Patent Application
20150372846
The present invention relates to data communications, and more particularly to a dual band analog front end for high speed data transmissions.
ITU-T G.9701, commonly referred to as G.fast or the G.fast standard, defines a transceiver specification based on time division duplexing (TDD) for the transmission of the downstream and upstream signals in a bandwidth of approximately 106 MHz. The descriptions herein will refer to this system employing 106 MHz of bandwidth as the “first generation G.fast” system. In G.9701, a second profile for a 212 MHz bandwidth is currently planned for further study.
A first generation G.fast transceiver will use 106 MHz of channel bandwidth consisting of 2048 discrete multitone (DMT) tones (see profile 106a of the G.fast standard) and a 48 kHz symbol rate. In its second generation, a G.fast transceiver with 212 MHz of channel bandwidth is currently being planned. This system will use 4096 DMT tones and a 48 kHz symbol rate. According to the G.fast standard, the maximum bit loading can be as high as 12 bits/tone. In order to support this requirement, an analog to digital converter (ADC) with high resolution running at a very high sampling rate is needed.
A high resolution analog to digital converter (ADC) operating at a high sampling rate can consume a lot of power. Doubling the sampling rate from 212 MHz to 424 MHz can increase power consumption by far more than a factor of two if the effective number of bits (ENOB) coming out of the ADC needs to remain the same. Furthermore, the analog front end (AFE) is typically required to be backward compatible with no impact on power dissipation.
There is therefore a need for an AFE design that overcomes these obstacles, among others.
According to general aspects, embodiments of the invention provide an analog front end (AFE) capable of combining two independent 106 MHz G.fast baseband transmission channels into a single 212 MHz wide G.fast transmission channel. In these and other embodiments, an AFE according to the invention is also capable of interfacing to a single 212 MHz G.fast transmission channels as well as a single 106 MHz G.fast transmission channel.
In accordance with these and other aspects, an apparatus in a discrete multitone (DMT) communication system having a wide band of tones comprised of non-overlapping first and second sub-bands of tones according to embodiments of the invention includes transmit and receive pins coupled to a wire pair, a first transmit and receive channel, a second transmit and receive channel, and an analog front end (AFE) capable of selectively converting digital baseband signals from one or both of the first and second transmit and receive channels into an analog signal having a bandwidth corresponding to one or both of the first and second sub-bands and driven on the transmit pin.
These and other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures, wherein:
The present invention will now be described in detail with reference to the drawings, which are provided as illustrative examples of the invention so as to enable those skilled in the art to practice the invention. Notably, the figures and examples below are not meant to limit the scope of the present invention to a single embodiment, but other embodiments are possible by way of interchange of some or all of the described or illustrated elements. Moreover, where certain elements of the present invention can be partially or fully implemented using known components, only those portions of such known components that are necessary for an understanding of the present invention will be described, and detailed descriptions of other portions of such known components will be omitted so as not to obscure the invention. Embodiments described as being implemented in software should not be limited thereto, but can include embodiments implemented in hardware, or combinations of software and hardware, and vice-versa, as will be apparent to those skilled in the art, unless otherwise specified herein. In the present specification, an embodiment showing a singular component should not be considered limiting; rather, the invention is intended to encompass other embodiments including a plurality of the same component, and vice-versa, unless explicitly stated otherwise herein. Moreover, applicants do not intend for any term in the specification or claims to be ascribed an uncommon or special meaning unless explicitly set forth as such. Further, the present invention encompasses present and future known equivalents to the known components referred to herein by way of illustration.
According to certain general aspects, embodiments of the invention provide an Analog Front End (AFE) for the second and higher generations of G.fast that addresses the problems described above, among other things.
In embodiments of the invention, a channel with large bandwidth is broken down into two or more non-overlapping sub bands, for example a lower sub band and an upper sub band. Each of these sub bands can be mapped to an independent base band channels via appropriate up/down conversion. Each of these base band channels can be then processed via separate circuits with ADCs operating at lower sampling rates.
According to one aspect, embodiments of the invention implement a general approach of taking two independent first generation G.fast transceivers that use 2048 tones (106 MHz bandwidth) and combining them in a certain way to create a second generation G.fast transceiver that uses 4096 tones (212 MHz Bandwidth). The G.fast transceivers according to the invention can be included in CO transceivers 120, CPE transceivers 110 or both of CO transceivers 120 and CPE transceivers 110.
More particularly, the present inventors further recognize that a channel with 212 MHz bandwidth can be broken down into two non-overlapping 106 MHz sub bands. For example, as shown in
According to embodiments of the invention, furthermore, the present inventors recognize that two first generation G.fast transceivers can be used in combination to transmit and receive data over a bonded channel 206 using up to the 4096 tones in both of sub-bands 202 and 204, thus providing an aggregate rate well over 1 Gbps. In fact, over very short loops the aggregate data rate could approach 2 Gbps.
It should be noted that the principles of the invention can be extended to future generations of G.fast (e.g. up to 318 MHz) or other high bandwidth systems. In an example generation of G.fast operating with bandwidths up to 318 MHz, alternative embodiments of the invention can use three 106 MHz sub-bands and three first generation G.fast transceivers.
A block diagram illustrating an example DPU 100 for implementing aspects of the present invention is shown in
As further shown in the example of
It should be noted that a dual band AFE according to embodiments of the invention is not limited to being included in a DPU having the additional components of channels 310 such as that shown in the example implementation of
In general operation of the example implementation shown in
Additional operational and implementation aspects of central controller 312, G.fast transceivers 120 and digital bonding module 302 are described in co-pending U.S. application Ser. No. ______ (14IK11), which is incorporated by reference herein in its entirety.
One example implementation of AFE 304 according to embodiments of the invention is illustrated in
Referring to
For example, in the event the AFE 304 is to be used to interface with a single 106 MHz G.fast transceiver 120, the transceiver input/output will be connected to CH0_RX/TX. The digital mux A is switched by central controller 312 to select the channel CH0_TX. The transmit digital signal from the CH0_TX is converted to analog by DAC0 operating at a 212 MHz rate according to F1, filtered by the TX LPF and coupled to through ATX to line 104. The path through the HPF is disabled by central controller 312 in this case. The signal on the line 104 has a maximum bandwidth of 106 MHz in sub-band 202 matching the digital input at CH0_TX. In the receive direction, the analog signal from the line 104 on ARX is amplified by the LNA, filtered by the LPF0 and converted to digital by ADC0 operating at the 212 MHz rate according to F1. Once again, the digital signal at CH0_RX has the same maximum bandwidth (106 MHz) as the analog signal on ARX.
In the event the AFE 304 is to be used to interface with two 106 MHz G.fast DSP transceivers 120 which are to be merged into one 212 MHz analog signal on the line 104 (e.g. a bonded signal such as that described in more detail in co-pending application Ser. No. ______ (14IK11)), the inputs/outputs of the two transceivers are connected to CH0_RX/TX and CH1_RX/TX. Mux A is switched by central controller 312 to select CH0_TX, mux B is configured by central controller 312 to select CH1_TX and mux C is configured by central controller 312 to select the output of ADC1. The digital transmit signal on CH0_TX is coupled to the line 104 through DAC0 operating at a 212 MHz rate according to F1 and TX LPF. It will occupy a bandwidth from 0-106 MZz corresponding to sub-band 202. The second channel CH1_TX, is converted to digital by DAC1 operating at a 212 MHz rate according to F1, frequency translated by a mixer operating at a 106 MHz according to F2 and filter by the HPF such that the signal bandwidth sits from 106 MHz to 212 MHz corresponding to sub-band 204. These are combined and coupled to the line 104 through pin ATX. The resulting signal will have a combined bandwidth 206 from 0 to 212 MHz. In the receive direction, the 212 MHz bandwidth signal on line 104 from the ARX pin is amplified by the LNA, it is split into high frequency and low frequency pieces by the LPF0 and HPF1. The high frequency piece is mixed down to baseband using a mixer operating at a 106 MHz rate according to F2, and filtered by LPF1. Both ADC1 and ADC0 operating at a 212 MHz rate according to F1 convert the analog signals which both occupy 0 to 106 MHz bandwidths. These digital signals are sent on CH1_RX and CH0_RX to the two first generation G.fast transceivers.
In the event the AFE 304 is to be used to interface with one 212 MHz G.fast transceiver 120 (in a different embodiment of channel 310), the transceiver input/output is connected to CH1_RX/TX. Mux A is configured by central controller 312 to select the output of the “LPF+DEC” block, mux B is configured by central controller 312 to select the output of the “Dwn Mixer” block and mux C is configured by central controller 312 to select the output of the “+” block. The CH1_TX digital transmit signal is digitally split into its upper and lower bands 202 and 204 by the LPF+DEC and HPF+DEC blocks. The high frequency section is frequency translated to lower frequency by the Dwn Mixer. The two 106 MHz bandwidth signals are then converted by DAC0 and DAC1 operating at 212 MHz according to F1 to analog. The output of DAC1, which represents the high frequency piece, is translated to the higher frequency and combined with the lower frequency piece and sent to the line 104 through ATX. In the receive direction, the 212 Mhz signal from the line 104 is split into high and low frequency pieces in the analog domain as described earlier. In the digital domain, the signals are re-combined maintaining the spectral content and sent as one 212 Mhz band signal on CH1_RX.
It should be noted that while
Embodiments of the invention achieve lower power dissipation in the ADC since they run at lower frequencies and do not require calibration for path mismatch which would be the case for time interleaved converters.
Moreover, each ADC's dynamic range is more efficiently utilized by the Automatic Gain Control (AGC) as the ADCs only see “in-band” signals. The implementation also supports backward compatibility with 106 MHz G.fast standard while supporting 212 MHz G.fast standard. And finally, the implementation can be used for “bonding” two G.fast 106 MHz channels to increase data rate.
Although the present invention has been particularly described with reference to the preferred embodiments thereof, it should be readily apparent to those of ordinary skill in the art that changes and modifications in the form and details may be made without departing from the spirit and scope of the invention. It is intended that the appended claims encompass such changes and modifications.
The present application claims priority to U.S. Prov. Appln. No. 62/015,149 filed Jun. 20, 2014, the contents of which are incorporated by reference herein in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62015149 | Jun 2014 | US |
