Analog front end multiplexer for CMTS receiver

• US 20040248530A1
• Filed: 07/08/2002
• Published: 12/09/2004
• Est. Priority Date: 07/08/2002
• Status: Abandoned Application

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Inventors: Azenkot, Yehuda, Rakib, Selim Shlomo
• Application Number:
  US10/191,164
• Publication Number:
  US 20040248530A1
• Time in Patent Office: Days
• US Class Current: 455/127.4
• CPC Class Codes: H04L 27/0002 analog front ends; means for connecting modulators, demodulators or transceivers to a transmission line duplex arrangements H04L5/143
• CPC Class Codes: H04L 5/06 the signals being represented by different frequencies combined with time-division multiplexing H04L5/26

Abstract

An analog multiplexer front end circuit for a Cable Modem Termination System receiver to utilize one or a handful of CMTS receiver chips to receive and recover data from a larger number of input cables coupled to the analog multiplexer. A control circuit for the multiplexer uses MAP data and upstream mini-slot counts for each of the input cables to determine when a burst is about to arrive on an cable. In some embodiments, there is only one RF channel circuit coupled to the output of the multiplexer, so the multiplexer is controlled to couple the input cable upon which the burst is expected to the single RF channel. In other embodiments, there are multiple RF channels so the multiplexer is controlled to connect each input cable on which a burst is expected to an available W channel. In some embodiments, the sample data generated by each RF channel is buffered and an arbiter picks one burst at a time for application to the input of a CMTS receiver. In other embodiments, no buffers or arbiter are used, and each RF channel has its own dedicated CMTS receiver.

Claims

1. An apparatus comprising:

an analog multiplexer having a plurality of analog radio frequency inputs and a plurality of analog radio frequency outputs, and having a control input for receiving control signals;

a plurality of radio frequency channel circuits (hereafter RF channels), each having an input coupled to one of said radio frequency outputs of said analog multiplexer; and

control means coupled to supply said control signals to said analog multiplexer to control the timing and selection of coupling each of one or more selected radio frequency outputs to one or more selected radio frequency inputs through said analog multiplexer.

2. The apparatus of claim 1 wherein each radio frequency control channel comprises:

mixer circuitry to mix the frequency of a selected logical channel in the input signal received from said analog multiplexer down to an analog baseband signal;

analog-to-digital conversion circuitry to sample said analog baseband circuitry; and

a buffer to store sample data output by said analog-to-digital conversion circuitry.

3. The apparatus of claim 2 further comprising a filter to filter out at least some frequencies outside the bandwidth of said selected logical channel.

4. The apparatus of claim 1 wherein said control means comprises:

a memory;

an interface circuit for communicating with a media access control process;

a programmed microprocessor coupled to said memory and said interface circuit and having an output coupled to said control input of said analog multiplexer.

5. The apparatus of claim 4 wherein said microprocessor is programmed to:

receive MAP data and the current mini-slot count for each radio frequency input of said multiplexer from a Media Access Control process (hereafter MAC process) and store said MAP data and said current mini-slot count in said memory;

compare the current mini-slot count for each radio frequency input of said multiplexer to MAP data for said input to determine when to expect a burst on said input;

maintaining a list of available radio frequency channel signals using said MAP data and data regarding which assignments have been made to which RF channels to process bursts;

when a burst is to be received, selecting an available RF channel using said list of available radio frequency channels, and generating appropriate control signals to control said multiplexer to connect a radio frequency input on which said burst will arrive to said radio frequency output coupled to said available RF channel.

6. The apparatus of claim 5 wherein said microprocessor is programmed to send data regarding which RF channel has been assigned to process each burst to said MAC process.

7. The apparatus of claim 5 wherein each said RF channel circuit includes an input coupled to receive data from said MAC process which controls the frequency of a local oscillator signal which said RF channel circuit mixes with a radio frequency signal modulated with the data of a burst to be received to mix said burst'"'"'s radio frequency signal down to baseband.

8. The apparatus of claim 5 wherein said microprocessor is programmed to generate an appropriate control signal for a local oscillator in said RF channel circuit assigned to process each burst and to transmit said control signal to said local oscillator to cause said local oscillator to generate a local oscillator signal having a frequency which when mixed with the frequency of the radio frequency signal modulated with said burst to be received causes said radio frequency signal modulated with said burst to be received to be mixed down to baseband.

9. The apparatus of claim 1 wherein said control means comprises:

a memory;

an interface circuit for communicating with a media access control process;

a state machine coupled to said memory and said interface circuit and coupled directly or indirectly through a decoder to said control input of said analog multiplexer.

10. The apparatus of claim 1 further comprising:

a buffer in each said RF channel circuit coupled to receive and store sample data output by an analog-to-digital conversion circuit in said RF channel circuit;

any arbiter coupled to said buffers and having an output, for selecting burst data stored in said buffers according to any arbitration scheme and presenting said burst data at said output;

11. The apparatus of claim 10 further comprising any Cable Modem Termination System receiver having a burst data input coupled to said output of said arbiter.

12. The apparatus of claim 1 further comprising a plurality of Cable Modem Termination Systems receivers, each being of any type and each having a burst data input coupled to an output of an RF channel.

13. An apparatus comprising:

an analog multiplexer having a plurality of analog radio frequency inputs and a plurality of analog radio frequency outputs, and having a control input for receiving control signals;

a plurality of radio frequency channel circuits (hereafter RF channels), each having an input coupled to one of said radio frequency outputs of said analog multiplexer and each comprising at least a mixer to mix a selected logical channel down to baseband and an analog-to-digital converter to sample the baseband signals and a buffer to store samples output by said analog-to-digital converter; and

control means coupled to supply said control signals to said analog multiplexer to control the timing and selection of coupling each of one or more selected radio frequency outputs to one or more selected radio frequency inputs through said analog multiplexer;

any arbiter structured and coupled to read data from each said buffer and output data for one burst at a time according to any arbitration scheme; and

any Cable Modem Termination System receiver coupled to receive the selected burst data from said arbiter.

14. An apparatus comprising:

an analog multiplexer having a plurality of analog radio frequency inputs and a plurality of analog radio frequency outputs, and having a control input for receiving control signals;

a plurality of radio frequency channel circuits (hereafter RF channels), each having an input coupled to one of said radio frequency outputs of said analog multiplexer and each comprising at least a mixer to mix a selected logical channel down to baseband and an analog-to-digital converter to sample the baseband signals; and

control means coupled to supply said control signals to said analog multiplexer to control the timing and selection of coupling each of one or more selected radio frequency outputs to one or more selected radio frequency inputs through said analog multiplexer;

a plurality of any type of Cable Modem Termination System receivers, each coupled to receive output data from an RF channel.

15. The apparatus of claim 14 wherein each RF channel circuit has an input to receive control data from a Media Access Control process which defines the center frequency of the logical channel upon which data of a burst to be processed by said RF channel circuit is modulated, and wherein said control circuit is structured to assign each burst to an available RF channel circuit and to maintain data regarding the availability of each RF channel circuit and to inform said Media Access Control process each time an assignment of an RF channel circuit is made.

16. The apparatus of claim 14 wherein each RF channel circuit includes a digital filter and has an input to receive control data from a Media Access Control process which defines the center frequency and symbol rate of the logical channel upon which data of a burst to be processed by said RF channel circuit is modulated, and wherein said control circuit is structured to assign each burst to an available RF channel circuit and to maintain data regarding the availability of each RF channel circuit and to inform said Media Access Control process each time an assignment of an RF channel circuit is made, and wherein said RF channel circuit is structured to use said control data defining the center frequency of said logical channel to control a local oscillator to generate a signal which when mixed with said logical channel signal mixes said logical channel down to baseband, and is further structured to use said control data defining said symbol rate to set filter coefficients for said digital filter which filters out at least some noise outside the bandwidth of said logical channel.

17. The apparatus of claim 14 wherein each RF channel circuit has an input to receive control data from said control circuit which defines the center frequency of the logical channel upon which data of a burst to be processed by said RF channel circuit is modulated.

18. The apparatus of claim 14 wherein each RF channel circuit has a digital filter and has an input to receive control data from said control circuit which defines the center frequency and symbol rate of the logical channel upon which data of a burst to be processed by said RF channel circuit is modulated, and wherein said RF channel circuit is structured to use said control data defining said center frequency to control the frequency of a local oscillator signal which is mixed with said logical channel signal to mix it down to baseband, and is further structured to use said control data defining said symbol rate to set coefficients of said digital filter to filter out at least some signals outside the bandwidth of said logical channel.

19. An apparatus comprising:

an analog multiplexer having a plurality of analog radio frequency inputs and a single analog radio frequency output, and having a control input for receiving control signals;

a single radio frequency channel circuit (hereafter RF channels), having an input coupled to one of said radio frequency output of said analog multiplexer, and comprising at least a mixer to mix a selected logical channel down to baseband and an analog-to-digital converter to sample the baseband signals; and

control means coupled to supply said control signals to said analog multiplexer to control the timing and selection of coupling said radio frequency output to a selected radio frequency input through said analog multiplexer to receive a burst modulated onto the radio frequency signals of a logical channel;

a Cable Modem Termination System receiver coupled to receive output data from said RF channel.

20. The apparatus of claim 19 wherein said RF channel includes a tunable filter to filter out most noise outside the passband of the selected logical channel.

21. The apparatus of claim 20 wherein said RF channel includes an input for receiving control data which defines the center frequency of the selected logical channel and which defines the symbol rate and bandwidth of said selected logical channel, and wherein said RF channel circuitry is structured to use said control data to define the frequency generated by a local oscillator to mix the selected logical channel down to baseband and to use said control data defining the bandwidth to tune said filter to filter out most of the noise outside the bandwith of said selected logical channel.

22. A process comprising:

receiving and storing MAP data for each of a plurality of input cables each cable carrying bursts of upstream data transmitted on RF signals of a logical channel during mini-slots assigned by a Media Access Control process, said MAP data defining the beginning and ending mini-slot of each burst on each cable;

determining the current upstream mini-slot count for each of said input cables;

comparing the current mini-slot count for each cable to the MAP data for said input cable, and generating switching control data to control switching of an analog multiplexer having a plurality of inputs coupled to said input cables to connect an input cable upon which a burst will be arriving to an available RF channel circuit for processing;

mixing the RF signals of the selected burst down to baseband and taking digital samples of the baseband signal.

23. A process comprising:

receiving and storing MAP data for each of a plurality of input cables each cable carrying bursts of upstream data transmitted on RF signals of a logical channel during mini-slots assigned by a Media Access Control process, said MAP data defining the beginning and ending mini-slot of each burst on each cable;

determining the current upstream mini-slot count for each of said input cables;

comparing the current mini-slot count for each cable to the MAP data for said input cable, and generating switching control data to control switching of an analog multiplexer having a plurality of inputs coupled to said input cables to connect an input cable upon which a burst will be arriving to an available RF channel circuit for processing after determining which of a plurality of RF channel circuits is available to process a burst;

in each RF channel circuit which has been assigned to process a burst, mixing the RF signals of the selected burst down to baseband and taking digital samples of the baseband signal;

in each RF channel circuit, storing said sample data in a buffer;

arbitrating between RF channels to read sample data out of the buffers of said RF channels on the basis of any arbitration scheme and providing the selected sample data at an output; and

receiving the selected sample data and recovering said burst data therefrom.

24. A process comprising:

receiving and storing MAP data for each of a plurality of input cables each cable carrying bursts of upstream data transmitted on RF signals of a logical channel during mini-slots assigned by a Media Access Control process, said MAP data defining the beginning and ending mini-slot of each burst on each cable;

determining the current upstream mini-slot count for each of said input cables;

comparing the current mini-slot count for each cable to the MAP data for said input cable, and generating switching control data to control switching of an analog multiplexer having a plurality of inputs coupled to said input cables to connect an input cable upon which a burst will be arriving to an available RF channel circuit for processing after determining which of a plurality of RF channel circuits is available to process a burst;

in each RF channel circuit which has been assigned to process a burst, mixing the RF signals of the selected burst down to baseband and taking digital samples of the baseband signal;

receiving the sample data from each RF channel in a Cable Modem Termination System receiver dedicated to said RF channel, and recovering said burst data therefrom.