STA002 datasheet(21/43 Pages) STMICROELECTRONICS

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The relation between C/N and the required value

(CNCNT) is given in the table 3 for three AGC2

reference levels. A value of 255 means overflow.

3.8.2 Control Register

There are two parameters to control the C/N esti-

mator circuit CNTHR and SN located in the

QPSK _CONTROL 2 register.

The CNTHR parameter (2 bits) sets the threshold

value under which the circuit is activated.

The SN parameter (2bits) sets the measure time

internal.

Both there two parameters are given in the fol-

lowing tables:

CNTHR

THRESHOLD

TIME INTERVAL IN SYMBOLS

1024

4096

16384

65536

A suitable value of the threshold and time inter-

val must be chosen to have a good level of confi-

dence of the C/N estimate.

To increase the measure accuracy is advisable to

average several values.

Before starting the measure the CNCNT register

must be reset and can be read after the selected

time internal.

A flag bit (CNFLAG) is set to 1 to indicate that a

value is available in the CNCNT register.

3.9 CONTROL REGISTERS

QPSK_CONTROL1 register

Internal address: 80 H

Reset Value: 10H

MSB

LSB

b6b5b4b3

b6 : AGC1CHS

b5 : CAR CHS

b4 :TIMCHS

b3 : QCHP

AGC1CHS changes the polarity of the AGC sig-

nal at output pin.

CARCHS and TIMCHS change the sign of the

carrier tracking loop and symbol tracking loop re-

spectively.

QCHS inverts the sign of the Q component.

QPSK_CONTROL2 register

Internal address: 81 H

Reset Value: 90H

MSB

LSB

PFDTHR

CNTHR

TABLE 3. Correspondence between C/N and the CNCNT register contents.

C/N(dB)

Eb/No|QPSK

CNTHR = 8

CNTHR = 12

CNTHR = 16

m = AGC2_ REF

161

155

148

140

132

122

113

105

121

112

102

3.4

2.4

1.5

0.9

101

3.2

1.6

0.9

0.5

0.25

0.07

177

173

168

161

155

148

141

134

125

118

112

103

151

145

138

130

120

110

100

193

192

190

186

184

180

177

174

170

165

161

158

154

149

144

141

137

131

The value are the average of 1000 readings of the CNCNT register.

STA002

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