Control circuit for controlling a DC supply voltage for a terminal
View Patent ↗A control device for controlling a supply voltage which can be switched between a constant line current operation and a constant line voltage operation, wherein a line current, which consists of a direct current for supplying the terminal and of an alternating current for transmitting information, flows via a subscriber line of a terminal, comprising a sensing circuit for sensing an analogue input voltage dependent on the line current, a subtractor which, in the constant line current operation, subtracts an analogue feedback voltage dependent on an adjustable nominal direct-current value from the sensed input voltage for generating an analogue difference voltage, an analogue/digital converter for converting the generated analogue difference voltage into a digital difference voltage value, a digital low-pass filter for filtering a sequence of control error values out of the generated sequence of difference voltage values, a controller for generating a control value in dependence on the filtered-out sequence of control error values, and comprising a first digital/analogue converter which, in the constant line current operation, converts the control value in each case generated by the controller into the analogue direct voltage for supplying the terminal.
1. A control device for controlling a supply voltage which can be switched between a constant line current operation and a constant line voltage operation, wherein a line current, which consists of a direct current for supplying the terminal and of an alternating current for transmitting information, flows via a subscriber line of a terminal, comprising:
(a) a sensing circuit configured to sense an analogue input voltage (V SENSE ) dependent on the line current;
(b) a subtractor which, in the constant line current operation, is configured to subtract an analogue feedback voltage dependent on an adjustable nominal direct-current value from the sensed input voltage for generating an analogue difference voltage;
(c) an analogue/digital converter configured to convert the generated analogue difference voltage into a digital difference voltage value;
(d) a digital low-pass filter configured to filter a sequence of control error values out of the generated sequence of difference voltage values;
(e) a controller configured to generate a control value in dependence on the filtered-out sequence of control error values;
(f) a first digital/analogue converter which, in the constant line current operation, is configured to convert the control value in each case generated by the controller into an analogue direct voltage for supplying the terminal; and
(g) a second digital/analogue converter configured to convert the nominal direct-current value into the analogue feedback voltage in the constant line current operation.
2. The control device according to claim 1 , wherein a digital adder is provided which is configured to add the nominal direct-current value to the filtered-out sequence of control error values to form a sequence of aggregate current values.
3. The control device according to claim 2 , wherein a first comparator is provided which is configured to compare the sequence of aggregate current values with a predetermined adjustable direct-current threshold value and, as soon as an aggregate current value drops below the direct-current threshold value, switch the control device from the constant line current operation to the constant line voltage operation.
4. The control device according to claim 1 , wherein the analogue/digital converter is a sigma/delta analogue/digital converter.
5. The control device according to claim 1 , wherein the controller is a PID controller.
6. The control device according to claim 5 , wherein the PID controller is configured to receive a value of zero as input value as long as a second comparator finds that the sequence of control error values is below a predetermined tolerance threshold value.
7. The control device according to claim 6 , wherein the PID controller is configured to receive the filtered-out sequence of control error values as sequence of input values as soon as the second comparator finds that the sequence of control error values exceeds the predetermined tolerance threshold value.
8. The control device according to claim 1 , wherein, in the constant line current operation, the second digital/analogue converter is configured to convert the control value delivered by the controller into the analogue feedback voltage.
9. The control device according to claim 1 , wherein, in the current line current operation, the first digital/analogue converter is configured to convert a fixed limit voltage value into a constant analogue output voltage for supplying the terminal.
10. The control device according to claim 1 , wherein the analogue difference signal is delivered, filtered by an analogue prefilter, to the analogue/digital converter.
11. The control device according to claim 1 , wherein the sequence of difference voltage values converted by the analogue/digital converter is downsampled by a first decimation filter.
12. The control device according to claim 11 , wherein the sequence of difference voltage values downsampled by the first decimation filter is filtered by a digital high-pass filter configured to filter out a sequence of information data.
13. The control device according to claim 1 , wherein the DC output voltage delivered by the first digital/analogue converter is filtered by an analogue low-pass filter.
14. The control device according to claim 13 , wherein an analogue adder is provided which is configured to add the DC output voltage filtered by the analogue low-pass filter to an AC signal voltage to form an analogue output voltage.
15. The control device according to claim 14 , wherein the output voltage is applied, amplified by an amplifier, to the subscriber line of the terminal.
16. The control device according to claim 15 , wherein the amplifier is integrated in an SLIC circuit.
17. The control device according to claim 16 , wherein the SLIC circuit has a current sensor configured to sense the line current flowing in the subscriber line of the terminal.
18. The control device according to claim 17 , wherein the SLIC circuit is configured to deliver the sensed line current, scaled, to the sensing circuit of the control device which is configured to generate an analogue input voltage proportional to the line current.
19. The control device according to claim 18 , wherein the sensing circuit is formed by a resistor.
20. The control device according to claim 9 , wherein the analogue low-pass filter has a switchable cut-off frequency.
21. The control device according to claim 1 , wherein the first digital/analogue converter and the second digital/analogue converter are formed by flash digital/analogue converters.
22. The control device according to claim 1 , wherein a compensation circuit configured to suppress a quantization error generated by the second digital/analogue converter during the conversion of a ramp-shaped signal is provided.
23. The control device according to claim 22 , wherein the compensation circuit is digitally configured.
24. The control device according to claim 23 , wherein the digital compensation circuit follows the first decimation filter in the circuit.
25. The control device according to claim 1 , wherein the control device is integrated in a CODEC circuit.
26. The control device according to claim 1 , wherein the terminal is a telephone.
27. A line card comprising:
a CODEC circuit comprising a control device configured to control a supply voltage according to claim 1 , and
an SLIC circuit configured to connect the terminal via a subscriber line.
28. A method for controlling a DC supply voltage for a terminal, comprising:
(a) sensing an analogue input voltage dependent on a line current;
(b) subtracting an analogue feedback voltage dependent on an adjustable nominal direct current value from the sensed input voltage for generating an analogue difference voltage;
(c) converting the generated analogue difference voltage into a digital difference voltage value;
(d) filtering a sequence of control error values out of the generated sequence of difference voltage values;
(e) generating a control value in dependence on the filtered-out sequence of control error values;
(f) converting the generated control value into the DC supply voltage; and
(g) converting the nominal direct-current value into the analogue feedback voltage.
29. A computer program for carrying out the method according to claim 28 .
30. A storage medium for storing a computer program according to claim 29 .