ADMV8505ACCZ-R7 datasheet(13/31 Pages) AD

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Data Sheet

ADMV8505

THEORY OF OPERATION

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Rev. 0 | 13 of 31

INTERPOLATION PLOTS

To garner a visual representation of the interpolation functions,

the interpolation coefficients vs. their input (from the interpolation

tables) can be plotted on a scatter plot. Figure 23, Figure 24, and

Figure 25 are the interpolation functions of y, v, and t using the

interpolation coefficients.

Figure 23. Interpolation Function of y = f(x)

Figure 24. Interpolation Function of v = f(y)

Figure 25. Interpolation Function of t = f(y)

INTERPOLATION COEFFICIENT CALIBRATION

The two primary reasons for the need to calibrate the interpolation

coefficients include accounting for chip process variation and a dif-

ferent required operating bandwidth. The calibration of interpolation

coefficients normally follows a four phase process (see Figure 27).

In the first calibration phase, the bandwidth and match coefficients,

V1 and T1, are determined for a desired bandwidth. To perform

this calibration phase, the fCENTER load value must be set to 32.

Then, the bandwidth and match load values are adjusted. When

satisfied with the results, the V1 and T1 coefficients can be set to

the bandwidth and match load values, respectively.

For the second calibration phase, the bandwidth and match coeffi-

cients, V2 and T2, are determined for a desired bandwidth. To

perform this calibration phase, the fCENTER load value must be set

to a high value (180 is recommended). Then, the bandwidth and

match load values are adjusted. When satisfied with the results, the

V2 coefficient can be adjusted so that the computed result of v =

f(y) = f(180) is equal to the bandwidth load value. Similarly, the T2

coefficient can be adjusted so that the computed result of t = f(y) =

f(180) is equal to the match load value.

For the third calibration phase, the bandwidth and match coeffi-

cients, V0 and T0, are determined for a desired bandwidth. To

perform this calibration phase, the fCENTER load value must be set

to a low value (18 is recommended). Then, the bandwidth and

match load values are adjusted. When satisfied with the results, the

V0 coefficient can be adjusted so that the computed result of v =

f(y) = f(18) is equal to the bandwidth load value. Similarly, the T0

coefficient can be adjusted so that the computed result of t = f(y) =

f(18) is equal to the match load value.

For the fourth calibration phase, adjustments are made to all of the

y coefficients to ensure the operating fCENTER is as close as possi-

ble to the anticipated fCENTER. To perform this calibration phase, use

Table 9 as a reference for determining the target frequency for each

y coefficient. For each x value listed in Table 9, compute the y, v,

ADMV8505ACCZ-R7 Datasheet(PDF) 13 Page - Analog Devices

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