TDA5200_10 INFINEON [Infineon Technologies AG], TDA5200_10 Datasheet - Page 22

• Manufacturer Part Number: TDA5200_10
• Description: ASK Single Conversion Receiver
• Manufacturer: INFINEON [Infineon Technologies AG]

4
4.1
In the following figure the internal circuitry of the LNA automatic gain control is shown.
Figure 5
The LNA automatic gain control circuitry consists of an operational transimpedance amplifier that is used to
compare the received signal strength signal (RSSI) generated by the Limiter with an externally provided threshold
voltage
typically 0.8 V and 2.8 V to provide a switching point within the receive signal dynamic range.
This voltage
voltage divider between the 3VOUT pin (Pin 24) which provides a temperature stable 3 V output generated from
the internal bandgap voltage and the THRES pin. If the RSSI level generated by the Limiter is higher than
the OTA generates a positive current
generates a negative current. These currents do not have the same values in order to achieve a fast-attack and
slow-release action of the AGC and are used to charge an external capacitor which finally generates the LNA gain
control voltage.
Data Sheet
U
thres
Applications
Choice of LNA Threshold Voltage and Time Constant
LNA Automatic Gain Control Circuitry
U
. As shown in the following figure the threshold voltage can have any value between approximately
thres
is applied to the THRES pin (Pin 23). The threshold voltage can be generated by attaching a
RSSI > U
RSSI < U
threshold
threshold
Pins:
: I
: I
load
load
=4.2µA
= -1.5µA
I
load
C
24
4
. This yields a voltage rise on the TAGC pin (Pin 4). Otherwise, the OTA
+3V
U
I
C
load
R4
U
U
U
U
c
c
cmax
cmin
:< 2.6V : Gain high
:> 2.6V : Gain low
23
22
= V
= 1.67V
OTA
CC
U
threshold
- 0.7V
Gain control
R5
voltage
V
CC
RSSI (0.8 - 2.8V)
ASK Single Conversion Receiver
LNA
Revision 3.0, 2010-12-28
Applications
TDA 5200
U
thres
,