Feedforward echo cancellation device

Abstract

A feedforward echo cancellation device includes: a first impedance circuit for outputting a first current to a node in response to a transmission current; an echo cancellation current generation circuit for drawing an echo cancellation current from the node; and a second impedance circuit for outputting a second current to the node in response to the transmission current. The communication device includes a programmable gain amplifier. The feedforward echo cancellation device is disposed before the input end of the programmable gain amplifier. The programmable gain amplifier includes a circuit module which is coupled to the echo cancellation current generation circuit and the node. A first impedance value thereof is adjusted based on a system convergence index of a communication device, and the first impedance value is used to determine a gain of the programmable gain amplifier in the communication device. A second impedance value of the second impedance circuit is adjusted correspondingly based on the first impedance value of the circuit module. The node is coupled to the input end of the programmable gain amplifier.

Description

Technical Field

[0001] The present invention relates to a communication system, and more particularly to a feedforward echo cancellation device for a full-duplex communication device. Background Art

[0002] In a full-duplex communication system, signal transmission and reception occur simultaneously. Therefore, the signal received by a receiver in a communication device may include the transmission signal sent by the transmitter of a remote communication device and the echo caused by the transmission signal sent by the local transmitter. To correctly obtain the information to be transmitted by the remote communication device from the received signal, a full-duplex communication device usually relies on an echo cancellation device to cancel the echo in the received signal.

[0003] The principle of an echo cancellation device is to remove the estimated value of the echo signal from the received signal, that is, the echo cancellation signal. The magnitude of the echo signal depends on the impedance encountered by the transmission signal in the output path, and the echo cancellation device will simulate the impedance in the output path through a variable impedance circuit. When the current related to the transmission signal flows through this variable impedance circuit, an echo cancellation signal can be generated. However, since the impedance in the output path includes the cable impedance connected to the remote communication device, the transformer impedance, the printed circuit board trace impedance, the chip package impedance, etc., the variable impedance circuit in the echo cancellation device often cannot accurately simulate the impedance in the output path. As a result, the echo cancellation signal and the echo signal do not match in the high-frequency band, making the echo cancellation device unable to effectively cancel the echo signal in the received signal. Summary of the Invention

[0004] In view of this, one of the objectives of the present invention is to provide an echo cancellation device for canceling the echo caused by the transmission signal in a communication device. Embodiments of the present invention generate a compensation signal to make up for the difference in high-frequency energy between the echo signal and the echo cancellation signal. Moreover, the present invention also dynamically adjusts the generation of the compensation signal according to the change of the system gain, so as to obtain the best echo cancellation effect.

[0005] An embodiment of the present invention provides a feed - forward echo cancellation device for a communication device. The feed - forward echo cancellation device includes: a first impedance circuit, an echo cancellation current generation circuit, and a second impedance circuit. The first impedance circuit is coupled to a node and is configured to output a first current to the node in response to a transmission current; the echo cancellation current generation circuit is coupled to the node and is used to draw an echo cancellation current from the node. The second impedance circuit is coupled to the node and is configured to output a second current to the node in response to the transmission current. The communication device includes a programmable gain amplifier. The feed - forward echo cancellation device is disposed before the input end of the programmable gain amplifier. The programmable gain amplifier includes a circuit module. The circuit module is coupled between the echo cancellation current generation circuit and the node. A first impedance value of the circuit module is adjusted based on a system convergence index of the communication device, and the first impedance value is used to determine a gain of the programmable gain amplifier in the communication device. A second impedance value of the second impedance circuit is adjusted accordingly based on the first impedance value of the circuit module. Wherein, the node is coupled to the input end of the programmable gain amplifier. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 An architecture diagram showing the feed - forward echo cancellation device and an application example according to an embodiment of the present invention.

[0007] Figure 2 Showing the relationship between the signal generated by the feed - forward echo cancellation device according to an embodiment of the present invention and the echo. [[ID=***12]]

[0008] Figures 3 to 5 Showing different implementation aspects of the second impedance circuit in the feed - forward echo cancellation device according to an embodiment of the present invention.

[0009] Figure 6 Showing another implementation aspect of the second impedance circuit in the feed - forward echo cancellation device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0010] In the following content, many specific details are described to provide a thorough understanding of the embodiments of the present invention for the reader. However, those skilled in the art will be able to understand how to implement the present invention in the absence of one or more specific details, or by using other methods or elements or materials, etc. In other cases, well - known structures, materials, or operations are not shown or described in detail, so as to avoid obscuring the core concepts of the present invention.

[0011] As used herein, "an embodiment" means that the particular features, structures, or characteristics described in that embodiment may be included in at least one embodiment of the present invention. Thus, the appearances of "in an embodiment" in various places in this specification are not necessarily all referring to the same embodiment. Furthermore, the aforementioned particular features, structures, or characteristics may be combined in any suitable form in one or more embodiments.

[0012] Please refer to Figure 1 , which shows the architecture diagram of an embodiment of the feedforward echo cancellation device of the present invention. The feedforward echo cancellation device 100 can be used in the proximal communication device 10. The transmitter circuit 12 in the proximal communication device 10 is used to output a transmission signal on the transmission cable 30, and the transmission signal is conducted to the distal communication device 20 through the transmission cable 30. Among them, the transmission signal is driven by the transmission current generation circuit 150, and the transmission current generation circuit 150 may include a current-type digital-to-analog converter for converting the information that the proximal communication device 10 wants to transmit to the distal communication device 20 into an analog signal, that is, the transmission current I TX . The transmission current I TX will be converted into a transmission signal by the transmitter circuit 12. In addition, the echo caused by the transmission signal will be received by the first impedance circuit 110 and the second impedance circuit 120 in the feedforward echo cancellation device 100. In order to avoid affecting the discrimination of the received signal by the proximal communication device 10 and accurately restore the information transmitted by the distal communication device 20, the feedforward echo cancellation device 100 will be used to reduce or eliminate the echo caused by the transmission signal.

[0013] In this embodiment, the impedance of the first impedance circuit 110 is substantially the impedance encountered on the path where the proximal communication device 10 sends the transmission signal to the distal communication device 20. The transmission current I provided by the transmission current generation circuit 150 TX becomes the current I1 after passing through the first impedance circuit 110, and the current I1 can be used to simulate the echo received by the receiver circuit 11. Furthermore, the feedforward echo cancellation device 100 further includes a second impedance circuit 120, a node 140, a transmission current generation circuit 150, and an echo cancellation current generation circuit 160. The second impedance circuit 120 is coupled to the transmission current generation circuit 150, and its impedance value is adjustable. The echo cancellation current generation circuit 160 is coupled to the node 140, and the impedance value on the path from the echo cancellation current generation circuit 160 to the node 140 is also adjustable. The echo cancellation current generation circuit 160 can operate as a current source circuit to extract the echo cancellation current I EC (marked as minus sign) from the node 140. The extracted echo cancellation current I EC has a certain relationship with the transmission current I generated by the transmission current generation circuit 150 TX , so that the echo cancellation current IEC Can match the current I1 as much as possible.

[0014] As described above, the impedance value on the path of the echo cancellation current generation circuit 160 to the node 140 can be affected by the control circuit 15 to a certain extent. The control circuit 15 may include a digital signal processor (not shown). The digital signal processor in the control circuit 15 can judge factors such as the signal-to-noise ratio and / or the echo signal energy magnitude according to the signal output from the programmable gain amplifier circuit 17, and then adjust the echo cancellation current I EC The magnitude, or the impedance on the path of the echo cancellation current generation circuit 160 to the node 140 to a certain extent, so that the echo cancellation current I EC Approaches the current I1 in each frequency band. However, as previously described, there is a mismatch between the current I1 and the echo cancellation current I EC In the high-frequency band, resulting in an unsatisfactory echo cancellation effect. Therefore, the transmission current I generated by the transmission current generation circuit 150 TX Will generate a current I2 after flowing through the second impedance circuit 120. The current I2 can compensate for the energy difference between the echo cancellation current I EC And the current I1 in the high-frequency band (as Figure 2 Shown), so that And the impedance value of the second impedance circuit 120 is also controlled by the control circuit 15.

[0015] On the other hand, the proximal communication device 10 further includes a programmable gain amplifier circuit 17, whose gain is controlled by the control circuit 15. Among them, the programmable gain amplifier circuit 17 includes a circuit module 130 and an amplifier 132. The circuit module 130 has a variable impedance and can be controlled by the control circuit 15. Its specific architecture will be described in detail later. By changing the impedance value of the circuit module 130, the gain of the programmable gain amplifier circuit 17 can be determined. Furthermore, the digital signal processor in the control circuit 15 can analyze the system convergence state for the signal output from the programmable gain amplifier circuit 17 (such as: analyzing according to the signal energy and the signal swing). According to the analysis result, the control circuit 15 selects a suitable gain for the programmable gain amplifier circuit 17 (that is, changes the impedance value of the circuit module 130). The feedforward echo cancellation device 100 is arranged before the input end of the programmable gain amplifier circuit 17. After the feedforward echo cancellation device 100 cancels the echo on the receiving path, the programmable gain amplifier circuit 17 amplifies the signal on the receiving path according to the current gain. When the control circuit 15 selects an appropriate gain for the programmable gain amplifier circuit 17, it will adjust the echo cancellation current I EC The magnitude, so that the echo cancellation current IEC Approach current I1. Then, according to the impedance of circuit module 130, adjust the impedance of the second impedance circuit 120, and make up the echo cancellation current I at node 140 through current I2 EC And the drop in high-frequency energy with current I1.

[0016] Figure 3 Further shows various implementation aspects of the second impedance circuit 120 in an embodiment of the present invention. As shown in the figure, the second impedance circuit 120 can be implemented using a single variable capacitor with a small capacitance value (such as aspect (a)), or can also be implemented using multiple variable capacitors with larger capacitance values connected in series (such as aspects (b) to (e)). The advantage of using multiple variable capacitors with larger capacitance values to implement the second impedance circuit 120 is to reduce the interference of parasitic capacitance. In addition, as Figure 4 Shown, use a C-2C capacitor array to implement, and change the overall impedance value of the second impedance circuit 120 through a switching switch to achieve a specific signal gain. Figure 5 Shows an implementation aspect with better impedance adjustability.

[0017] Figure 6 Shows another implementation aspect of the second impedance circuit 120 of the present invention. As shown in the figure, the second impedance circuit 120 can be implemented by resistor R1, capacitor networks 121, 122, and 123. Resistor R2 can be generally understood as the impedance value of the first impedance circuit 110. Capacitor networks 121 and 122 each have multiple parallel circuit branches, and each circuit branch has a series-connected capacitor and switch. The switch states on these circuit branches will determine the configurations of capacitor networks 121 and 122, so that capacitor networks 121 and 122 present specific equivalent capacitance values. The configuration of capacitor network 121 can determine the gain and bandwidth of the proximal communication device 10 for the received signal. The configuration of capacitor network 122 can determine the coarse gain of the proximal communication device 10 for the received signal. During the operation of the proximal communication device 10, the control circuit 15 will first select a specific gain of the programmable gain amplifier circuit 17. Then, at this specific gain, the control circuit 15 will determine the configurations of capacitor networks 121 and 122 by controlling the switch states to adjust the bandwidth and gain of the second impedance circuit 120. After the configurations of capacitor networks 121 and 122 are determined, capacitor network 123 will be adjusted as the capacitance value of circuit module 130 changes. Among them, in order to avoid the adjustment of capacitor network 122 further affecting the system gain and bandwidth determined by the configuration of capacitor network 121, this embodiment also uses a capacitor C with a low capacitance value relative to the capacitances of other capacitor networks P, ensure that the RC time constant of the circuit before the capacitor network 123 is not affected by the adjustment of the capacitor network 122 and the capacitor network 123. In this way, it can be ensured that the bandwidth determined by the capacitor network 121 will not change due to the adjustment of the capacitor network 122 and the capacitor network 123. Additionally, when the control circuit 15 adjusts the configuration of the capacitor network 121 in order to search for the optimal bandwidth of the system, it may cause a change in the system gain, resulting in the system gain deviating from the optimal gain. Therefore, the control circuit 15 can subsequently compensate for the system gain by adjusting the configuration of the capacitor network 122 to optimize the system gain. In some embodiments of the present invention, it is also possible to implement the adjustable capacitor networks 121 and 122 based on Figures 3 to 5 's architecture.

[0018] Once the control circuit 15 changes the gain of the programmable gain amplifier circuit 17, that is, the capacitances C A1 , C A2 , C W1 and C W2 in the circuit module 130 will be adjusted by the control circuit 15. When the capacitances C A1 , C A2 , C W1 and C W2 in the circuit module 130 change, the control circuit 15 will correspondingly adjust the capacitances C B1 , C B2 , C T1 and C T2 in the capacitor network 123. The capacitance ratio between the capacitances C B1 and C B2 in the capacitor network 123 will be adjusted according to the capacitance ratio between C A1 and C A2 in the circuit module 130, and the capacitance ratio between the capacitances C T1 and C T2 in the capacitor network 123 will be adjusted according to the capacitance ratio between C W1 and C W2 in the circuit module 130. Through such a linkage relationship, it can be ensured the echo cancellation effect that the feedforward echo cancellation device 100 can achieve. It should be noted that in some embodiments of the present invention, the number of capacitors in the capacitor network 123 is not a limitation of the present invention either. In other embodiments, the capacitor network 123 may only include fewer groups of capacitors (where the capacitances C B1 and C B2 can be regarded as a group of capacitors, and the capacitances C T1 and C T2can be regarded as another group of capacitors) or more groups of capacitors. The capacitors of circuit module 130 may also include fewer groups of capacitors (wherein, capacitor C A1 and C A2 can be regarded as a group of capacitors, capacitor C W1 and C W2 can be regarded as another group of capacitors) or more groups of capacitors. When more groups of capacitors are used to implement circuit module 130 and capacitor network 123, the span of gain change can be made smaller to avoid excessive instantaneous gain change and prevent the system from converging. In some embodiments of the present invention, capacitor networks 121 and 122 can also be omitted, and the capacitance value of capacitor network 123 is directly adjusted to obtain the optimal system bandwidth and gain, and the difference between the echo signal and the echo cancellation signal is eliminated as the capacitance value of circuit module 130 changes.

[0019] Furthermore, since control circuit 15 can consider factors such as the external environment, the temperature and state of the system when selecting the gain of programmable gain amplifier circuit 17, it determines the impedance of circuit module 130, and thus determines the gain of programmable gain amplifier circuit 17. Once control circuit 15 reselects the gain of programmable gain amplifier circuit 17, the impedance values on the paths of second impedance circuit 120 and echo cancellation current generation circuit 160 to node 140 will also be adjusted as these factors change.

[0020] In summary, the feedforward echo cancellation device of the present invention compensates for the difference in high-frequency energy between the echo signal and the echo compensation signal through a compensation signal. And during the process of echo cancellation, the compensation signal is fed into the input end (i.e., node 140) of the programmable gain amplifier circuit, so the influence of the programmable gain amplifier circuit on high-frequency energy compensation is effectively excluded. In the embodiments of the present invention, the feedforward echo cancellation device can also optimize the system bandwidth and gain through multiple capacitor networks.

[0021] The above are only the preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope covered by the present invention.

[0022]

Symbol Description

[0023] 10 Near-end communication device

[0024] 11 Receiver circuit

[0025] 12 Transmitter circuit

[0026] 15 Control circuit

[0027] 17 Programmable gain amplifier circuit

[0028] 100 Feedforward echo cancellation device

[0029] 110 First impedance circuit

[0030] 120 Second impedance circuit

[0031] 130 Circuit module

[0032] 140 Node

[0033] 150 Transmission current generation circuit

[0034] 160 Echo cancellation current generation circuit

[0035] 20 Remote communication device

[0036] 30 Transmission cable.

Claims

1. A feedforward echo cancellation device for a communication device, comprising: A first impedance circuit, coupled to a node, for outputting a first current to the node in response to a transmission current; An echo cancellation current generation circuit, coupled to the node, for drawing an echo cancellation current from the node; And A second impedance circuit, coupled to the node, for outputting a second current to the node in response to the transmission current; Wherein the communication device includes a programmable gain amplifier, the feedforward echo cancellation device is disposed before the input end of the programmable gain amplifier, the programmable gain amplifier includes a circuit module, the circuit module is coupled between the echo cancellation current generation circuit and the node, a first impedance value of the circuit module is adjusted based on a system convergence index of the communication device, and the first impedance value is used to determine a gain of the programmable gain amplifier in the communication device, and a second impedance value of the second impedance circuit is adjusted accordingly based on the first impedance value of the circuit module; Wherein when the gain of the programmable gain amplifier is determined, the first impedance value of the circuit module is adjusted according to the determined gain of the programmable gain amplifier; Wherein the node is coupled to the input end of the programmable gain amplifier; And wherein the system convergence index includes signal-to-noise ratio or echo signal energy.

2. The feedforward echo cancellation device according to claim 1, wherein the second impedance circuit further includes a first capacitor network, and a capacitance value of at least one capacitor in the first capacitor network is adjusted along with a capacitance value of at least one capacitor in the circuit module.

3. The feedforward echo cancellation device according to claim 2, wherein the second impedance circuit includes a C-2C capacitor array.

4. The feedforward echo cancellation device according to claim 2, wherein the second impedance circuit further includes a second capacitor network, and an equivalent capacitance value of the second capacitor network determines a bandwidth and a gain of the communication device for a received signal of the communication device.

5. The feedforward echo cancellation device according to claim 4, wherein the second impedance circuit includes a third capacitor network, and an equivalent capacitance value of the third capacitor network determines a rough gain of the communication device for the received signal.

6. The feedforward echo cancellation device according to claim 5, wherein the configuration adjustment of the second capacitor network and the third capacitor network is performed prior to the configuration adjustment of the first capacitor network.

7. The feedforward echo cancellation device according to claim 5, wherein the second capacitor network and the third capacitor network respectively include a plurality of circuit branches, each circuit branch includes a capacitor and a switch connected in series, and the configurations of the second capacitor network and the third capacitor network are respectively determined by the switch states on the circuit branches.

8. The feedforward echo cancellation device according to claim 1, wherein the gain of the programmable gain amplifier is determined according to the signal energy and signal swing of a received signal of the communication device.

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