ADMV8505ACCZ-R7 datasheet(12/31 Pages) AD

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Data Sheet

ADMV8505

THEORY OF OPERATION

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Rev. 0 | 12 of 31

INTERPOLATION EQUATIONS

The following equations describe the input to the interpolation

functions:

fCMIN=minfCENTER

(1)

fCMAX=maxfCENTER

(2)

fCSTEP≈fCMAX−fCMIN

255

(3)

x=FC_LOAD_X, Bits7:0

(4)

The anticipated fCENTER of the filter is then computed as follows:

fCENTER≈fCMIN+fCSTEP×x

(5)

The equations for the interpolation function of y = f(x) that deter-

mines the capacitor codes (CFC) are shown in Table 6.

Table 6. Equations for y = f(x)

Condition

Logic Shift Form1

If (0 ≤ x < 16)

y = Y1 +(((16 − x)(Y0 − Y1)) >> 4)

If (16 ≤ x < 32)

y = Y2 +(((32 − x)(Y1 − Y2)) >> 4)

If (32 ≤ x < 64)

y = Y3 +(((64 − x)(Y2 − Y3)) >> 5)

If (64 ≤ x < 96)

y = Y4 +(((96 − x)(Y3 − Y4)) >> 5)

If (96 ≤ x < 128)

y = Y5 +(((128 − x)(Y4 − Y5)) >> 5)

If (128 ≤ x < 160)

y = Y6 +(((160 − x)(Y5 − Y6)) >> 5)

If (160 ≤ x < 192)

y = Y7 +(((192 − x)(Y6 − Y7)) >> 5)

If (192 ≤ x < 224)

y = Y8 +(((224 − x)(Y7 − Y8)) >> 5)

If (224 ≤ x < 255)

y = Y9 +(((256 − x)(Y8 − Y9)) >> 5)

Else

y = Y9

1 Y0 to Y9 are the fCENTER coefficients.

The equations for the interpolation function of v = f(y) that deter-

mines the bandwidth capacitor codes (CBW) are shown in Table 7.

Table 7. Equations for v = f(y)

Condition

Logic Shift Form1

If (0 ≤ y < 32)

v = V0 + ((y × (V1 − V0)) >> 5)

If (32 ≤ y < 255)

v = V1 + (((y − 32) (V2 − V1) × 295) >> 16)

Else

v = V2

1 Y0 to Y2 are the bandwidth coefficients.

The equations for the interpolation function of t = f(y) that deter-

mines the match capacitor codes (CMATCH) are shown in Table 8.

Table 8. Equations for t = f(y)

Condition

Logic Shift Form1

If (0 ≤ y < 32)

t = T0 + ((y × (T1 − T0)) >> 5)

If (32 ≤ y < 255)

t = T1 + (((y − 32) (T2 − T1) × 295) >> 16)

Else

t = T2

1 T0 to T2 are the match coefficients.

INTERPOLATION TABLES

Solving the interpolation equations for the lower bounds of each

condition in the interpolation function of y = f(x) yields what is

detailed in Table 9.

Table 9. Equations for Anticipated fCENTER for Each Significant x Value

fCENTER

y = f(x)

fCENTER ≈ fCMIN

fCENTER ≈ fCMIN + fCSTEP × 16

fCENTER ≈ fCMIN + fCSTEP × 32

fCENTER ≈ fCMIN + fCSTEP × 64

fCENTER ≈ fCMIN + fCSTEP × 96

128

fCENTER ≈ fCMIN + fCSTEP × 128

160

fCENTER ≈ fCMIN + fCSTEP × 160

192

fCENTER ≈ fCMIN + fCSTEP × 192

224

fCENTER ≈ fCMIN + fCSTEP × 224

255

fCENTER ≈ fCMAX

Similarly, solving the equations for the lower bounds of each condi-

tion in the interpolation functions of v = f(y) and t = f(y) yields what

is detailed in Table 10.

Table 10. Equations for v = f(y) and t = f(y) for Each Significant y Value

v = f(y)

t = f(y)

255

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