tda5225 Infineon Technologies Corporation, tda5225 Datasheet - Page 29

• Manufacturer Part Number: tda5225
• Description: Enhanced Sensitivity Multi-channel Quad-conf Igurat Ion Receiver With Digital Slicer
• Manufacturer: Infineon Technologies Corporation

2.4.6.4
Automatic Gain Control (AGC) is necessary mainly because of the limited dynamic range
of the on-chip bandpass filter (BPF). The dynamic range reduces to less than 60dB in
case of minimum BPF bandwidth.
AGC is used to cover the following cases:
1. ASK demodulation at large input signals
2. RSSI reading at large input signals
3. Improve IIP3 performance in either FSK or ASK mode
The 1
bits thus optimizing the overall gain to the application (attenuation of 0dB to -12dB by
means of IFATT0 to IFATT15 in DDC mode; SDC mode has lower IFATT range). This
buffer allows the production spread of external components to be trimmed.
The gain of the 2
Depending on whether the receiver is used in single down conversion or in double down
conversion mode the gain control in the 2
network or in front of the 2
The AGC action is illustrated in the RSSI curve below:
Figure 12
Data Sheet
st
IF buffer (PPFBUF, see
noise x gain
Front- end
Digital Automatic Gain Control Unit (AGC)
Analog RSSI output curve with AGC action ON (blue) vs. OFF (black)
Analog AGC
attack point
Analog AGC
decay point
saturation
saturation
nd
noise floor
Mixer2
Limiter
Analog (blue)
BPF
Max. B W
Min. B W
digital (black )
IF path is set to three different values by means of an AGC algorithm.
RSSI output
Max . FE gain
Min. FE gain
(IFA TT 15)
(IFA TT 0)
Max. B W
Min. B W
&
hysteresis
nd
mixer.
Figure
3) can be fine tuned "manually" by means of 4
margin
29
nd
BPF bypassed
IF path is either after the 2
AGC OFF
AGC ON
Functional Description
Input power
V1.0, 2010-02-19
nd
poly-phase
TDA5225