AD6676EBZ datasheet(22/90 Pages) AD

22 / 90 page

AD6676

Data Sheet

Rev. A | Page 22 of 90

TERMINOLOGY

Noise Figure (NF)

NF is the degradation in SNR performance (in dB) of an input

signal having a noise density of −174 dBm/Hz after it passes

through a component or system. Mathematically,

NF = 10 × log(SNRIN/SNROUT)

The noise figure of the AD6676 is determined by the equation

NF = PIN − (10 × log(BW)) − (−174.0 dBm/Hz) − SNR

where:

PIN is the input power of an unmodulated carrier.

BW is the noise measurement bandwidth.

−174.0 dBm/Hz is the thermal noise floor at 290 K.

SNR is the measured signal-to-noise ratio in dB of the AD6676.

Note that PIN is set to a low level (that is, <−40 dBm) to

minimize any degradation in measured SNR due to phase noise

from either the input signal or Σ-Δ ADC clock source.

Noise Spectral Density (NSD)

NSD is the noise power normalized to 1 Hz bandwidth (at a

particular frequency) relative to the full scale of the ADC (dBFS)

and hence is given in units of dBFS/Hz. The AD6676, being a

Σ-Δ ADC, displays a uneven NSD across its IF pass band. Both

the worst-case NSD as well as NSD at the pass band center are

reported. Note that NSD is calculated from the IBN measured

over a 5 MHz bandwidth.

In-Band Noise (IBN)

IBN is the integrated noise power measured over a user defined

bandwidth relative to the full scale of the ADC (dBFS). This

bandwidth is typically equal to the IF pass band setting (BW) of

the AD6676, unless otherwise noted.

Input Second-Order Intercept (IIP2)

IIP2 is a figure of merit used to quantify the second-order

intermodulation distortion (IMD2) of a component or system.

Two equal amplitude unmodulated carriers at specified

frequencies (f1 and f2) injected into a nonlinear system exhibiting

second-order nonlinearities produce IMD components at f1 − f2

and f1 + f2. For the AD6676, the two frequencies are situated

at ½ the IF frequency (with a 2 MHz offset) at a power level

corresponding to −6 dBFS at the IF center frequency with

only the intermodulation term at f1 + f2 considered. IIP2 is

the extrapolated tone power at which the intermodulation

terms and the input tones have equal amplitude.

IIP2 = PIN − IMD2

Input Third-Order Intercept (IIP3)

IIP3 is a figure of merit used to quantify the third-order

intermodulation distortion (IMD3) of a component or system.

Two equal amplitude unmodulated carriers at specified frequencies

(f1 and f2) injected into a nonlinear system exhibiting third-order

nonlinearities produce IMD components at 2 f1 − f2 and 2 f2 − f1.

IIP3 is the extrapolated tone power at which the intermodulation

terms and the input tones have equal amplitude.

IIP3 = PIN – IMD3/2

Note that the third-order IMD performance of an ADC does

not necessarily follow the 3:1 rule that is typical of RF/IF linear

devices. IMD performance is dependent on the dual tone

frequencies, signal input levels, and ADC clock rate.

Worst In-Band Spur (SFDR)

Worst in-band spur is the worst spur falling in the IF pass band

relative to the full scale of the ADC (dBFS) when a single tone

with defined power level is stepped (typically 1 MHz increments)

across a user defined frequency range. Note that this worst spur

can often be an image (or clock) related spur depending on the

IF, BW, and IQ output data rate setting of the AD6676 and on

the sweep range.

Signal Transfer Function (STF)

STF is the frequency response of the output signal of the ADC

relative to a swept single tone at its input. The STF presented for

different AD6676 setup conditions in the Typical Performance

Characteristics section shows the STF over the IF pass band

after the digital filter to highlight pass band flatness. The

wideband STF response is measured before the digital filter to

highlight the pass band response of the AD6676 Σ-Δ ADC.

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