CLC5902 datasheet(17/28 Pages) NSC

17 / 28 page

Rev. 3.05 May 27, 1999

Overall Channel Gain

The overall gain of the chip is a function of the amount of

decimation (N), the settings of the “SHIFT UP” circuit

(SCALE), the GAIN setting, the sum of the F1 coeffi-

cients, and the sum of the F2 coefficients. The overall gain

is shown below in Equation 2.

EQ. 2

Where:

EQ. 3

and:

EQ. 4

It is assumed that the DDC output words are treated as

fractional 2’s complement words. The numerators of

and

equal the sums of the impulse response coeffi-

cients of F1 and F2, respectively. For the STD and GSM

sets,

and

are nearly equal to unity. Observe that

the

term in EQ. 2 is cancelled by the DVGA oper-

ation so that the entire gain of the DRCS is independent of

the DVGA setting when EXP_INH=0. The

appearing in

EQ. 2 is the result of the 6dB conversion loss in the mixer.

For full-scale square wave inputs the

should be set to 1

to prevent signal distortion.

Data Latency and Group Delay

The latency from a sync event to data output is approxi-

mately 8N CK periods for F2 decimation by 2 and 24N

CK periods for F2 decimation by 4. Actual non-zero data

output can be further delayed depending on the F1 and F2

filter coefficients.

Group Delay is approximately 90N CK periods for F2

decimation by 2 or 4.

Figure 25

CIC, F1, & F2 STD Passband Flatness

100

150

200

250

−0.1

−0.08

−0.06

−0.04

−0.02

0.02

0.04

0.06

0.08

0.1

Combined Frequency Response of CIC/F1/F2 Using STD Set

Frequency (KHz)

Figure 26

CIC, F1, & F2 GSM frequency response

500

1000

1500

2000

2500

3000

−100

−80

−60

−40

−20

Combined Frequency Response of CIC/F1/F2 Using GSM Set

Frequency (KHz)

FCK = 52MHz

Decimation = 192

OFS = 270.83kHz

Figure 27

CIC, F1, & F2 GSM Passband Flatness

100

−2

−1.5

−1

−0.5

0.5

Combined Frequency Response of CIC/F1/F2 Using GSM Set

Frequency (KHz)

DDC

--- DEC

()

SCALE

–

AGAIN

EXP_INH

–

()

⋅

–

[]

GAIN

⋅

⋅⋅

1 i

()

∑

----------------------

2 i

()

∑

----------------------

AGAIN

---

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