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ADA2200

Data Sheet

APPLICATIONS INFORMATION

The signal present at the output of the ADA2200 depends on

the amplitude and relative phase of the signal applied at it inputs.

When the amplitude or phase is known and constant, any

output variations can be attributed to the modulated parameter.

Therefore, when the relative phase of the input is constant, the

ADA2200 performs amplitude demodulation. When the amplitude

is constant, the ADA2200 performs phase demodulation.

The sampling and demodulation processes introduce additional

frequency components onto the output signal. If the output

signal of the ADA2200 is used in the analog domain or if it is

sampled asynchronously to the ADA2200 sample clock, these high

frequency components can be removed by following the

ADA2200 with a reconstruction filter.

If the ADA2200 output is sampled synchronously to the

ADA2200 output sample rate, an analog reconstruction filter is

not required because the ADC inherently rejects sampling

artifacts. The frequency artifacts introduced by the

demodulation process can be removed by digital filtering.

AMPLITUDE MEASUREMENTS

If the relative phase of the input signal to the ADA2200 remains

constant, the output amplitude is directly proportional to the

amplitude of the input signal. Note that the signal gain is a

function of the relative phase of the input signal. Figure 15 shows

the relationship between the cycle mean output and the relative

phase. The cycle mean output voltage is

VCYCLEMEAN = Conversion Gain × VIN(RMS) × sin(θREL − θDEL) =

1.05 ×VIN(RMS) × sin(θREL − θDEL)

Therefore, the highest gain, and thus the largest signal-to-noise

ratio measurement, is obtained when operating the ADA2200

with θREL = θDEL + 90° = 173°. This value of θREL is also the

operating point with the lowest sensitivity to changes in the

relative phase. Operating with θREL = θDEL − 90° = −7° offers the

same gain and measurement accuracy, but with a sign inversion.

PHASE MEASUREMENTS

If the amplitude of the input signal to the ADA2200 remains

constant, the output amplitude is a function of the relative

phase of the input signal. The relative phase can be measured as

θREL = sin−1(VCYCLEMEAN/(Conversion Gain × VIN(RMS))) + θDEL =

sin−1(VCYCLEMEAN/(1.05 × VIN(RMS))) + θDEL

Note that the output voltage scales directly with the input signal

amplitude. A full-scale input signal provides the greatest phase

sensitivity (V/°θREL) and thus the largest signal-to-noise ratio

measurement.

The phase sensitivity also varies with relative phase. The

sensitivity is at a maximum when θREL = 83°. For this reason, the

optimal measurement range is for input signals with a relative

phase equal to the phase delay of ±45°. This range provides the

highest gain and thus the largest signal-to-noise ratio

measurement. This range is also the operating point with the

lowest sensitivity to changes in the relative phase. Operating at a

relative phase equal to the phase delay of −135° to −225° offers

the same gain and measurement accuracy, but with a sign

inversion.

The phase sensitivity with a 4 V p-p differential input operating

with a relative phase that is equal to the phase delay results in a

phase sensitivity of 36.6 mV/°θREL.

AMPLITUDE AND PHASE MEASUREMENTS

When both the amplitude and relative phase of the input signals

are unknown, it is necessary to obtain two orthogonal

components of the signal to determine its amplitude, relative

phase, or both. These two signal components are referred to as

the in-phase (I) and quadrature (Q) components of the signal.

A signal with two known rectangular components is represented as

a vector or phasor with an associated amplitude and phase (see

Figure 25).

Figure 25. Rectangular and Polar Representation of a Signal

If the signal amplitude remains nearly constant for the duration

of the measurement, it is possible to measure both the I and the

Q components of the signal by toggling the PHASE90 bit

between two consecutive measurements. To measure the I

component, set the PHASE90 bit to 0. To measure the Q

component, set the PHASE90 bit to 1.

After both the I and Q components have been obtained, it is

possible to separate the effects of the amplitude and phase

variations. Then, calculate the magnitude and relative phase

using the following formulas:

DEL

REL









–

cos

Or alternatively

DEL

REL









–

sin

III

Rev. 0 | Page 16 of 24

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