AS3900 datasheet(14/59 Pages) AMSCO

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AS3900

Data Sheet - Detail ed Description

8 Detailed Description

The AS3900 transceiver is an integrated solution of one receiver and one transmitter capable of supporting a bidirectional communication

between one Master and up to eight Clients via the 27MHz ISM band. The AS3900 is designed to operate with a single 2.2V to 3.6V supply and

consumes less than 3.8mA in receive mode and 7.6mA in transmit mode (10dBm). The device is even functional down to a supply voltage of

2.0V and has a built in battery level detector, that level can be read via the SDI interface.

The AS3900 provides an adjustable data rate of 26.5 kbps up to 212kbps and transmits an adjustable (via external matching circuitry) output

power of maximal 10dBm. The transmission is done through a power amplifier that sends a Miller coded FSK modulated signal. A I/Q up mixer

generates the modulated RF-signal based on the carrier of 27.12MHz. The deviation of the frequency shift can be set to ±106kHz or to ±53kHz

in order to limit the allocated bandwidth in the ISM band. An integrated low pass filter cuts off additional interference frequencies.

The analog outputs of the PA can be programmed as single ended or fully differentially, which doubles the transmitter output voltage level. In

addition the output impedance of the PA can be selected between 25Ω and 12.5Ω. The output power is mainly determined by the applied output

impedance of the antenna and the matching network.

The AS3900 features a zero-IF receiver. The receiver consists of a differential low noise amplifier (LNA) that amplifies the incoming RF signal.

The actual received signal strength (RSSI) is measured and converted to a digital value that can be read via the serial data interface. Afterwards

the incoming signal is down converted (I and Q) to the base band by the mixer. The I/Q signal is filtered and fed to the demodulator.

Furthermore the receiver consists of a Wakeup LNA. The amplified wakeup signal is demodulated and correlated with the OOK-pattern. This

functionality guarantees very low power requirements ideal for battery-operated applications. The device is set to STANDBY mode and scans

periodically for the ON OFF keying signal (OOK) with the Wakeup receiver, which only consumes an average current of 2.5µA. Once detected

the AS3900 enters the normal RX mode.

A key feature of the AS3900 is the integrated Link Manager. The Link Manager controls all issues regarding the low level communication. It

manages the link parameters and the timings in order to set-up and to maintain up to 8 communication links simultaneously. The link manager

uses the integrated timers and the pseudorandom binary sequence (PRBS), to run the low level actions automatically. For reliable data

transmission a 16 bit CRC block is integrated. Furthermore the transmitted data is Miller coded. Two crystal oscillators must be connected in

order to generate the carrier of 27.12MHz and the time base for the timers (RTC), which is 32.768 kHz. The clock source for the MCU_CLK can

be converted from the 32.768 kHz real-time clock or from the 27.12MHz carrier. The 4-wire SDI (Serial Data Interface) is used for configuration

of the AS3900 and to serve the link manager. The SDI interface allows the access to the MAIN register as well as to the SHADOW register. The

data for the RF transmission is saved into the data buffer at the Clients and can be collected at the Master that is again saved in the data buffer

in the MAIN register. A simplified block diagram of the AS3900 is shown in Figure 9.

Figure 9. Block Diagram of Low Power Star Network Transceiver AS3900

LNA

RSSI

Wakeup

LNA

OOK

Demodulation

Correlation

CRC

OTP

Timers

PRBS

Data Buffer

MAIN Register

SHADOW

RF1OUT

RF2OUT

RF1IN

RF2IN

SEN

SCLK

SDATAO

SDATAI

IRQ

POR

Battery Level

Detector

RTC

X32_IN X32_OUT

XREF

X27_IN X27_OUT

MCU_CLK

VDD_OTP VSS_OTP

VDDRF GND

VDD

GND

AS3900

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