the first operation mode to the second operation mode and / or when to switch from the second operation mode to the first operation mode is determined based on the estimated input signal variation provided by the input amplitude variation estimator 44.

[0083] also, Figure 8 Another embodiment of the amplifier provided by the first aspect of the present invention is shown. The internal operation of the amplitude change determiner 43 is shown in the figure. The amplitude change determiner 43 includes a glitch detection circuit 45. The glitch detection circuit 45 determines whether the determined amplitude change is actually a glitch. This is done by comparing the duration of the amplitude change with the glitch duration threshold. If the duration of the amplitude change is less than the glitch duration threshold, the amplitude change is considered to be a glitch. The amplitude change determiner 43 then ignores the amplitude change. Then, the operating mode switching is not performed based on this amplitude change, and the amplitude change is determined to be a glitch.

[0084] also, Fig. 9 An embodiment of the system provided by the second aspect of the present invention is shown. The system 7 comprises an optical input terminal 5 connected to a photoelectric converter 6, and the photoelectric converter 6 is connected to an amplifier 3. The amplifier 3 corresponds to the amplifier described above. An optical input signal Oin is provided to the optical input terminal 5. The optical input signal is converted into an electrical input signal Vin by the photoelectric converter 6. The amplifier 3 amplifies the electrical input signal Vin and generates an electrical output signal Vout. For the operation of the amplifier 3, please refer to the previous description.

[0085] Fig.10An embodiment of the operating method of the amplifier provided by the third aspect of the present invention is shown. In a first step 100, an electrical input signal is amplified using at least one amplifier stage of the amplifier. In a second step 101, at least one feedback signal is fed back from the output of at least one amplifier stage to an earlier amplifier stage of the amplifier. For this purpose, a variable feedback loop element is used. The feedback loop has a feedback loop time constant. The time constant has a first value during a first operating mode. In a third step 102, the value of the variable feedback loop element is modified so that during a second operating mode, the time constant of at least one feedback loop is modified to a second value. Steps 100 to 102 are repeated continuously.

[0086] It should be noted that the different aspects of the present invention are closely related to each other. Therefore, all explanations about different aspects are applicable to other aspects and can be interchanged.

[0087] The invention is not limited to the examples described, and in particular not to a specific number or type of feedback loops. The invention discussed above can be applied to many different types of feedback loops in amplifiers. The features of the exemplary embodiments can be used in any advantageous combination.

[0088] The present invention is described herein in conjunction with various embodiments. However, those skilled in the art can understand and obtain other variations of the disclosed embodiments by practicing the present invention, studying the drawings, the present invention and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and "one" does not exclude multiple elements or steps. A single processor or other unit can meet the functions of several items described in the claims. The listing of certain measures in generally different dependent claims does not mean that a combination of these measures cannot be effectively used. The computer program may be stored or distributed in a suitable medium, such as an optical storage medium or solid-state medium provided together with other hardware or as part of other hardware, and may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems.

Claims

1. An amplifier (3) for amplifying an electrical input signal (Vin), characterized in that include: - at least one amplifier stage (31, 32, 33), - at least one feedback loop (34, 35, 36) comprising a variable feedback loop element (37, 38, 39), wherein each feedback loop (34, 35, 36) is used to feed back a feedback signal from an output of the at least one amplifier stage (31, 32, 33) to an earlier amplifier stage within the amplifier (3), each feedback loop (34, 35, 36) having a time constant having a first value during a first operating mode; - a time constant modifier (40) for modifying the value of the variable feedback loop element (37, 38, 39) so that during a second operating mode, the time constant of the at least one feedback loop (34, 35, 36) is modified to a second value to shorten the time period for the output of the amplifier to reach saturation, the first value being greater than the second value.

2. The amplifier (3) according to claim 1, characterized in that The time constant modifier (40) comprises: - a time constant modification determiner (41) for determining when to switch from the first operating mode to the second operating mode and / or when to switch from the second operating mode to the first operating mode; - a time constant modification setter (42) for modifying the value of the variable feedback loop element (37, 38, 39) so as to modify the time constant of the at least one feedback loop (34, 35, 36) according to the determination result of the time constant modification determiner (41).

3. The amplifier (3) according to claim 2, characterized in that The time constant modification determiner (41) comprises: an amplitude change determiner (43) for determining an amplitude change of an electrical output signal (Vout) of the amplifier (3); The time constant modification determiner (41) is used to determine when to switch from the first operation mode to the second operation mode and / or when to switch from the second operation mode to the first operation mode according to the amplitude change of the electrical output signal (Vout) determined by the amplitude change determiner (43).

4. The amplifier (3) according to claim 3, characterized in that The amplitude change determiner (43) comprises: an input amplitude change estimator (44) for estimating the amplitude change of the electrical input signal (Vin) according to the amplitude change of the electrical output signal (Vout); The time constant modification determiner (41) is used to determine when to switch from the first operation mode to the second operation mode and / or when to switch from the second operation mode to the first operation mode according to the estimated amplitude change of the electrical input signal (Vin).

5. The amplifier (3) according to claim 3 or 4, characterized in that The time constant modification determiner (41) is used to determine a change from the first operation mode to the second operation mode after the amplitude change of the electrical input signal (Vin) or the electrical output signal (Vout) of the amplifier (3) is greater than a first amplitude threshold during a first preset time period.

6. The amplifier (3) according to claim 5, characterized in that The time constant modification determiner (41) is used to determine a change from the second operation mode to the first operation mode after a second preset time period has passed after the change from the first operation mode to the second operation mode.

7. The amplifier (3) according to claim 6, characterized in that The second preset time period is greater than the first preset time period.

8. The amplifier (3) according to claim 3 or 4, characterized in that The amplitude change determiner (43) comprises: a glitch determination circuit (45) for determining the amplitude change as a glitch when the duration of the amplitude change determined by the amplitude change determiner (43) is less than a glitch duration threshold; The time constant modification determiner (41) is used to ignore the amplitude change determined as a glitch by the glitch determination circuit (45).

9. The amplifier (3) according to claim 2, characterized in that The at least one variable feedback loop element (37, 38, 39) comprises at least one variable loop element; The time constant modification setter (42) is used to change the value of the at least one variable circuit element of the at least one variable feedback loop element (37, 38, 39).

10. The amplifier (3) according to claim 9, characterized in that The at least one variable circuit element is a memoryless circuit element.

11. The amplifier (3) according to claim 9, characterized in that The at least one variable circuit element is a variable ohmic resistor or a variable capacitor.

12. The amplifier (3) according to claim 1, characterized in that The amplifier (3) comprises a plurality of feedback loops (34, 35, 36), wherein each feedback loop is used to feed back a different feedback signal to an early amplifier stage within the amplifier (3), each feedback loop having a variable feedback loop element (37, 38, 39), each feedback loop having an independent time constant, the independent time constant having an independent first value during a first operating mode; The time constant modifier (40) is used to modify the values ​​of the variable feedback loop elements (37, 38, 39) of the plurality of feedback loops (34, 35, 36), thereby modifying the time constants of the plurality of feedback loops (34, 35, 36) to independent second values ​​respectively during the second operation mode.

13. A system (7), characterized in that comprising an optical input terminal (5), a photoelectric converter (6) and an amplifier (3) according to any one of claims 1 to 12, Wherein, the optical input end (5) is used to receive an optical input signal (Oin); The photoelectric converter (6) is used to convert the optical input signal (Oin) into the electrical input signal (Vin); The amplifier (3) is used to amplify the electrical input signal (Vin).

14. A method for operating an amplifier (3) for amplifying an electrical input signal (Vin), characterized in that The method comprises: - amplifying (100) the electrical input signal (Vin) using at least one amplifier stage (31, 32, 33); - feeding back (101) at least one feedback signal from an output of said at least one amplifier stage (31, 32, 33) to an earlier amplifier stage using a variable feedback loop element (37, 38, 39), wherein the resulting feedback loop (34, 35, 36) has a time constant having a first value during a first operating mode; - modifying (102) the value of the variable feedback loop element (37, 38, 39) so that during a second operating mode, the time constant of the at least one feedback loop (34, 35, 36) is modified to a second value to shorten the time period for the output of the amplifier to reach saturation, the first value being greater than the second value.

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