PIC12F635/PIC16F636/639
TABLE 11-3: SETTING FOR MINIMUM
MODULATION DEPTH
11.20 Soft Reset
The AFE issues a Soft Reset in the following events:
REQUIREMENT
MODMIN Bits
(Config. Register 5)
a) After Power-on Reset (POR),
b) After Inactivity timer time-out,
c) If an “Abort” occurs,
Modulation Depth
Bit 6
Bit 5
d) After receiving SPI Soft Reset command.
0
0
1
1
0
1
0
1
50% (default)
75%
The “Abort” occurs if there is no positive signal
detected at the end of the AGC stabilization period
(TAGC). The Soft Reset initializes internal circuits and
brings the AFE into a low current Standby mode
operation. The internal circuits that are initialized by the
Soft Reset include:
25%
12%
• Output Enable Filter
• AGC circuits
• Demodulator
• 32 kHz Internal Oscillator
The Soft Reset has no effect on the Configuration register
setup, except for some of the AFE Status Register 7 bits.
(Register 11-8).
The circuit initialization takes one internal clock cycle
(1/32 kHz = 31.25 μs). During the initialization, the
modulation transistors between each input and
LCCOM pins are turned-on to discharge any inter-
nal/external parasitic charges. The modulation transis-
tors are turned-off immediately after the initialization
time.
The Soft Reset is executed in Active mode only. It is not
valid in Standby mode.
11.21 Minimum Modulation Depth
Requirement for Input Signal
The AFE demodulates the modulated input signal if the
modulation depth of the input signal is greater than the
minimum requirement that is programmed in the AFE
Configuration Register 5 (Register 11-6). Figure 11-7
shows the definition of the modulation depth and
examples. MODMIN<6:5> of the Configuration Register
5 offer four options. They are 75%, 50%, 25% and 12%,
with a default setting of 50%.
The purpose of this feature is to enhance the
demodulation integrity of the input signal. The 12%
setting is the best choice for the input signal with weak
modulation depth, which is typically observed near the
high-voltage base station antenna and also at
far-distance from the base station antenna. It gives the
best demodulation sensitivity, but is very susceptible to
noise spikes that can result in a bit detection error. The
75% setting can reduce the bit errors caused by noise,
but gives the least demodulation sensitivity. See
Table 11-3 for minimum modulation depth requirement
settings.
© 2007 Microchip Technology Inc.
DS41232D-page 107
MICROCHIP [ MICROCHIP ]
