Maxim: MAX7032 Wireless Automatic Meter Reader Reference Design

Maxim’s MAX7032 is a crystal-based fractional-N transceiver that can transmit and receive ASK/OOK or FSK data from 300MHz to 450MHz, with data rates up to 33kbps (Manchester encoding) or 66kbps (NRZ encoding). Single-supply+ 2.1V – +3.6V or +4.5V – +5.5V, typical RF sensitivity: ASK is -114dBm, FSK is -110dBm. Mainly used in industrial control, home automation, remote sensing technology, garage access control, local telemetry systems, two-way No keyboard input, smoke alarm and remote control, etc. This article introduces the MAX7032 main features, block diagram, typical application circuit and its bill of materials, as well as the wireless automatic meter reading reference design MTR part circuit diagram and RDR part circuit diagram with the corresponding bill of materials, PCB layout .

The MAX7032 crystal-based, fractional-N transceiver is designed to transmit and receive ASK/OOK or FSK data in the 300MHz to 450MHz frequency range with data rates up to 33kbps (Manchester encoded) or 66kbps (NRZ encoded). This device generates a typical output power of +10dBm into a 50Ω load, and exhibits typical sensitivities of -114dBm for ASK data and -110dBm for FSK data. The MAX7032 features transmit separate and receive pins (PAOUT and LNAIN) and provides an internal RF switch that can be used to connect the transmit and receive pins to a common antenna.

The MAX7032 transmit frequency is generated by a 16-bit, fractional-N, phase-locked loop (PLL), while the receiver’s local oscillator (LO) is generated by an integer-N PLL. This hybrid architecture eliminates the need for separate transmit and receive crystal reference oscillators because the fractional-N PLL allows the transmit frequency to be set within 2kHz of the receive frequency. The 12-bit resolution of the fractional-N PLL allows frequency multiplication of the crystal frequency in steps of fXTAL/4096. Retaining the fixed-N PLL for the receiver avoids the higher current drain requirements of a fractional-N PLL and keeps the receiver current drain as low as possible.

The fractional-N architecture of the MAX7032 transmit PLL allows the transmit FSK signal to be programmed for exact frequency deviations, and completely eliminates the problems associated with oscillator-pulling FSK signal generation. All frequency-generation components are integrated on-chip, and only a crystal, a 10.7MHz IF filter, and a few discrete components are required to implement a complete antenna/digital data solution.

The MAX7032 is available in a small 5mm x 5mm, 32-pin,thin QFN package, and is specified to operate in the automotive -40°C to +125°C temperature range.

MAX7032 main features:

♦ +2.1V to +3.6V or +4.5V to +5.5V Single-Supply Operation

♦ Single Crystal Transceiver

♦ User-Adjustable 300MHz to 450MHz Carrier Frequency

♦ ASK/OOK and FSK Modulation

♦ User-Adjustable FSK Frequency Deviation Through Fractional-N PLL Register

♦ Agile Transmitter Frequency Synthesizer with fXTAL/4096 Carrier-Frequency Spacing

♦ +10dBm Output Power into 50Ω Load

♦ Integrated TX/RX Switch

♦ Integrated Transmit and Receive PLL, VCO, and Loop Filter

♦ > 45dB Image Rejection

♦ Typical RF Sensitivity*

ASK: -114dBm

FSK: -110dBm

♦ Selectable IF Bandwidth with External Filter

♦ RSSI Output with High Dynamic Range

♦ Autopolling Low-Power Management

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♦ Fast-On Startup Feature,

♦ Small 32-Pin, Thin QFN Package

MAX7032 application:

2-Way Remote Keyless Entry

Security Systems

Home Automation

Remote Controls

Remote Sensing

Smoke Alarms

Garage Door Openers

Local Telemetry Systems

Figure 1. MAX7032 block diagram

Figure 2. Typical application circuit diagram of the MAX7032
Figure 2 Typical Application Circuit Bill of Materials (BOM):


Figure 3. Circuit diagram of MTR part (1)

Figure 4. MTR part circuit diagram (2)

Figure 5. Circuit diagram of MTR part (3)

Figure 6. MTR part circuit diagram (4)
MTR part material list:


Figure 7. RDR part circuit diagram (1)

Figure 8. RDR part circuit diagram (2)

Figure 9. RDR part circuit diagram (3)

Figure 10. RDR part circuit diagram (4)

RDR part list of materials:

Figure 11. Wireless Automatic Meter Reading Reference Design PCB Layout
For details, see:
http://datasheets.maxim-ic.com/en/ds/MAX7032.pdf
and
http://pdfserv.maxim-ic.com/en/an/REFD5391.pdf