参数资料
型号: IP-NCO
厂商: Altera
文件页数: 34/54页
文件大小: 0K
描述: IP NCO COMPILER
标准包装: 1
系列: *
类型: MegaCore
功能: 数控振荡器编译器
许可证: 初始许可证
4–2
Chapter 4: Functional Description
Avalon-ST and Avalon-MM Interfaces
The SFDR of a digital sinusoid is the power of the primary or desired spectral
component relative to the power of its highest-level harmonic component in the
spectrum. Harmonic components manifest themselves as spikes or spurs in the
spectral representation of a digital sinusoid and occur at regular intervals and are also
a direct consequence of finite precision. However, the effect of the spurs is often
severe because they can cause substantial inter-modulation products and undesirable
replicas of the mixed signal in the spectrum, leading to poor reconstruction of the
signal at the receiver.
The direct effect of finite precision varies between architectures, but the effect is
augmented because, due to resource usage constraints, the NCO does not usually use
the full accumulator precision in the polar-to-cartesian transformation. You can
mitigate truncation effects with phase dithering, in which the truncated phase value is
randomized by a sequence. This process removes some of the periodicity in the phase,
reducing the spur magnitude in the sinusoidal spectrum by up to 12 dB.
The NCO MegaCore function’s graphical spectral analysis allows you to view the
effects as you change parameters without regenerating the IP Toolbench output files
and re-running simulation.
Refer to “Setting Parameters” on page 3–1 for information about how you can view
the effects of changing the generation algorithm, precision, phase dithering and
generated output frequency parameters.
Maximum Output Frequency
The maximum frequency sinusoid that an NCO can generate is bounded by the
Nyquist criterion to be half the operating clock frequency. Additionally, the
throughput affects the maximum output frequency of the NCO. If the NCO outputs a
new set of sinusoidal values every clock cycle, the maximum frequency is the Nyquist
frequency. If, however, the implementation requires additional clock cycles to
compute the values, the maximum frequency must be further divided by the number
of cycles per output.
Avalon-ST and Avalon-MM Interfaces
The Avalon-ST interface defines a standard, flexible, and modular protocol for data
transfers from a source interface to a sink interface and simplifies the process of
controlling the flow of data in a datapath.
Avalon-ST interface signals can describe traditional streaming interfaces supporting a
single stream of data without knowledge of channels or packet boundaries. Such
interfaces typically contain data, ready, and valid signals. The NCO MegaCore
function is an Avalon-ST source and does not support backpressure.
The Avalon-MM interface provides a means to control the frequency hopping feature
at run time.
f For more information about the Avalon-MM and Avalon-ST interfaces including
integration with other Avalon-ST components which may support backpressure, refer
to the Avalon Interface Specifications .
NCO MegaCore Function
User Guide
November 2013 Altera Corporation
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