AD9545 datasheet(128/157 Pages) AD

128 / 157 page

AD9545

Data Sheet

Rev. A | Page 128 of 157

For example, convert C0 = 1.0046936 × 10−3 to its corresponding

bit field value.

Constant CV = C0/2−45

= 1.0046936 × 10−3/2−45

= 35,349,513,305 (nearest integer)

= 0x083AFEC459 (hexadecimal)

C1 through C5 apply scale factors to corresponding powers

of T. Program the C1 through C5 coefficients via the signed

(twos complement) 16-bit Tx significand (Register 0x028E

to Register 0x28F, Register 0x0291 to Register 0x0292,

and signed (twos complement) 8-bit Tx exponent bit fields

(Register 0x0290, Register 0x0293, Register 0x0296,

to the coefficient subscript.

The C1 through C5 coefficients have the following format:

Cx = Sx × 2Ex

where:

Sx is the signed integer associated with the Tx significand bit

fields.

Ex is the signed integer associated with the Tx

exponent bit

fields. In practice, Coefficient C1 to Coefficient C5 are Base 10

numbers. The following procedure explains how to convert

Base 10 numbers to the necessary bit field format for C1 to C5.

There are three cases for Cx.

•

The trivial case (Cx = 0)

•

The case where Cx is less than the quantization limit

•

The case where Cx is greater than the quantization limit

For the first two cases (that is, Cx = 0 or Cx is less than the

quantization limit),

Tx Significand = 0 (0x0000 hexadecimal)

Tx Exponent = 0 (0x00 hexadecimal)

To test if Cx is less than the quantization limit, check whether

the following inequality is true:

127

log

−

(25)

Log(x) is the logarithm of x (ln(x), log2(x), log10(x), for

example), |x| is the absolute value of x, and

⌊x⌋isthenotation

for signifying the nearest integer to x in the direction of −∞.

If Cx is nonzero and the inequality in Equation 25 is false, then

ExpVal =

log |

log 2

+ 1

Tx Exponent = ExpVal

Tx Significand = round(iCx × 215 − ExpVal)

where round() means round to the nearest integer.

Using C1 as an example, convert Coefficient C1 = −2.8927765 ×

10−6 to its corresponding bit field values. First, check that C1 is

greater than the quantization limit.

C1_ExpVal =

log

8927765

log













−

= −18

This value is greater than the quantization limit of −127.

Therefore,

T1 exponent = C1_ExpVal = −18

= 0xEE (hexadecimal)

T1 significand = round(C1 × 215 − C1_ExpVal)

= round(−2.8927765 × 10−6 × 215 − (−18))

= −24,849

= 0x9EEF (hexadecimal)

Using C2 as an example, convert Coefficient C2 = –1.9110192 ×

10−7 to its corresponding bit field values. First, check that C2 is

greater thna the quantization limit.

C2_ExpVal =

log

9110192

log













−

= −22

This vaue is greater than the quantization limit of −127.

Therefore,

T2 Exponent = C2_ExpVal = −22

= 0xEA (hexadecimal)

T2 Significand = round(C2 × 215 − C2_ExpVal)

= round(−1.9110192 × 10−7 × 215 − (−22))

= −26,265

= 0x9967 (hexadecimal)

Using C3 as an example, convert Coefficient C3 = 2.2493907 ×

10−9 to its corresponding bit field values. First, check that C3 is

greater than the quantization limit.

C3_ExpVal =

log













log

2493907

log













× −

= −28

This value is greater than the quantization limit of −127.

AD9545 Datasheet(PDF) 128 Page - Analog Devices

AD9545 Datasheet(HTML) 128 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL