PR
EL
IMI
NA
RY
SW71122
MLX71122 RF Receiver
Programming Software Manual
39011 71122 01
Page 14 of 21
SW71122-Manual
Rev. 004
Aug/11
5.2.4
2
nd
Mixer Gain
These radio buttons set the MIX2GAIN bit. It specifies the gain of the 2
nd
mixer.
Possible selections are: -2dB, +9dB (default)
5.2.5
Demodulator Gain
These radio buttons control the frequency to voltage conversion gain of the FSK-demodulator:
•
low
12mV/kHz (default)
•
high
14.5mV/kHz
The Automatic Gain Control (AGC) enables the circuit to keep its internal voltage amplitude levels in the
linear operation range of the different front end blocks. By default the gain settings are high to keep the noise
contribution of the active IF-filter as low as possible. If the input signal increases the filter will soon become
nonlinear because the input level is too high. A digital control circuit of the MLX71122 can be used to lower
the gains of the previous blocks to maintain the linear input range of the IF-filter as far as possible. First the
gain of mixer 2 is lowered, then mixer 1 and in the end the LNA gain.
5.2.6
RSSI Gain
The RSSIGAIN setting determines the RSSI gain of the IFA:
•
low
39mV/dB
•
high
51mV/dB (default)
The output voltage range of the RSSI voltage will also be affected by this setting.
5.2.7
Enable AGC
This checkbox enables or disables (default) the AGC feature. Make sure that RSSIGAIN is high to use AGC.
5.2.8
Delay Settings
The AGC circuit uses the RSSIL and RSSIH flags to specify whether the gains have to be increased or
decreased. In order to make the gain switching independent of short signal fluctuations, four delay times are
selectable that specify how long the RSSIL or RSSIH flags have to be set before the gains are changed. The
delays are related to the reference frequency of the IF-filter adjustment circuit f
IFF
. If the reference oscillator
frequency is 10MHz then f
IFF
should be equal to 3MHz.
•
Selectable delays are
0 / f
IFF
(default), 3 / f
IFF
, 15 / f
IFF
, 31 / f
IFF
•
or for 10 MHz RO frequency
0
µ
s (default), 1
µ
s, 5
µ
s, 10.3
µ
s
5.2.9
Delay Mode
These radio buttons specify whether the delay is only applied at gain increase and not at decrease (default),
or for both, increase and decrease.
