Systems and methods for delta-sigma digitization
A baseband processing unit includes a baseband processor configured to receive a plurality of component carriers of a radio access technology wireless service, and a delta-sigma digitization interface configured to digitize at least one carrier signal of the plurality of component carriers into a digitized bit stream, for transport over a transport medium, by (i) oversampling the at least one carrier signal, (ii) quantizing the oversampled carrier signal into the digitized bit stream using two or fewer quantization bits.
1. A hub transmitter for a digital fiber link, comprising:
a delta-sigma analog-to-digital converter (ADC) configured to (i) obtain a digitized sequence of an input analog signal within a target bandwidth of the digital optical link, (ii) apply a noise transfer function (NTF) to the digitized sequence to generate a digitized output signal that is substantially separated, in the frequency domain, from quantization noise of the digitized sequence; and
an output interface configured to transmit the digitized output signal to a remote receiving unit in operable communication with the digital optical link,
wherein the NTF of the ADC corresponds to a filter of the remote receiving unit, such that the remote receiving unit is enabled to, upon receipt of the transmitted digitized output signal, retrieve from the digitized output signal a second analog signal that is substantially similar to the input analog signal within the target bandwidth.
2. The transmitter of claim 1 , wherein the filter of the remote receiving unit is a passive filter.
3. The transmitter of claim 2 , wherein the NTF includes a frequency response corresponding to a high pass filter configured for first frequency range greater than a second frequency range corresponding to the passive filter of the remote receiving unit.
4. The transmitter of claim 1 , wherein the delta-sigma ADC comprises a cascade-of-resonators feedback (CRFB) structure.
5. The transmitter of claim 4 , wherein the CRFB structure includes a digital-to-analog converter (DAC).
6. The transmitter of claim 5 , wherein the CRFB structure includes (i) an input portion configured to receive the digitized sequence of the input analog signal, and (ii) an output portion configured to output the digitized output signal.
7. The transmitter of claim 6 , wherein the DAC is disposed along a feedback portion of the CRFB structure between the input portion and the output portion.
8. The transmitter of claim 5 , wherein an order number of the CRFB structure corresponds to a number zeroes and poles of the NTF in an in-phase/quadrature (I/Q) plane.
9. The transmitter of claim 8 , wherein the CRFB structure comprises a fourth-order ADC and wherein the NTF includes four zeroes and four poles in the I/Q plane.
10. The transmitter of claim 9 , wherein the NTF includes two conjugate pairs of zeroes and poles.
11. The transmitter of claim 9 , wherein the delta-sigma ADC further includes a sampling unit configured to digitize the input analog signal into the digitized sequence at a sampling rate of at least 32 GSa/s.
12. The transmitter of claim 11 , wherein the delta-sigma ADC is further configured to generate the digitized output signal at 32 Gbaud or greater.
13. The transmitter of claim 11 , wherein the CRFB structure comprises a quantizer disposed proximate the output portion.
14. The transmitter of claim 13 , wherein the feedback portion of the CRFB structure operably connects the DAC with a digitized waveform output from the quantizer.
15. The transmitter of claim 14 , wherein the quantizer is a one-bit quantizer, and wherein the digitized waveform is an on-off keying (OOK) signal.
16. The transmitter of claim 14 , wherein the quantizer is a two-bit quantizer, and wherein the digitized waveform is a four-level pulse amplitude modulation (PAM4) signal.
17. The transmitter of claim 1 , wherein the receiving unit includes a modem configured to obtain the second analog signal from the filter.
18. The transmitter of claim 1 , wherein the digitized sequence of the input analog signal includes one or more communication channels transmitted according to the data over cable service interface specification (DOCSIS).
19. The transmitter of claim 18 , wherein the second analog signal includes one or more retrieved DOCSIS communication channels corresponding to the one or more transmitted DOCSIS communication channels from the first analog signal.
20. The transmitter of claim 19 , further configured to assign a modulation format to each DOCSIS carrier of the one or more transmitted DOCSIS communication channels according to a carrier-to-noise ratio of the particular DOCSIS communication channel.