RF96 datasheet(80/121 Pages) HOPE

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Page 80

RF96/97/98

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WIRELESS & SENSING

PRELIMINARY

DATASHEET

5.4.4. Over Current Protection

The power amplifiers of RF96/97/98 are protected against current over supply in adverse RF load conditions by the over

current protection block. This has the added benefit of protecting battery chemistries with limited peak current capability

and minimising worst case PA consumption in battery life calculation. The current limiter value is controlled by the OcpTrim

bits in RegOcp, and is calculated according to the following formulae:

Table 81 Trimming of the OCP Current

OcpTrim

IMAX

Imax Formula

0 to 15

45 to 120 mA

45 + 5*OcpTrim [mA]

16 to 27

130 to 240 mA

-30 + 10*OcpTrim [mA]

27+

240 mA

Note Imax sets a limit on the current drain of the Power Amplifier only, hence the maximum current drain of the

RF96/

77/78 is equal to Imax + IFS.

5.5. Receiver Description

5.5.1. Overview

The RF96/97/98 features a digital receiver with the analog to digital conversion process being performed directly

following the LNA-Mixers block. In addition to the LoRaTM modulation scheme the low-IF receiver is able to demodulate

ASK, OOK, (G)FSK and (G)MSK modulation. All filtering, demodulation, gain control, synchronization and packet handling

is performed digitally allowing a high degree of programmable flexibility. The receiver also has automatic gain calibration,

this improves the precision of RSSI measurement and enhances image rejection.

5.5.2. Receiver Enabled and Receiver Active States

In the receiver operating mode two states of functionality are defined. Upon initial transition to receiver operating mode the

receiver is in the

„receiver-enabled‟ state. In this state the receiver awaits for either the user defined valid preamble or RSSI

detection criterion to be fulfilled. Once met the receiver enters

„receiver-active‟ state. In this second state the received

signal is processed by the packet engine and top level sequencer. For a complete description of the digital functions of the

RF96/97/98 receiver please see Section 4 of the datasheet.

5.5.3. Automatic Gain Control In FSK/OOK Mode

The AGC feature allows receiver to handle a wide Rx input dynamic range from the sensitivity level up to maximum input

level of 0dBm or more, whilst optimizing the system linearity.

The following table shows typical NF and IIP3 performances for the RF96/97/98 LNA gains available.

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