PIC16F636-I Datasheet, PDF (108/234 Pages) Microchip Technology – 8/14-Pin, Flash-Based 8-Bit CMOS Microcontrollers with nanoWatt Technology

PIC12F635/PIC16F636/639
TABLE 11-2: INPUT SENSITIVITY VS. MODULATED SIGNAL STRENGTH SETTING (AGCSIG <7>)
AGCSIG<7>
(Config. Register 5)
Description
Input
Sensitivity
(Typical)
0
Disabled – the AFE passes signal of any amplitude level it is capable of
3.0 mVPP
detecting (demodulated data and carrier clock).
1
Enabled – No output until AGC Status = 1 (i.e., VPEAK ≈ 20 mVPP)
(demodulated data and carrier clock).
20 mVPP
• Provides the best signal to noise ratio.
11.17 Input Channels (Enable/Disable)
Each channel can be individually enabled or disabled
by programming bits in Configuration Register 0<3:1>
(Register 11-1).
The purpose of having an option to disable a particular
channel is to minimize current draw by powering down
as much circuitry as possible, if the channel is not
needed for operation. The exact circuits disabled when
an input is disabled are amplifiers, detector, full-wave
rectifier, data slicer, and modulation FET. However, the
RF input limiter remains active to protect the silicon
from excessive antenna input voltages.
11.18 AGC Amplifier
The circuit automatically amplifies input signal voltage
levels to an acceptable level for the data slicer. Fast
attack and slow release by nature, the AGC tracks the
carrier signal level and not the modulated data bits.
The AGC inherently tracks the strongest of the three
antenna input signals. The AGC requires an AGC
stabilization time (TAGC).
The AGC will attempt to regulate a channel’s peak
signal voltage into the data slicer to a desired regulated
AGC voltage – reducing the input path’s gain as the
signal level attempts to increase above regulated AGC
voltage, and allowing full amplification on signal levels
below the regulated AGC voltage.
The AGC has two modes of operation:
1. During the AGC settling time (TAGC), the AGC
time constant is fast, allowing a reasonably short
acquisition time of the continuous input signal.
2. After TAGC, the AGC switches to a slower time
constant for data slicing.
Also, the AGC is frozen when the input signal envelope
is low. The AGC tracks only high envelope levels.
11.19 AGC Preserve
The AGC preserve feature allows the AFE to preserve
the AGC value during the AGC settling time (TAGC) and
apply the value to the data slicing circuit for the following
data streams instead of using a new tracking value. This
feature is useful to demodulate the input signal correctly
when the input has random amplitude variations at a
given time period. This feature is enabled when the AFE
receives an AGC Preserve On command and disabled
if it receives an AGC Preserve Off command. Once the
AGC Preserve On command is received, the AFE
acquires a new AGC value during each AGC settling
time and preserves the value until a Soft Reset or an
AGC Preserve Off command is issued. Therefore, it
does not need to issue another AGC Preserve On
command. An AGC Preserve Off command is needed to
disable the AGC preserve feature (see
Section 11.32.2.5 “AGC Preserve On Command”
and Section 11.32.2.6 “AGC Preserve Off
Command” for AGC Preserve commands).
DS41232D-page 106
© 2007 Microchip Technology Inc.