Driver Circuit and Method for Driving a Signal
A driver circuit for driving a transmit signal for a line includes a signal amplifier configured to deliver a transmit signal, present at a signal input of the signal amplifier, amplified with a gain to a signal output, a line interface circuit connected between the signal output of the signal amplifier and the line, and a hybrid circuit connected to the line interface circuit, the hybrid circuit configured to suppress the transmit signal and couple a received signal received via the line to a signal input of the signal amplifier to provide impedance synthesis.
This application is a continuation of U.S. application Ser. No. 11/474,636 filed on 26 Jun. 2006, which claims priority to German Patent Application No. 10 2005 030 049.9 filed on 27 Jun. 2005, the content of both applications incorporated herein by reference in their entirety.
TECHNICAL FIELDThe invention relates to a circuit and method for driving a transmit signal which, in particular, can be used in transceivers.
BACKGROUNDIn the driver circuit shown in
From the point of view of the telephone line, the output impedance is:
ZLine=n2(Zcosyn+ZcoEXT),
where the actively synthesized impedance Zcosyn is dependent on the synthesis resistor Rsyn and the feedback resistor Rfb:
The gain of the driver circuit according to the prior art, shown in
Where ZL is the impedance of the transformer as seen from the signal amplifier and wherein Zt is equal to the external terminating impedance ZcoEXT.
If a class-D signal amplifier is used as signal amplifier which supplies an amplified pulse-width-modulated signal, an analogue low-pass filter is usually provided between the signal amplifier output and the transformer in order to filter out a high-frequency switching noise of the amplified transmit signal, produced during the amplification by the class-D signal amplifier. This low-pass filter is also called an OOB (out of band) filter.
In the driver circuit shown in
ZLine=n2(Zcosyn+ZcoEXT),
where the synthesized impedance is dependent on the transfer function Hcos of the low-pass filter:
The gain of the driver circuit is obtained as:
The driver circuit as shown in
The invention provides a driver circuit for driving a transmit signal for a line comprising a signal amplifier configured to deliver a transmit signal, present at a signal input of the signal amplifier, amplified with a gain at a signal output, a line interface circuit connected between the signal output of the signal amplifier and the line, and a hybrid circuit connected to the line interface circuit, the hybrid circuit configured to suppress the transmit signal and couple a received signal received via the line to a signal input of the signal amplifier to provide impedance synthesis.
The invention also provides a driver circuit for driving a transmit signal for a line comprising a signal amplifier configured to deliver a transmit signal, present at a signal input of the signal amplifier, amplified with a gain at a signal output, a transformer having a secondary winding is connected to the line and a primary winding having a first terminal connected to the signal output of the signal amplifier and a second terminal connected to a terminating impedance, and at least one hybrid circuit having a first feedback impedance configured to feed back the first connection of the primary winding to the signal input of the signal amplifier and a second feedback impedance configured to feed back the second connection of the primary winding to the signal input of the signal amplifier.
In one embodiment of the driver circuit according to the invention, the hybrid circuit couples a received signal received via the line.
In one embodiment of the driver circuit according to the invention, the received signal coupled out by the hybrid circuit is added to the transmit signal at a summation node for the purpose of impedance synthesis.
In a further embodiment of the driver circuit according to the invention, the synthesized impedance can be adjusted independently of the gain of the signal amplifier.
In one embodiment of the driver circuit according to the invention, a filter for filtering high-frequency signal disturbances of the amplified transmit signal is provided between the signal amplifier and the transformer.
In a further embodiment of the driver circuit according to the invention, the ratio of impedance values of the two feedback impedances contained in the hybrid circuit is such that the gain is independent of a filter transfer function of the filter.
In one embodiment of the driver circuit according to the invention, the filter is an out-of-band filter.
In one embodiment of the driver circuit according to the invention, the signal amplifier is a class-D signal amplifier which delivers a pulse-width-modulated transmit signal.
In one embodiment of the driver circuit according to the invention, the filter is an analogue low-pass filter for filtering out a high-frequency switching noise of the pulse-width-modulated amplified transmit signal.
In one embodiment of the driver circuit according to the invention, the feedback impedances are formed by resistors.
In one embodiment of the driver circuit according to the invention, the feedback impedances are integrated in the signal amplifier.
In a preferred embodiment of the driver circuit according to the invention, the second feedback loop generates a synthesized line terminating impedance.
In one embodiment of the driver circuit according to the invention, it is of fully differential construction.
The invention also creates a hybrid circuit for a transceiver which couples out a received signal received via a line and adds it to a transmit signal of the transceiver at a summation node for the purpose of impedance synthesis of an output impedance of the transceiver.
The invention also creates a method for driving a transmit signal, in which a transmit signal is amplified and coupled into a line, wherein a received signal received via the line is coupled out and added to the transmit signal for the purpose of impedance synthesis.
In the text which follows, embodiments of the driver circuit according to the invention are described with reference to the attached figures, for explaining features essential to the invention.
As can be seen from
The driver circuit 1 also contains a transformer 12 with a primary winding 12-1 and a secondary winding 12-2. The primary winding 12-1 has a first terminal 13 and a second terminal 14. The first terminal 13 of the primary winding 12-1 of the transformer 12 is connected to the OOB filter 11. The second terminal 14 of the primary winding 12-1 is connected to a terminating impedance 15. At the secondary winding 12-2 of the transformer 12, a line 16, particularly a twisted two-wire telephone line 16, is connected.
The embodiment of the driver circuit 1 shown in
In addition, the driver circuit 1 contains a second feedback loop which feeds the second connection 14 of the primary winding 12-1 back to the first signal input 8 of the operational amplifier 7 via a second feedback impedance 18. In the driver circuit 1 according to the invention, the ratio of the resistance values of the two feedback impedances 17, 18 is dimensioned in such a manner that the gain is independent of the filter transfer function of the OOB filter 11.
As can be seen by comparing
The signal amplifier 2 is preferably formed by a class-D signal amplifier which delivers an amplified pulse-width-modulator transmit signal to the OOB filter 11. The OOB filter 11 is an analogue low-pass filter which filters out the high-frequency disturbances produced during the signal amplification or, respectively, the high-frequency switching noise of the pulse-width-modulated amplified transmit signal in order to ensure, in particular, the spectral power density of the transmit signal demanded by the standard.
The feedback impedances 17, 18 are preferably formed by resistors. These feedback resistors are preferably integrated in the signal amplifier 2. The output impedance, seen by the telephone line 16, of the driver circuit 1 according to the invention is:
Zline=n2·(Zco_syn+Zco_ext),
where the actively synthesized impedance Zcosyn is obtained as follows:
Where Rsyn, is the resistance value of the feedback impedance 18, k·Rsyn is the resistance value of the feedback impedance 17, Rfb is the resistance value of the feedback resistor 9, and ZcoEXT is the impedance of the external terminating impedance.
The gain is then obtained as follows:
if the ratio k between the resistance values of the two feedback impedances 17, 18 is selected in such a manner that
then the gain G is independent of the transfer function HOOB of the filter 11:
In the embodiment of the driver circuit 1 as shown in
The external terminating impedance 15, shown in
In one embodiment, the embodiment is of fully differential construction as is shown in
In the fully differential embodiment according to
By providing an additional feedback loop, the driver circuit 1 thus achieves a situation where the gain is independent of the transfer characteristics of the OBB filter 11 and where no instabilities can occur in the feedback loop.
in the embodiment shown in
is connected between the signal amplifier 20 and the primary winding 12-1 of the transformer 12. The filter 11 shown in
to a summation node provided in the hybrid circuit 21C and added to the signal branched off at the branching node 25. The sum signal is amplified at a further signal amplifier G and applied to the summation node 22.
Claims
1. A driver circuit for driving a transmit signal for a line, comprising:
- a signal amplifier configured to deliver a transmit signal, present at a signal input of the signal amplifier, amplified with a gain to a signal output;
- a transformer having a secondary winding configured to be coupled to the line and a primary winding having a first terminal connected to the signal output of the signal amplifier and a second terminal connected to a terminating impedance; and
- at least one hybrid circuit having a first feedback impedance configured to feed back the first connection of the primary winding to the signal input of the signal amplifier and a second feedback impedance configured to feed back the second connection of the primary winding to the signal input of the signal amplifier.
2. A driver circuit according to claim 1, wherein a received signal received via the line is coupled out by the hybrid circuit.
3. A driver circuit according to claim 2, wherein the received signal coupled out by the hybrid circuit is added to the transmit signal at a summation node for providing impedance synthesis.
4. A driver circuit according to claim 3, wherein the synthesized impedance is adjustable independently of the gain of the signal amplifier.
5. A driver circuit according to claim 1, further comprising a filter between the signal amplifier and the transformer and configured to filter high-frequency signal disturbances of the amplified transmit signal.
6. A driver circuit according to claim 5, wherein a ratio of impedance values of the two feedback impedances contained in the hybrid circuit is such that the gain is independent of a filter transfer function of the filter.
7. A driver circuit according to claim 5, wherein the filter is an out-of-band filter.
8. A driver circuit according to claim 1, wherein the signal amplifier is a class-D signal amplifier configured to deliver a pulse-width-modulated transmit signal.
9. A driver circuit according to claim 7, wherein the filter is an analogue low-pass filter configured to filter a high-frequency switching noise of the pulse-width-modulated amplified transmit signal.
10. A driver circuit according to claim 1, wherein the feedback impedances are formed by resistors.
11. A driver circuit according to claim 1, wherein the driver circuit is of differential construction.
12. A driver circuit according to claim 1, wherein the line is a telephone line.
13. A driver circuit for driving a transmit signal for a telephone line, comprising:
- a signal amplifier configured to amplify a transmit signal, present at a signal input of the signal amplifier, with a gain and deliver the transmit signal to a signal output;
- a filter configured to filter high-frequency signal disturbances of the amplified transmit signal in accordance with a filter transfer function;
- a transformer having a secondary winding configured to be coupled to the telephone line and a primary winding having a first terminal connected to the filter and a second terminal connected to a terminating impedance;
- a first feedback loop configured to feed back the first connection of the primary winding to the signal input of the signal amplifier via a first feedback resistor;
- a second feedback loop configured to feed back the second connection of the primary winding to the signal input of the signal amplifier via a second feedback impedance; and
- wherein a ratio of the resistance values of the two feedback impedances is such that the gain is independent of the filter transfer function of the filter.
14. A driver circuit according to claim 13, wherein the signal amplifier is a class-D signal amplifier configured to deliver a pulse-width-modulated transmit signal.
15. A driver circuit according to claim 14, wherein the filter is an analogue low-pass filter configured to filter a high-frequency switching noise of the pulse-width-modulated amplified transmit signal.
16. A driver circuit according to claim 13, wherein the feedback impedances are formed by resistors.
17. A driver circuit according to claim 13, wherein the second feedback loop is configured to generate a synthesized line terminating impedance.
18. A driver circuit according to claim 13, wherein the driver circuit is of differential construction.
19. A driver circuit for driving a transmit signal for a line, comprising:
- a signal amplifier configured to deliver a transmit signal, present at a signal input of the signal amplifier, amplified with a gain to a signal output;
- a line interface circuit connected between the signal output of the signal amplifier and the line; and
- a hybrid circuit connected to the line interface circuit, the hybrid circuit configured to suppress the transmit signal and couple a received signal received via the line to a signal input of the signal amplifier to provide impedance synthesis.
20. A driver circuit according to claim 19, wherein the driver circuit is of differential construction.
Type: Application
Filed: Nov 16, 2011
Publication Date: Mar 15, 2012
Inventors: Andreas Wiesbauer (Portschach), Sergio Walter (Villach), Alexander Kahl (Landskron), David San Segundo Bello (Villach)
Application Number: 13/297,319
International Classification: H04M 1/00 (20060101);