TDA5220 Datasheet, PDF (17/44 Pages) Infineon Technologies AG – ASK/FSK Single Conversion Receiver

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3.3 Functional Block Diagram
TDA 5220
preliminary
Functional Description
VCC
IF
Filter
MSEL
H=ASK
L=FSK
LNO
MI
MIX IFO
LIM
LIMX
FFB
OPP
SLP
SLN
6
8 9 12
17 18
15
RF
LNI
3 _LNA
TAGC
4
TDA 5220
LIMITER
FSK
PLL Demod
-
+ FSK
- _ASK
+
22
21
19
20
16 SSEL
Logic
-
+ CM
25 _DATA
+ CP
-
DATA-
OP
SLICER
PEAK
DETECTOR
PDO
26
OTA
23 THRES
VCC
14
DGND
13
2,7 5,10
:1
:2
VCO
: 64
Φ
DET
Loop
Filter
11
CRYSTAL
OSC
1
28
U _REF
AGC
Reference
Bandgap
Reference
27
24 3VOUT
VCC AGND
FSEL
Crystal
Figure 3-2 Main Block Diagram
PDWN
Function_5220.wmf
3.4 Functional Blocks
3.4.1 Low Noise Amplifier (LNA)
The LNA is an on-chip cascode amplifier with a voltage gain of 15 to 20dB. The
gain figure is determined by the external matching networks situated ahead of
the LNA and between the LNA output LNO (Pin 6) and the Mixer Inputs MI and
MIX (Pins 8 and 9). The noise figure of the LNA is approximately 3dB and the
current consumption is 500µA. The gain can be reduced by approximately
18dB. The switching point of this AGC action can be determined externally by
applying a threshold voltage at the THRES pin (Pin 23). This voltage is com-
pared internally with the received signal (RSSI) level generated by the limiter
circuitry. In case that the RSSI level is higher than the threshold voltage the LNA
gain is reduced and vice versa. 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 as described in Section 4.1. The time constant of the AGC
action can be determined by connecting a capacitor to the TAGC pin (Pin 4) and
should be chosen along with the appropriate threshold voltage according to the
Wireless Components
3-9
Target Specification, October 2001