MCP2030 datasheet(39/66 Pages) MICROCHIP

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DS21981A-page 39

MCP2030

TABLE 5-2:

INPUT SENSITIVITY VS. MODULATED SIGNAL STRENGTH SETTING (AGCSIG <7>)

5.17

Input Channels (Enable/Disable)

Each channel can be individually enabled or disabled

by programming bits in Configuration Register 0<3:1>

(Register 5-1).

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.

5.18

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

initialization 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:

During the AGC initialization time (TAGC), the

AGC time constant is fast, allowing a reasonably

short acquisition time of the continuous input

signal.

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.

5.19

AGC Preserve

The AGC preserve feature is used to preserve the AGC

value during the AGC initialization time (TAGC) and

apply the value to the data slicing circuit for the follow-

ing 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 varia-

tions at a given time period. This feature is enabled

when the device receives an AGC Preserve On com-

mand and disabled if it receives an AGC Preserve Off

command. Once the AGC Preserve On command is

received, the device acquires a new AGC value during

each AGC initialization 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 5.31.2.5 “AGC Preserve On

Command” and Section 5.31.2.6 “AGC Preserve Off

Command” for AGC Preserve commands).

AGCSIG<7>

(Config. Register 5)

Description

Input

Sensitivity

(Typical)

Option Disabled – Detect any input signal level (demodulated data and

carrier clock).

3.0 mVPP

Option Enabled – No output until AGC Status = 1 (i.e., VPEAK ≈ 20 mVPP)

(demodulated data and carrier clock).

• Provides the best signal to noise ratio.

20 mVPP

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