MAX7030 Ver la hoja de datos (PDF) - Maxim Integrated

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MAX7030

Low-Cost, 315MHz, 345MHz, and 433.92MHz ASK Transceiver with Fractional-N PLL

Maxim Integrated 

Low-Cost, 315MHz, 345MHz, and 433.92MHz

ASK Transceiver with Fractional-N PLL

Pin Description (continued)

PIN

NAME

FUNCTION

28

AGC2 AGC Enable/Dwell Time Control 2 (MSB). See Table 1. Bypass to GND with a 10pF capacitor.

29

AGC1 AGC Enable/Dwell Time Control 1. See Table 1. Bypass to GND with a 10pF capacitor.

30

AGC0 AGC Enable/Dwell Time Control 0 (LSB). See Table 1. Bypass to GND with a 10pF capacitor.

31

XTAL1 Crystal Input 1. Bypass to GND if XTAL2 is driven by an AC-coupled external reference.

32

XTAL2 Crystal Input 2. XTAL2 can be driven from an external AC-coupled reference.

—

EP

Exposed Pad. Solder evenly to the board’s ground plane for proper operation.

Detailed Description

The MAX7030 315MHz, 345MHz, and 433.92MHz

CMOS transceiver and a few external components pro-

vide a complete transmit and receive chain from the

antenna to the digital data interface. This device is

designed for transmitting and receiving ASK data. All

transmit frequencies are generated by a fractional-N-

based synthesizer, allowing for very fine frequency

steps in increments of fXTAL/4096. The receive LO is

generated by a traditional integer-N-based synthesizer.

Depending on component selection, data rates as high

as 33kbps (Manchester encoded) or 66kbps (NRZ

encoded) can be achieved.

Receiver

Low-Noise Amplifier (LNA)

The LNA is a cascode amplifier with off-chip inductive

degeneration that achieves approximately 30dB of volt-

age gain that is dependent on both the antenna-match-

ing network at the LNA input and the LC tank network

between the LNA output and the mixer inputs.

The off-chip inductive degeneration is achieved by

connecting an inductor from LNASRC to GND. This

inductor sets the real part of the input impedance at

LNAIN, allowing for a more flexible match for low-input

impedances such as a PCB trace antenna. A nominal

value for this inductor with a 50Ω input impedance is

12nH at 315MHz and 10nH at 434MHz, but the induc-

tance is affected by PCB trace length. LNASRC can be

shorted to ground to increase sensitivity by approxi-

mately 1dB, but the input match must then be reopti-

mized.

The LC tank filter connected to LNAOUT consists of L5

and C9 (see the Typical Application Circuit). Select L5

and C9 to resonate at the desired RF input frequency.

The resonant frequency is given by:

f=

1

2π LTOTAL × CTOTAL

where LTOTAL = L5 + LPARASITICS and CTOTAL = C9 +

CPARASITICS.

LPARASITICS and CPARASITICS include inductance and

capacitance of the PCB traces, package pins, mixer-

input impedance, LNA-output impedance, etc. These

parasitics at high frequencies cannot be ignored, and

can have a dramatic effect on the tank filter center fre-

quency. Lab experimentation should be done to opti-

mize the center frequency of the tank. The total

parasitic capacitance is generally between 5pF and

7pF.

Automatic Gain Control (AGC)

When the AGC is enabled, it monitors the RSSI output.

When the RSSI output reaches 1.28V, which corre-

sponds to an RF input level of approximately -55dBm,

the AGC switches on the LNA gain-reduction attenua-

tor. The attenuator reduces the LNA gain by 36dB,

thereby reducing the RSSI output by about 540mV to

740mV. The LNA resumes high-gain mode when the

RSSI output level drops back below 680mV (approxi-

mately -59dBm at the RF input) for a programmable

interval called the AGC dwell time (see Table 1). The

AGC has a hysteresis of approximately 4dB. With the

AGC function, the RSSI dynamic range is increased,

allowing the MAX7030 to reliably produce an ASK out-

put for RF input levels up to 0dBm with a modulation

depth of 18dB. AGC is not required and can be dis-

abled (see Table 1).

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