Time-slot interchange circuit
View Patent ↗A circuit and method are presented for signal processing and routing of digital voice telephony signals, using a specialized high-density integrated circuit voice processor. The voice processor performs several essential functions required for telephony processing, including echo cancellation, protocol conversion, and dynamic range compression/expansion. These functions are traditionally performed by multiple circuits or modules. By combining these capabilities in a single device, power and circuit board area requirements are reduced. The embodiment of the circuit and method disclosed herein include novel implementations of a time-slot interchange circuit and a telephony signaling circuit. Both of these circuits are designed to minimize demands on the signal processing engines incorporated within the voice processor, and account for very little of the on-chip circuitry.
1. A time-slot interchange circuit comprising:
a plurality of input ports receiving a plurality of input data streams, each of said input data streams comprising a plurality of bits;
a plurality of shift registers, (i) each one of said shift registers having m stages and m is at least two, (ii) each one of said shift registers corresponds to one of said input data streams and (iii) said bits within each one of said input data streams received from said input ports are (a) synchronously clocked through said corresponding shift registers in a first mode and (b) asynchronously clocked in a second mode; and
a plurality of multiplexers routing said bits from said shift registers to a plurality of output ports, each of said multiplexers temporally selecting said bits from at least two of said shift registers into a respective one of said output data streams.
2. The time-slot interchange circuit as recited in claim 1 , wherein (i) said input data streams comprise time-division multiplexed (TDM) data streams and (ii) at least one of said TDM data streams conveys TDM voice data occupying a plurality of time-slots in a frame of data.
3. The time-slot interchange circuit as recited in claim 1 , wherein in said first mode (i) said multiplexers share a common clock and (ii) said output data streams share frame-sync timing.
4. The time-slot interchange circuit as recited in claim 1 , wherein m=2.
5. The time-slot interchange circuit as recited in claim 1 , wherein each of said input data streams is transferred directly from a respective output node of said input ports to a respective input node of said shift registers.
6. The time-slot interchange circuit as recited in claim 1 , wherein each of said input data streams is transferred directly from a respective output node of said shift registers to a corresponding input node of all of said multiplexers.
7. The time-slot interchange circuit as recited in claim 1 , wherein each of said output data streams is transferred directly from a respective output node of said multiplexers to a respective input node of said output ports.
8. The time-slot interchange circuit as recited in claim 1 , wherein a particular one of said input data streams is clocked into a respective one of said shift registers sequentially, one bit at a time.
9. The time-slot interchange circuit as recited in claim 1 , wherein said synchronous clocking of said shift registers in said first mode is controlled through a single one of said input ports.
10. A method for redistributing a plurality of bits arriving in a plurality of input data streams to a plurality of output data streams, comprising the steps of:
(A) receiving said input data streams at a plurality of input ports;
(B) synchronously clocking said bits in each one of said input data streams received from said input ports through a corresponding one of a plurality of shift registers in a first mode, each of said shift registers having m stages and m is at least two;
(C) asynchronously clocking said bits through said shift registers in a second mode; and
(D) routing said bits from said shift registers through a plurality of multiplexers to a plurality of output ports, each one of said multiplexers temporally selecting said bits from at least two of said shift registers into a respective one of said output data streams.
11. The method as recited in claim 10 , wherein (i) said input data streams comprises a time-division multiplexed (TDM) data streams and (ii) at least one of said TDM data streams conveys TDM voice data occupying a plurality of time slots within a frame of data.
12. The method as recited in claim 10 , wherein in said first mode (i) said multiplexers share a common clock and (ii) said output data streams share frame-sync timing.
13. The method as recited in claim 10 , wherein m=2.
14. The method as recited in claim 10 , further comprising the step of:
transferring each of said input data streams directly from a respective output node of said input ports to a respective input node of said shift registers.
15. The method as recited in claim 10 , further comprising the step of:
transferring each of said input data streams directly from a respective output node of said shift registers to a corresponding input node of all of said multiplexers.
16. The method as recited in claim 10 , further comprising the step of:
transferring each of said output data streams directly from a respective output node of said multiplexers to a respective input node of said output ports.
17. The method as recited in claim 10 , further comprising the step of:
clocking a particular one of said input data streams into a respective one of said shift registers sequentially, one bit at a time.
18. The method as recited in claim 10 , further comprising the step of:
controlling said synchronous clocking of said shift registers in said first mode through a single one of said input ports.