On Microchip AT86RF215 Radios | Wi-fi Pi

2023-07-14 22:01:58

It’s a little uncommon to explain a {hardware} radio on an internet site that focuses on software program radios. However I used to be impressed with the performance and efficiency of AT86RF215 transceivers by Microchip throughout my experiments. I’ve used them for node localization and they are often put to many different good makes use of, together with, …. right here is the shock, …. as software program outlined radios.

By way of a bit programming effort, I/Q samples from the digital frontend will be straight accessed utilizing which you’ll run your personal baseband on a digital sign processor. Though interfacing with an exterior system for I/Q samples supply is just not simple, it is a very highly effective function, amongst others, that this system has to supply.

Should you like experimentation with radios and DSP, then this is perhaps an choice with the next professionals and cons.

Sign conditioning and processing in analog and digital domains is {of professional} grade, versus a lot of the {hardware} and software program employed typically software program outlined radios.
You’ll not run into completely different sorts of widespread latency points.
As talked about earlier than, capturing the I/Q samples from the system is just not simple. It’s achieved by means of a 13-bit I/Q Low Voltage Differential Sign (LVDS) interface that may route the I/Q information on to any exterior processor for utility of DSP methods. See the datasheet for the detailed process.

Beneath is the primary look of the related ATREB-XPRO analysis board with the chip within the middle.

Allow us to go into extra technical particulars.

Introduction

The AT86RF215 is a multi-band radio transceiver for varied sub-1GHz bands and the two.4GHz band that’s compliant to IEEE 802.15.4-2011, IEEE 802.15.4g-2012, and ETSI TS 102 887-1.requirements. The functions embrace sensible metering, sensible lighting, residence vitality gateways, and different industrial and automation Web of Issues (IoT).

It helps the next multi-rate and multi-regional modulation schemes on the bodily layer.

MR-FSK
- Image charges: 50, 100, 150, 200, 300, 400 ksymbol/s
- Price 1/2-FEC: RSC and NRNSC, with and with out interleaving

MR-OFDM
- Choice 1: 100, 200, 400, 800, 1200, 1600, 2400 kb/s
- Choice 2: 50, 100, 200, 400, 600, 800, 1200 kb/s
- Choice 3: 50, 100, 200, 300, 400, 600 kb/s
- Choice 4: 50, 100, 150, 200, 300 kb/s

MR-OQPSK
- 100kchip/s with 6.25, 12.5, 25, 50 kb/s
- 200kchip/s with 12.5, 25*, 50, 100 kb/s
- 1000kchip/s with 31.25, 125, 250, 500 kb/s
- 2000kchip/s with 31.25, 125, 250, 500, 1000 kb/s

Each transceivers, in sub-GHz and a pair of.4 GHz bands, can function concurrently as every of them incorporates its personal I/Q information interface and baseband engine, thus forming two unbiased radio programs. The determine under reveals the block diagram of the chip (picture courtesy of Microchip).

From a DSP perspective, the next options of Microchip AT86RF215 are notably attention-grabbing.

Tx Frontend

Analog

So far as the Tx analog frontend is anxious, the transmitter is predicated on a direct upconversion architecture. After the digital to analog converter (DAC) the IQ alerts are handed by means of an analog 2nd order low-pass filters which covers a cut-off frequency vary from 80 kHz to 1000 kHz with uniform logarithmic stepping.

Digital

In keeping with the datasheet, the Transmitter Digital Frontend (TX_DFE) performs discrete time sample rate conversion of the complicated baseband sign based mostly on a zero-Intermediate Frequency (zero-IF) structure. The I/Q information sampling frequency $f_s$ is configured in line with the relation
[
f_s = frac{4}{SR}~ text{MHz}
]

the place SR is outlined by a register named as TXDFE.SR. The sign processing movement is depicted within the determine under. The block PRE_FLT filters the baseband sign on the sampling frequency $f_s$.

To chill out the interpolation complexity of the baseband processor that suppresses the undesirable photographs, a choice of appropriate normalized cut-off frequencies $f_{textual content{lower}}$ (TXDFE.RCUT) is obtainable. For $f_{lower}$ equal to 1, this block is bypassed, decreasing the group delay and latency. Upsampling from $f_s$ to 4MHz is completed by the block UP_SRC(1:SR) that employs a linear section FIR interpolation filter with normalized cut-off frequency 1/SR. Lastly, the block UP_SRC(1:8) upsamples to the DAC sampling frequency of 32MHz by using three phases of linear section FIR filters with normalized cut-off frequency $1/2$.

Rx Frontend

Analog

As drawn within the determine under, the primary block within the Rx frontend is a Low Noise Amplifier (LNA). Subsequent, the obtained sign is down-converted to a low intermediate frequency (IF). This mixture of a variable IF together with variable band-pass filters supplies flexibility with respect to channel choice at completely different channel spacings.

The band-pass filter frequency response follows a 2nd order Butterworth attribute that gives adjoining channel sign attenuation earlier than the analog to digital conversion. Versus the Tx frontend, the vary from 160kHz to 2000kHz is roofed with uniform logarithmic stepping.

Digital

As depicted within the above determine, the first duties completed by the Rx digital frontend are as follows.

Sample rate conversion of the complicated baseband sign
Implementation of Computerized Achieve Management (AGC) that maintains a predetermined sign amplitude at its output, regardless of variations within the sign amplitude on the enter
Estimation of Received Signal Strength Indicator (RSSI) that may be a crude measure of obtained sign energy

The ADC supplies the uncooked information of the complicated low-IF baseband sign at a sampling frequency of 32MHz. Within the block DOWN_SRC(1:8), the uncooked information is downsampled to the sampling frequency of 4MHz and transformed to zero-IF by the DOWN_MIX block. Relying on the configuration register RXDFE.SR, the sign is additional down-sampled by the block DOWN_SRC(1:SR) to the goal obtain sampling frequency given as
[
f_s = frac{4}{SR}~ text{MHz}
]

That is completed by means of a a linear section FIR decimation filter with normalized cut-off frequency 1/SR. To cope with adjoining channel interference, the baseband sign will be additional filtered by the block POST_FLT by which a choice of appropriate normalized cut-off frequencies $f_{textual content{lower}}$ is obtainable. Right here, you may also benefit from the description of Cascade Integrator Comb (CIC) filters and the way they accomplish the duty of pattern fee conversion with minimal sources in digital frontends of transmitters and receivers.

Section Measurement Unit (PMU)

For me, that is essentially the most attention-grabbing function of this system which is sort of unusual in any class of radio receivers. The Section Measurement Unit (PMU) screens and information the sign section together with another parameters on the output of the Rx frontend proven within the above determine. That is carried out at a continuing PMU interval of 8 $mu$s.

Within the above determine, allow us to denote the complicated sign on the frontend output I_DATA and Q_DATA as
[
x = x_i + jx_q
]

Then, the datasheet reveals the next expressions within the output registers.

This PMU unit has been extensively utilized by the researchers in academia and business for RF localization based on carrier phases. Lastly, for functions requiring timing markers, every baseband core additionally incorporates a Timestamp Counter module with a 32-bit counter.

Conclusion

These AT86Rf215 transceivers had been developed by ATMEL that was later acquired by Microchip. The product is sort of helpful for radio experimentation in communication and localization with a variety of configurable blocks. Moreover, the section measurements offered by the PMU registers for exterior use usually are not a typical providing in wi-fi business. In my view, these transceivers match fairly properly in the course of the spectrum between {hardware} and software program radios.