Introduction
The ADF7021-N is a high-performance, low-power, narrowband transceiver featuring IF filter bandwidths of 9 kHz, 13.5 kHz, and 18.5 kHz, fully compliant with a wide range of global narrowband communications standards, particularly those requiring 12.5 kHz channel spacing.
The ADF7021-N operates in narrowband, license-free ISM bands and licensed bands within the frequency ranges of 80 MHz to 650 MHz and 842 MHz to 916 MHz. The device offers Gaussian and raised cosine transmit data filtering options to improve spectral efficiency in narrowband applications. It is suitable for circuit applications complying with the following standards or regulations: Japan ARIB STD-T67, Europe ETSI EN300220, Korea Short Range Device regulations, China Short Range Device regulations, and North America FCC Part 15, Part 90, and Part 95 regulatory standards. The ADF7021-N requires only a small number of external discrete components to form a complete transceiver, making it ideal for cost-sensitive and space-sensitive applications.
A comprehensive set of on-chip FSK modulation and data filtering options gives users greater flexibility in selecting modulation schemes while meeting stringent spectral efficiency requirements. The ADF7021-N also supports protocols that dynamically switch between 2FSK, 3FSK, and 4FSK to maximize communication range and improve data throughput.
The transmitter incorporates two voltage-controlled oscillators (VCOs) and a low-noise fractional-N PLL with output frequency resolution of <1 ppm. One VCO utilizes an internal LC resonator (421 MHz to 458 MHz, 842 MHz to 916 MHz), while the other uses an external inductor as part of its resonant circuit (80 MHz to 650 MHz). The dual-VCO architecture enables dual-band operation, allowing users to transmit and receive at any frequency supported by the internal inductor VCO or within specific bands supported by the external inductor VCO.
With a fast-frequency-hopping PLL, the ADF7021-N is suitable for frequency hopping spread spectrum (FHSS) systems. Both VCOs operate at twice the fundamental frequency to reduce spurious emissions and frequency pulling.
Transmitter output power is programmable in 63 steps from −16 dBm to +13 dBm, with automatic power ramp control to avoid spectral spurious emissions and assist in meeting regulatory standards. The RF frequency, channel spacing, and modulation of the transceiver can all be programmed via a simple 3-wire interface. The device operates from a 2.3 V to 3.6 V supply and supports a shutdown function.
The receiver employs a low-IF architecture (100 kHz), achieving minimum power consumption and a minimal external component count while avoiding DC offset and flicker noise at low frequencies. The IF filter features a programmable bandwidth of 9 kHz, 13.5 kHz, and 18.5 kHz. The ADF7021-N supports a wide range of programmable features, including receiver linearity, sensitivity, and IF bandwidth, allowing users to make trade-offs between receiver sensitivity, selectivity, and power consumption for specific applications. The receiver also features a patent-pending automatic frequency control (AFC) loop with programmable capture range, enabling the PLL to track frequency errors in the input signal.
Using a patent-pending image rejection (IR) calibration scheme that requires no external RF source, the receiver achieves image rejection performance of 56 dB.
An on-chip ADC provides readback of an integrated temperature sensor, external analog input, battery voltage, and RSSI signals, reducing ADC overhead in certain applications. The temperature sensor achieves an accuracy of ±10°C over the full operating temperature range of −40°C to +85°C. A single-point calibration performed at room temperature with results stored in memory can improve this accuracy.
