High-speed flash analog to digital converter

#A computer network is any set of computers coupled to each other with the ability to exchange data. The interconnections between computers enable communication with a variety of different kinds of media, including twisted-pair wires, coaxial cables, fiber optic cables, power lines, Ethernet and various wireless technologies. Faster interconnections generally improve network performance by reducing latency and increasing communication bandwidth. Higher bandwidths enable desirable services such as social media, video conferencing, multi-media transfers, etc. Further, an increased capacity for uploads and downloads can create a huge boost in productivity for any individual or business entity—the speedier the connections, the better the network's utility to its users.

#The interconnections (such as fiber optic cables, twisted pair wires, coaxial cables, etc.) carry analog electrical or optical signals between transceivers. The signal may be, for example, an electrical voltage, an electrical current, an optical power level, a wavelength, a frequency, or a phase value. The receiver receives the signal, converts that analog electrical or optical signal into digital format, and extracts the transmitted data stream for use by the receiving node. The analog-to-digital conversion often employs a flash analog to digital converter.

#A flash analog to digital converter is a type of fast converter that uses a linear voltage ladder and a comparator at each “step” in the ladder. The comparators operate in parallel to compare the input voltage to each of the reference voltages. Often these ladders are constructed of a series of resistors, but capacitive voltage division is also possible. Though flash converters are extremely fast, they typically require a large number of comparators relative to other analog to digital converter implementations, especially as the precision increases. A flash converter requires 2n-1 comparators for an n-bit conversion. The output of these comparators is generally fed into a digital encoder which converts the inputs into a binary value.

#A better understanding of the various disclosed system and method embodiments can be obtained when the following detailed description is considered in conjunction with the drawings, in which:

#FIG. 1 shows an illustrative computer network;

#FIG. 2 shows an illustrative point-to-point communication link;

#Accordingly, disclosed herein are some embodiments for a high-speed analog to digital converter. In at least one embodiment, a flash analog-to-digital converter includes a linear voltage ladder and a series of comparators, each of which is coupled to at least one operational amplifier by a sampling switch. Each of the sampling switches samples the comparator output, using the parasitic capacitance of the operational amplifier to hold the voltage. The sampling switches may be single transistors. Some embodiments further include, for each comparator, multiple operational amplifiers each of which drives a binary latch via a gating switch. The gating switches operate in sequence to distribute sequential samples to different latches. At least some embodiments of the flash converter further include an automatic gain control (AGC) that has both differential input terminals and differential output terminals. In such embodiments the comparators compare the differential output of the AGC to a differential reference voltage, and may further provide the result as a differential signal. The operational amplifiers may be coupled to a set of latches that hold a the output signal from said operational amplifiers as a digital value.

#The flash analog to digital converter may be part of a high-speed digital communication receiver system that includes a transducer and an analog filter. The flash analog to digital converter may provide interleaved sampling so as to provide a demodulator with digitized values for both in-phase and quadrature components of a receive signal.

#The disclosed embodiments are best understood in terms of the environment in which they may be expected to operate. Accordingly, FIG. 1 shows an illustrative computer network 100 including computer systems 104A-C coupled to a routing network 106. The routing network 106 may be or include, for example, the Internet, a wide area network, a local area network, wireless networks, and/or portions of the telephone network. In FIG. 1, the routing network 106 includes a network of equipment items 108, such as switches, routers, and the like. The equipment items 108 are connected to one another, and to the computer systems 104A-C, via point-to-point communication links 110 that transport data between the various network components. Today, more and more communication links are being developed with an emphasis on speed. IEEE Std 802.3ba-2010 supports sending Ethernet frames at 40 and 100 gigabits per second, with individual channel signaling rates as high as 25 Gb/s. Previously, the fastest published Ethernet standard provided for a data rate of 10 Gb/s.