AD6650SLASHPCB datasheet(15/45 Pages) AD

15 / 45 page

AD6650

Rev. A | Page 14 of 44

TERMINOLOGY

Analog Bandwidth

The analog input frequency at which the spectral power of the

fundamental frequency (as determined by the FFT analysis) is

reduced by 3 dB.

Noise Figure (NF)

The degradation in SNR performance (in dB) of an IF input

signal after it passes through a component or system.

The AD6650 noise figure is determined by the equation

⎟

⎠

⎞

⎜

⎝

⎛

−

⎟

⎠

⎞

⎜

⎝

⎛

−

⎟

⎠

⎞

⎜

⎝

⎛

001

log

001

log

kTB

SNR

rms

(1)

where:

k is the Boltzmann constant = 1.38 × 10−23.

T is the temperature in kelvin.

B is the channel bandwidth in hertz (200 kHz typical).

V2rms is the full-scale input voltage.

Zin is the input impedance.

SNRFS is the computed signal-to-noise ratio referred to full scale

with a small input signal and the AD6650 in maximum gain.

Input Second-Order Intercept (IIP2)

A figure of merit used to determine a component’s or system’s

susceptibility to intermodulation distortion (IMD) from its

second-order nonlinearities. Two unmodulated carriers at a

specified frequency relationship (f1 and f2) are injected into a

nonlinear system exhibiting second-order nonlinearities

producing IMD components at f1 − f2 and f2 − f1. IIP2

graphically represents the extrapolated intersection of the

carrier’s input power with the second-order IMD component

when plotted in decibels.

Input Third-Order Intercept (IIP3)

A figure of merit used to determine a component’s or system’s

susceptibility to intermodulation distortion (IMD) from its

third-order nonlinearities. Two unmodulated carriers at a

specified frequency relationship (f1 and f2) are injected into a

nonlinear system exhibiting third-order nonlinearities

producing IMD components at (2 × f1) – f2 and (2 × f2) – f1.

IIP3 graphically represents the extrapolated intersection of the

carrier’s input power with the third-order IMD component

when plotted in decibels.

Image

The AD6650 incorporates a quadrature demodulator that mixes

the IF frequency to a baseband frequency. The phase and amplitude

imbalance of this quadrature demodulator is observed in a complex

FFT as an image of the fundamental frequency. The term image

arises from the mirror-like symmetry of signal and image

frequencies about the beating-oscillator frequency (in this

case, this is dc).

Differential Analog Input Resistance, Differential Analog

Input Capacitance, and Differential Analog Input Impedance

The real and complex impedances measured at each analog

input port. The resistance is measured statically, and the

capacitance and differential input impedances are measured

with a network analyzer.

Differential Analog Input Voltage Range

The peak-to-peak differential voltage that must be applied to

the converter to generate a full-scale response. Peak differential

voltage is computed by observing the voltage on a single pin

and subtracting the voltage from the other pin, which is 180°

out of phase. The peak-to-peak differential voltage is computed

by rotating the phases of the inputs 180° and taking the peak

measurement again. Then the difference is computed between

both peak measurements.

Full-Scale Input Power

Expressed in dBm. It is computed using the following equation:

⎟

⎠

⎞

⎜

⎝

⎛

001

log

Input

scale

Full

scale

Full

Power

rms

(2)

where ZInput is the input impedance.

Noise

The noise, including both thermal and quantization noise, for

any range within the ADC is computed as

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

−

001

dBFS

dBc

dBm

Signal

SNR

noise

(3)

where:

Z is the input impedance.

FSdBm is the full scale of the device for the frequency in question.

SNRdBc is the value for the particular input level.

SignaldBFS is the signal level within the ADC reported in decibels

below full scale.

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