TDA7200 Datasheet, PDF (19/49 Pages) Infineon Technologies AG – ASK/FSK Single Conversion Receiver

TDA7200
3
Applications
Applications
3.1
Application Circuit
C18
R4
R5
3VOUT
24
20kΩ
THRES
U_threshold
23
RSSI (0.8 - 2.8V)
+3.1 V
OTA
VCC
RSSI > U_threshold: I_load=4.2µA
RSSI < U_threshold: I_load= -1.5µA
I_load
4
LNA
Gain control
voltage
TAGC
U_C
U_c:< 2.6V : Gain high
U_c:> 2.6V : Gain low
C5
U_cmax= V_CC - 0.7V
U_cmin = 1.67V
Figure 3 LNA Automatic Gain Control Circuity
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 U_thres. As shown in the
following figure the threshold voltage can have any value between approximately 0.8 and
2.8V to provide a switching point within the receive signal dynamic range.
This voltage U_thres is applied to the THRES pin (Pin 23) The threshold voltage can be
generated by attaching a voltage divider between the 3VOUT pin
(Pin 24) which provides a temperature stable 3V output generated from the internal
bandgap voltage and the THRES pin. If the RSSI level generated by the Limiter is higher
than U_thres, the OTA generates a positive current I_load. This yields a voltage rise on the
TAGC pin (Pin 4). Otherwise, the OTA 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
Data Sheet
19
V 1.0, 2007-05-02