參數(shù)資料
型號: MC1310
廠商: Motorola, Inc.
英文描述: CONNECTOR KIT, JPS130PS; RoHS Compliant: Yes
中文描述: 通用窄帶調(diào)頻接收器集成電路
文件頁數(shù): 30/68頁
文件大小: 1316K
代理商: MC1310
MC13110A/B MC13111A/B
30
MOTOROLA ANALOG IC DEVICE DATA
RSSI and Carrier Detect
The Received Signal Strength Indicator (RSSI) indicates
the strength of the IF level. The output is proportional to the
logarithm of the IF input signal magnitude. RSSI dynamic
range is typically 80 dB. A 187 k
resistor to ground is
provided internally to the IC. This internal resistor converts
the RSSI current to a voltage level at the “RSSI” pin. To
improve the RSSI accuracy over temperature an internal
compensated reference is used. Figure 56 shows the RSSI
versus RF input. The slope of the curve is 16.5 mV/dB.
The Carrier Detect Output (CD Out) is an open–collector
transistor output. An external pull–up resistor of 100 k
will
be required to bias this device. To form a carrier detect filter a
capacitor needs to be connected from the RSSI pin to
ground. The carrier detect threshold is programmable
through the MPU interface (see “Carrier Detect Threshold
Programming” in the serial interface section). The range can
be scaled by connecting additional external resistance from
the RSSI pin to ground in parallel with the capacitor. From
Figure 57, the affect of an external resistor at RSSI on the
carrier detect level can be noticed. Since there is hysteresis
in the carrier detect comparator, one trip level can be found
when the input signal is increased while the another one can
be found when the signal is decreased.
Figure 58 represents the RSSI ripple in relation to the RF
input for different filtering capacitors at RSSI. Clearly, the
higher the capacitor, the less the ripple. However, at low
carrier detect thresholds, the ripple might supersede the
hysteresis of the carrier detect. The carrier detect output may
appear to be unstable. Using a large capacitor will help to
stabilize the RSSI level, but RSSI charge time will be
affected. Figure 59 shows this relationship.
The user must decide on a compromise between the RSSI
ripple and RSSI start–up time. Choose a 0.01
μ
f capacitor as
a starting point. For low carrier detect threshold settings, a
0.047
μ
f capacitor is recommended.
–60
RSSI AND CARRIER DETECT
0
–120
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
–100
–80
–60
–40
–20
0
Mix1 In, RF INPUT (dBm)
Figure 56. Typical RSSI Voltage
Level versus RF Input
R
–90
–80
–70
–50
–40
–30
–20
0
100
1000
RRSSI, LOAD RESISTANCE (k
)
Figure 57. Carrier Detect Threshold versus
External RSSI Resistor
–10
Decreasing Signal
Limiter Input
Mixer 1
Input
Increasing Signal
Decreasing Signal
Increasing Signal
M
0
–120
1.0
2.0
3.0
4.0
5.0
6.0
7.0
11
10
–110
–100
–90
–80
–70
–60
Mix1 In, RF INPUT (dBm)
Figure 58. RSSI Ripple versus RF Input Level for
Different RSSI Capacitors
0
0.01
5.0
10
15
20
25
35
0.10
CRSSI, LOAD CAPACITANCE (
μ
F)
Figure 59. RSSI Charge Time
versus Capacitor Value
30
R
8.0
9.0
10 nF
22 nF
33 nF
47 nF
100 nF
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
R
1
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