High output power digital-to-analog converter system
The present disclosure discloses a digital-to-analog converter (DAC) design which is suitable for providing a high output power high-speed DAC, e.g., in radio frequency applications. The DAC design utilizes a parallel DAC structure, e.g., having 8 parallel DACs and an aggregate current output, to provide a high and programmable current output (in some implementations, up to 512 mA or more). The parallel DAC structure alleviates the design problems which exist in trying to output a high amount of current using a single DAC. The DAC design further utilizes a hybrid structure which integrates the signal chain for a more reliable system. In some embodiments, the hybrid structure uses a CMOS process for the current sources and switches and a GaAs cascode stage for combining the outputs to optimally leverage the advantages of both technologies. The result is a highly efficient DAC (with peak output power programmable up to 29 dBm or more).
1. A digital to analog converter (DAC), the DAC comprising:
M parallel DAC cores, wherein:
M is an integer greater or equal to 4;
each DAC core converts a digital input signal to an analog output signal; and
the same input digital word is provided as the digital input signal to the plurality of parallel DAC cores; and
a cascode stage directly connected to the outputs of the M parallel DAC cores for combining the outputs of the M parallel DAC cores to provide an aggregate analog output.
2. The DAC of claim 1 , wherein M is greater or equal to 8.
3. The DAC of claim 1 , wherein:
the M parallel DAC cores are built using any one or more of the following: complementary metal-oxide-semiconductor (CMOS) technology, bipolar-complementary metal-oxide-semiconductor (BiCMOS), and silicon-on-insulator (SOI); and
the cascode stage comprises Gallium Arsenide (GaAs) cascodes and/or Gallium Nitride (GaN) cascodes.
4. The DAC of claim 1 , wherein:
the cascode stage comprises a M cascodes each connected to a corresponding parallel DAC cores directly through a network of traces.
5. The DAC of claim 1 , wherein:
the M number of parallel DAC cores comprises M differential output pairs or 2M differential outputs;
the M cascodes comprises M differential input pairs or 2M differential inputs; and
the M differential output pairs or 2M differential outputs of parallel DAC cores are connected directly to the M differential input pairs or 2M differential outputs of the cascodes respectively through the network of traces.
6. The DAC of claim 2 , wherein:
the 8 parallel DAC cores are grouped into pairs of 2 parallel DACs as 4 dual-DACs in the hardware layout of the DAC.
7. The DAC of claim 6 , wherein:
each of 8 parallel DAC comprises (1) an array of current sources, and (2) a bank of switches and switch drivers; and
(1) the array of current sources and (2) the bank of switches and the switch drivers are arranged in the outer area of the 4 dual-DACs in the hardware layout of the DAC.
8. The DAC of claim 6 , wherein:
each dual-DAC comprises a DAC decoder and a high speed multiplexer; and
the DAC decoder and the high speed multiplexer are shared between the two parallel DAC of each dual-DAC.
9. The DAC of claim 6 , wherein:
the hardware layout of every adjacent dual-DAC is flipped to compensate for timing skew and/or the gradient.
10. The DAC of claim 6 , further comprising:
the hardware layout of each dual-DAC has an array of N cells for receiving and processing N bits of a digital word arranged in a particular order of the N bits; and
the particular order of the N bits that the array of N cells processes alternates for the dual-DACs between a regular order and a reversed order.
11. The DAC of claim 6 , wherein:
the hardware layout of each dual-DAC has an array of X+Y cells for receiving and processing X least significant bits and Y most significant bits;
the array of X+Y cells comprises a top part, a middle part, and a bottom part arranged in the hardware layout;
the cells for receiving and processing the least significant bits are distributed in the top part and the bottom part; and
the cells for receiving and processing the most significant bits of the digital input word are distributed in the middle part.
12. The DAC of claim 6 , wherein:
the hardware layout of each dual-DAC has an array of N cells for receiving and processing N bits of a digital input word;
for every other dual-DAC, the array of N cells receives and processes the N bits arranged in a first order of the N bits;
for the other dual-DACs, the array of N cells receives and processes the N bits arranged in a second order of the N bits; and
wherein the second order complements the first order.
13. The DAC of claim 12 , wherein:
the first order of the N bits are defined by at least some of the bits in even positions arranged in an ascending order according to the bit position for a contiguous portion of the array of N cells and at least some of the bits in odd positions arranged in a descending order according to the bit position for the contiguous portion of the array of N cells.
14. The DAC of claim 12 , wherein:
the first order of the N bits are defined by at least some of the bits in even positions in ascending order are arranged as every other bit in the first order for at least a contiguous portion of the array of N cells, along with at least some of the bits in odd positions in descending order as the other bits in the first order for the contiguous portion of the array of N cells.
15. The DAC of claim 1 , wherein:
the DAC generates an analog output signal having a current between 256 milliamps to 512 milliamps.
16. The DAC of claim 1 , wherein:
the DAC generates an analog output signal having a current between 512 milliamps to 3 amps.
17. A digital-to-analog converter (DAC) system for converting a digital input signal to an analog output signal, the DAC system comprising:
a DAC stage comprising M parallel DAC cores, wherein M is equal to or greater than 4;
a cascode stage comprising M parallel cascodes connected to the output of the eight parallel DAC cores, the cascode stage configured to amplify and combine the outputs of the M parallel DAC cores, wherein the outputs of the DAC cores in the DAC stage and inputs of the cascodes in cascode stage are directly connected through a network of traces; and
a digital pre-distortion processor for (1) providing an inverse of the non-linearity as input to the DAC stage and/or the cascode stage to compensate non-ideal errors of the DAC stage and/or the cascode stage and/or (2) restore the ideal waveforms to compensate the non-ideal errors present in the DAC stage and/or the cascode stage.
18. The DAC system of claim 17 , wherein the M is greater than or equal to 8.
19. The DAC system of claim 17 , wherein the digital pre-distortion processor is an open-loop digital pre-distortion processor.
20. An apparatus for providing a finite impulse response filter (FIR), the apparatus comprising:
M parallel DAC cores, wherein M is an integer greater or equal to 4 and each DAC core converts a digital input signal to an analog output signal;
a cascode stage directly connected to the outputs of the M parallel DAC cores for combining the outputs of the M parallel DAC cores to provide an aggregate analog output;
a digital signal processor configured to distribute different input codes to the M parallel DAC cores to provide a finite impulse response (FIR) filter using the M parallel DACs;
a cascode stage comprising a network of M cascodes connected to the M parallel DAC cores, the cascode stage configured to perform a summation for the FIR filter;
wherein:
each of the M parallel DACs uses different input codes to implement delay for the FIR filter;
each of the M parallel DACs comprises an array of current sources for performing linear multiplication for the FIR filter; and
the output current of each of the M parallel DACs are programmable to correspond to multiplier coefficients for the FIR filter.