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MAX9947ETE

AISG Integrated Transceiver

Maxim Integrated 

MAX9947

AISG Integrated Transceiver

External Termination and

AC-Coupling to Feeder Cable

The MAX9947 transceiver works in conjunction with an

external 50I termination. The termination is connected

serially between TXOUT and the feeder cable. It acts as

series termination for the transmitting path (data flowing

from TXIN to TXOUT) and acts as parallel termination

when data is being received on RXIN.

The output of the transmitter is biased at 1.5V to maximize

the power-supply rejection ratio and minimize the emis-

sion. It is recommended that the device be AC-coupled to

the feeder cable through either an external RF filter or a

series 100nF capacitor.

Transmission Output Power

The MAX9947 output level at TXOUT can be set by

using two external resistors that connect at the RES

and BIAS pins as shown in the Typical Application

Circuit (Connectivity at the Base) and Typical Application

Circuit (Connectivity at the Tower). The maximum volt-

age at TXOUT is 2.52VP-P. Assuming that the feeder

cable is terminated into a 50Ω impedance, the external

filter is lossless at 2.176MHz, and a series 50Ω termina-

tion is being used as in the Typical Application Circuit

(Connectivity at the Base) and Typical Application Circuit

(Connectivity at the Tower), the output level of 2.52VP-P

corresponds to +6dBm at the feeder cable.

The TXOUT voltage level can be varied according to the

following equations:

VTXOUT (VP-P) = (2.52VP-P x VRES (V))/1.5V

VRES (V) = 1.5V x R2/(R1 + R2)

VTXOUT (VP-P) = 2.52VP-P x R2/(R1 + R2)

Use R1 = 0Ω for maximum voltage level of 2.52VP-P.

The voltage at the RES pin must be between 0.84V and

1.5V. It implies that the minimum voltage level at TXOUT

is approximately 1.41V that corresponds to +1dBm at the

feeder cable. It is recommended that a 1μF capacitor be

connected between the BIAS pin and ground.

To obtain the nominal power level of +3dBm at the feeder

cable as the AISG standard requires, use R1 = 4.1kΩ and

R2 = 10kΩ that provide 1.78VP-P at TXOUT.

The MAX9947 can provide up to 2.52VP-P to compensate

for potential loss within the external filter, cable, connec-

tions, and termination.

Receiver-Input Range and Threshold

The maximum OOK input power at RXIN into the 50Ω

external termination is +5dBm. For a single-tone signal at

2.176MHz, 5dBm corresponds to 1.12VP-P.

The MAX9947 internal threshold is -15dBm (112.4mVP-P)

with ±3dB accuracy in compliance with the AISG standard

specifications. This threshold sets the minimum input sig-

nal level that is recognized as OOK carrier being present

(level logic-low).

Consider a corner case where the OOK signal at 2.176MHz

present at the RXIN pin is at the minimum level of -15dBm

±3dB. To avoid the saturation of the receiver input stage,

any other adjacent carrier with power-up to +5dBm must

be either below 1.1MHz or above 4.5MHz.

External Clock

The MAX9947 integrated AISG transceiver operates

with an external crystal at 4x the 2.176MHz frequency,

or 8.704MHz. The crystal is required to achieve the

±100ppm frequency stability specification of the AISG

standard. A crystal with ±30ppm is recommended along

with two 40pF (±10% tolerance) capacitors connect-

ed to ground as shown in Typical Application Circuit

(Connectivity at the Base) and Typical Application Circuit

(Connectivity at the Tower). The capacitors do not affect

the oscillation frequency.

Multiple MAX9947 devices can share the same crystal

by using the SYNCOUT pin. One device acts as a mas-

ter and provides the 8.704MHz clock signal to the slave

device(s) through such a pin. To configure a device as a

slave, XTAL2 should be connected to ground. The exter-

nal clock coming from the master device feeds the XTAL1

pin of the slave device through a series 10kΩ resistor.

Connect a 1kΩ pullup resistor to VCC from the SYNCOUT

pin of the master device.

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