tda5235 Infineon Technologies Corporation, tda5235 Datasheet - Page 30

• Manufacturer Part Number: tda5235
• Description: Enhanced Sensitivity Double-configuration Receiver With Digital Baseband Processing
• 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 AGC
attack point
Analog AGC
decay point
Analog RSSI output curve with AGC action ON (blue) vs. OFF (black)
saturation
saturation
noise floor
Mixer2
Limiter
nd
Analog (blue)
BPF
Max . B W
Min. B W
digital (black )
RSSI output
IF path is set to three different values by means of an AGC algorithm.
Max. FE gain
Min. FE gain
(IFA TT 15)
(IFA TT 0)
Max . B W
Min. B W
&
hy s teres is
nd
mixer.
Figure
3) can be fine tuned "manually" by means of 4
margin
30
nd
IF path is either after the 2
BPF bypassed
AGC OFF
Functional Description
AGC ON
V1.0, 2010-02-19
nd
Input power
poly-phase
TDA5235