MAX7032 データシートの表示（PDF） - Maxim Integrated

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MAX7032

Low-Cost, Crystal-Based, Programmable, ASK/FSK Transceiver with Fractional-N PLL

Maxim Integrated 

Low-Cost, Crystal-Based, Programmable,

ASK/FSK Transceiver with Fractional-N PLL

Pin Description (continued)

PIN

NAME

FUNCTION

High-Voltage Supply Input. For 3V operation, connect HVIN to PAVDD, AVDD, and DVDD. For 5V

27

HVIN

operation, connect only HVIN to 5V. Bypass HVIN to GND with 0.01µF and 220pF capacitors placed

as close as possible to the pin.

28

CS

Serial Interface Active-Low Chip Select

29

DIO

Serial Interface Serial Data Input/Output

30

SCLK Serial Interface Clock Input

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 AC-coupled external reference.

—

EP

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

Detailed Description

The MAX7032 300MHz to 450MHz CMOS transceiver

and a few external components provide a complete

transmit and receive chain from the antenna to the digi-

tal data interface. This device is designed for transmit-

ting and receiving ASK and FSK data. All transmit

frequencies are generated by a fractional-N-based syn-

thesizer, allowing for very fine frequency steps in incre-

ments 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

impedance 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 must be done to optimize

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. The AGC has a hys-

teresis of approximately 4dB. With the AGC function,

the RSSI dynamic range is increased, allowing the

MAX7032 to reliably produce an ASK output for RF

input levels up to 0dBm with a modulation depth of

18dB. AGC is not required and can be disabled in

either ASK or FSK mode. AGC is not necessary for FSK

mode because large received signal levels do not

affect FSK performance.

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