Various aspects of the subject technology relate to systems, methods, and machine-readable media for DDR reference voltage training. The method includes receiving a data stream, the data stream including pulses generated from a reference voltage in relation to a voltage input logic low and a voltage input logic high of an input stream. The method also includes receiving a clock signal, the clock signal including an in-phase signal and a quadrature-phase signal, the in-phase signal orthogonal to the quadrature-phase signal. The method also includes utilizing the in-phase signal and the quadrature-phase signal of the clock signal in relation to the data stream to obtain a stream of in-phase samples and a stream of quadrature-phase samples. The method also includes adjusting the reference voltage based on a relationship of the stream of in-phase samples to the stream of quadrature-phase samples.

Apparatus and methods for clock duty cycle correction and deskew are provided. In certain embodiments, a clock distribution circuit includes a clock driver that provides a differential clock signal to a clock slicer over a pair of transmission lines. The clock distribution circuit further includes a resistor-inductor-capacitor (RLC) tuning circuit for providing termination between the pair of transmission lines and a differential input to the clock slicer. The RLC tuning circuit includes a pair of resistor digital-to-analog converters (resistor DACs or RDACs) coupled to the pair of transmission lines and a pair of controllable inductor-capacitor (LC) circuits coupled to the pair of transmission lines.

A method for providing a high-speed data communication between a host and field-programmable gate array (“FPGA”) is disclosed. The method, in one embodiment, is capable of identifying a data rate on a bus containing a P-channel and an N-channel operable to transmit signals in accordance with a high-speed Universal Serial Bus (“USB”) protocol. Upon sampling, by a first input deserializer, first two samples of data signals carried by the P-channel in accordance with a first clock signals clocking twice as fast as the data rate of the P-channel, a second input deserializer is used to sample the second two samples of data signals transmitted by the N-channel in accordance with a second clock signal running twice as fast as the data rate of the N-channel with a ninety (90) degree phase shift. The method subsequently forwards the data signals to one or more configurable logic blocks (“LBs”) in FPGA.

A method for providing a high-speed data communication between a host and field-programmable gate array (“FPGA”) is disclosed. The method, in one embodiment, is capable of identifying a data rate on a bus containing a P-channel and an N-channel operable to transmit signals in accordance with a high-speed Universal Serial Bus (“USB”) protocol. Upon sampling, by a first input deserializer, first two samples of data signals carried by the P-channel in accordance with a first clock signals clocking twice as fast as the data rate of the P-channel, a second input deserializer is used to sample the second two samples of data signals transmitted by the N-channel in accordance with a second clock signal running twice as fast as the data rate of the N-channel with a ninety (90) degree phase shift. The method subsequently forwards the data signals to one or more configurable logic blocks (“LBs”) in FPGA.

In described examples, a pulse width modulation (PWM) system includes an initiator and a receiver. The initiator includes an initiator counter and an initiator PWM signal generator. The initiator counter advances an initiator count in response to an initiator clock signal. The initiator PWM signal generator generates an initiator PWM signal in response to the initiator count. The receiver includes a receiver counter, a receiver PWM signal generator, and circuitry configured to reset the receiver count. The receiver counter advances a receiver count in response to a receiver clock signal. The receiver PWM signal generator generates a receiver PWM signal in response to the receiver count. The circuitry resets the receiver count in response to a synchronization signal and based on an offset.

In described examples, a pulse width modulation (PWM) system includes an initiator and a receiver. The initiator includes an initiator counter and an initiator PWM signal generator. The initiator counter advances an initiator count in response to an initiator clock signal. The initiator PWM signal generator generates an initiator PWM signal in response to the initiator count. The receiver includes a receiver counter, a receiver PWM signal generator, and circuitry configured to reset the receiver count. The receiver counter advances a receiver count in response to a receiver clock signal. The receiver PWM signal generator generates a receiver PWM signal in response to the receiver count. The circuitry resets the receiver count in response to a synchronization signal and based on an offset.

A clock selector circuit receives a first input clock signal (CLK1) having a first frequency, and a second input clock signal (CLK2) having a second frequency. A phase difference detector is configured to detect when a phase difference occurs, over time, between the first input clock signal (CLK1) and the second input clock signal (CLK2), determined using when a clock edge crosses zero, and to signal this zero crossing to switching circuitry. The switching circuitry is configured, in response to receiving a zero-crossing signal from the phase difference detector, to detect an edge of opposite type to the predetermined type in the first input clock signal (CLK1) or in the second input clock signal (CLK2), and, in response to detecting said edge of opposite type, to switch an output clock signal (CLK_OUT) between the first input clock signal (CLK1) and the second input clock signal (CLK2).

A clock selector circuit receives a first input clock signal (CLK1) having a first frequency, and a second input clock signal (CLK2) having a second frequency. A phase difference detector is configured to detect when a phase difference occurs, over time, between the first input clock signal (CLK1) and the second input clock signal (CLK2), determined using when a clock edge crosses zero, and to signal this zero crossing to switching circuitry. The switching circuitry is configured, in response to receiving a zero-crossing signal from the phase difference detector, to detect an edge of opposite type to the predetermined type in the first input clock signal (CLK1) or in the second input clock signal (CLK2), and, in response to detecting said edge of opposite type, to switch an output clock signal (CLK_OUT) between the first input clock signal (CLK1) and the second input clock signal (CLK2).

A receiver for OFDM subcarriers has a first mode and a second mode. In the first mode, a tunable system clock is output at a nominal frequency, and in the second mode, the tunable system clock is offset so that a harmonic of the tunable system clock coincides with a particular OFDM subcarrier. The tunable system clock is coupled to a programmable modem PLL clock generator which generates clocks for an A/D converter coupled to a baseband processor which is also coupled to the programmable modem PLL clock generator. The programmable modem PLL clock generator is programmed to maintain a constant output frequency of each output in the first mode and the second mode.

A receiver for OFDM subcarriers has a first mode and a second mode. In the first mode, a tunable system clock is output at a nominal frequency, and in the second mode, the tunable system clock is offset so that a harmonic of the tunable system clock coincides with a particular OFDM subcarrier. The tunable system clock is coupled to a programmable modem PLL clock generator which generates clocks for an A/D converter coupled to a baseband processor which is also coupled to the programmable modem PLL clock generator. The programmable modem PLL clock generator is programmed to maintain a constant output frequency of each output in the first mode and the second mode.