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STA002

STARMAN™ CHANNEL DECODER

STMicroelectronics 

STA002

TABLE 2. Carrier loop parameters (m = 22; KD = 1.26; M_CLK = 39.02687179MHz)

beta_car

fn(KHz)

alpha_car

0

1

2

3

4

5

6

7

8

9

10

NA 0.38 0.54 0.77 1.09 1.54 2.17 3.07 4.35 6.15 8.69

Damping factor

0 NA NA NA NA NA NA NA NA NA NA NA

1 NA 0.67 0.47 0.34 0.24 0.17 0.12 0.08 0.06 0.04 0.03

2 NA 1.34 0.95 0.67 0.47 0.34 0.24 0.17 0.12 0.08 0.06

3 NA 2.69 1.90 1.34 0.95 0.67 0.47 0.34 0.24 0.17 0.12

4 NA 5.37 3.80 2.69 1.90 1.34 0.95 0.67 0.47 0.34 0.24

5 NA 10.7 7.60 5.37 3.80 2.69 1.90 1.34 0.95 0.67 0.47

order system controlled by two parameters, al-

pha-car and beta-car, contained in the

CARFLTPAR register.

The natural frequency and the damping factor are

given in the following formulas:

Phase Detector Gain

(Kd)

D97AU725

fn = √mKoKD β

2π

where β is programmed by the carrier register

beta_car:

β = 2beta_car-4 ⋅Fsym (Fsym = 1.84MHz)

m is the reference value of the AGC2 loop (see

AGC2_REF register), KD is the phase detector

gain and Ko is the constant of the carrier NCO:

1.2

1

0.8

0.6

0

0

5

10

C/N(dB)

Ko

=

2π

226

FCK

The damping factor is

ξ

=

α

2

√mKoKD

β

where α is programmed by the carrier register al-

pha_car:

α = 2alpha_car+6

beta_car can only take value from 0 to 15; if

beta_car is 0 the loop becames a first order one.

alpha_car can take any value from 0 to 9. If both

alpha_car and beta_car are 0 then the loop is

open.

KD depends on the signal to noise ratio and is

given in the figure in next column.

(see par. 3.8 for C/N definition)

KD = 1.26 for a noise free input signal.

The natural frequency and the damping factor

can be rewritten as:

fn = 16.515 √FCK √m⋅KD⋅ 2beta_car

√ ξ = 0.0289 √FCK 2alpha_car

m ⋅ KD

2beta_car

Table 2 gives the natural frequency and the

damping factor for the nominal amplitude m = 22,

KD = 1.26 and M_CLK = 39.02687179MHz.

In presence of noise the value of KD may be re-

duced of up to 60%; it is recommended to start

with a damping factor, without noise, greater than

the usual value of 0.7.

3.4.3 Phase and frequency detector parameter

The carrier phase error is calculated by the fol-

lowing formula : ε = I sgn(Q) - Q sgn(I).

This value is computed (at symbol rate) if the ac-

tual I and Q components are greater than a pro-

grammed threshold otherwise the previous value

is mantained. In this way the detector outputs a

DC value proportional to the frequency offset be-

tween the incoming signal and the local oscillator.

The threshold value may be programmed by the

PFDTHR parameter inside the QPSK_CON-

TROL2 register:

18/43

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