This version is outdated by a newer approved version.
This version (11 Feb 2016 21:08) was approved by Lars-Peter Clausen.The Previously approved version (22 Jan 2015 13:57) is available.
This version (11 Feb 2016 21:08) was approved by Lars-Peter Clausen.The Previously approved version (22 Jan 2015 13:57) is available.This is an old revision of the document!
Table of Contents
AD6676 Wideband IF Receiver Subsystem Linux device driver
The AD6676 is a highly integrated IF subsystem that can digitize radio frequency (RF) bands up to 160 MHz in width centered on an intermediate frequency (IF) of 70 MHz to 450 MHz.
Supported Devices
Reference Circuits
Evaluation Boards
Description
This is a Linux industrial I/O (IIO) subsystem driver, targeting RF Transceivers. The industrial I/O subsystem provides a unified framework for drivers for many different types of converters and sensors using a number of different physical interfaces (i2c, spi, etc). See IIO for more information.
Source Code
Status
Files
| Function | File |
|---|---|
| driver | drivers/iio/adc/ad6676.c |
| include | drivers/iio/adc/ad6676.h |
Related Device Drivers
| Function | File |
|---|---|
| driver | drivers/iio/adc/cf_axi_adc_core.c |
| driver | drivers/iio/adc/cf_axi_adc_ring_stream.c |
| include | drivers/iio/adc/cf_axi_adc.h |
Example Linux Device-Tree Initialization
The AD6676 driver is a spi-bus driver and can currently only be instantiated via device tree.
Required devicetree properties:
- compatible: Should always be “ad6676”
- reg: SPI slave select number
| Function | File |
|---|---|
| FMCOMMS2/3 Device Tree | zynq-zc706-adv7511-ad6676-fmc.dts |
Device Driver Customization
| Devicetree Property | Description |
|---|---|
| adi,adc-frequency-hz | Initial ADC frequency in Hz |
| adi,adc-frequency-fixed-enable | Prevents ADC frequency changes after initial setup |
| adi,use-external-clk-enable | Use external CLK |
| adi,decimation | Initial decimation rate [12, 16, 24, 32] |
| adi,intermediate-frequency-hz | Initial IF in Hz |
| adi,intermediate-frequency-min-hz | Allowed minimum IF in Hz |
| adi,intermediate-frequency-max-hz | Allowed maximum IF in Hz |
| adi,bandwidth-hz | Initial bandwidth in Hz |
| adi,bandwidth-margin-low-mhz | Initial bandwidth margin low in Hz |
| adi,bandwidth-margin-high-mhz | Initial bandwidth margin high in Hz |
| adi,bandwidth-margin-if-mhz | Initial bandwidth margin IF in Hz |
| adi,external-inductance-l-nh | The inductance of the external inductors in nH |
| adi,idac1-fullscale-adjust | Initial IDAC_FS [64..16] |
| adi,shuffler-control | Initial shuffler control setting |
| adi,shuffler-thresh | Initial shuffler threshold |
| adi,jesd-scrambling-enable | Enables JESD scrambling |
| adi,jesd-use-lvds-syncb-enable | Use LVDS SYNCB |
| adi,jesd-powerdown-sysref-enable | Powerdown SYSREF |
| adi,jesd-l-lanes | Number of JESD lanes |
| adi,jesd-f-frames-per-multiframe | Number of frames per multiframe |
| adi,spi-3wire-enable | Enables SPI 3-WIRE mode |
Enabling Linux driver support
Configure kernel with “make menuconfig” (alternatively use “make xconfig” or “make qconfig”)
The AD6676 driver depends on CONFIG_SPI
Adding Linux driver support
Configure kernel with “make menuconfig” (alternatively use “make xconfig” or “make qconfig”)
Linux Kernel Configuration Device Drivers ---> <*> Industrial I/O support ---> --- Industrial I/O support -*- Enable ring buffer support within IIO -*- Industrial I/O lock free software ring -*- Enable triggered sampling support *** Analog to digital converters *** [--snip--] <*> Analog Devices AD9467 AD9643 High-Speed AXI ADC driver [--snip--]
Hardware configuration
Driver testing / API
Each and every IIO device, typically a hardware chip, has a device folder under /sys/bus/iio/devices/iio:deviceX. Where X is the IIO index of the device. Under every of these directory folders reside a set of files, depending on the characteristics and features of the hardware device in question. These files are consistently generalized and documented in the IIO ABI documentation. In order to determine which IIO deviceX corresponds to which hardware device, the user can read the name file /sys/bus/iio/devices/iio:deviceX/name. In case the sequence in which the iio device drivers are loaded/registered is constant, the numbering is constant and may be known in advance.
TIP: An example program which uses the interface can be found here:
This specifies any shell prompt running on the target
root:/> cd /sys/bus/iio/devices/ root:/sys/bus/iio/devices> ls iio:device0 iio:device1 root:/sys/bus/iio/devices> cd iio:device1 root:/sys/bus/iio/devices/iio:device1# ls -l drwxr-xr-x 5 root root 0 Jan 22 08:19 . drwxr-xr-x 4 root root 0 Jan 22 08:19 .. drwxr-xr-x 2 root root 0 Jan 22 08:19 buffer -r--r--r-- 1 root root 4096 Jan 22 08:19 dev -rw-r--r-- 1 root root 4096 Jan 22 08:19 in_voltage_adc_frequency -rw-r--r-- 1 root root 4096 Jan 22 08:19 in_voltage_bandwidth -rw-r--r-- 1 root root 4096 Jan 22 08:19 in_voltage_bw_margin_high -rw-r--r-- 1 root root 4096 Jan 22 08:19 in_voltage_bw_margin_if -rw-r--r-- 1 root root 4096 Jan 22 08:19 in_voltage_bw_margin_low -rw-r--r-- 1 root root 4096 Jan 22 08:19 in_voltage_hardwaregain -rw-r--r-- 1 root root 4096 Jan 22 08:19 in_voltage_intermediate_frequency -rw-r--r-- 1 root root 4096 Jan 22 08:19 in_voltage_sampling_frequency -rw-r--r-- 1 root root 4096 Jan 22 08:19 in_voltage_scale -rw-r--r-- 1 root root 4096 Jan 22 08:19 in_voltage_shuffler_control -r--r--r-- 1 root root 4096 Jan 22 08:19 in_voltage_shuffler_control_available -rw-r--r-- 1 root root 4096 Jan 22 08:19 in_voltage_shuffler_thresh -r--r--r-- 1 root root 4096 Jan 22 08:19 in_voltage_shuffler_thresh_available -rw-r--r-- 1 root root 4096 Jan 22 08:19 in_voltage_test_mode -r--r--r-- 1 root root 4096 Jan 22 08:19 in_voltage_test_mode_available -r--r--r-- 1 root root 4096 Jan 22 08:19 name drwxr-xr-x 2 root root 0 Jan 22 08:19 power drwxr-xr-x 2 root root 0 Jan 22 08:19 scan_elements lrwxrwxrwx 1 root root 0 Jan 22 08:19 subsystem -> ../../../../../bus/iio -rw-r--r-- 1 root root 4096 Jan 22 08:19 uevent root:/sys/bus/iio/devices/iio:device1#
Show device name
This specifies any shell prompt running on the target
root:/sys/bus/iio/devices/iio:device1> cat name axi-ad6676-hpc
ADC frequency FADC (in_voltage_adc_frequency)
The clock frequency of the ADC. Maximizing the clock frequency is helpful when the IF or bandwidth are high. A lower clock frequency reduces power consumption and is appropriate for low IFs and narrow bandwidths.
Range using external synthesizer [2.0,3.2] GHz in Hz Range using internal synthesizer [2.925,3.2] GHz in Hz
This specifies any shell prompt running on the target
root@analog:/sys/bus/iio/devices/iio:device1# cat in_voltage_adc_frequency 3200000000 root@analog:/sys/bus/iio/devices/iio:device1# echo 3000000000 > in_voltage_adc_frequency -bash: echo: write error: Invalid argument
TIP: If writing this attribute returns “Invalid argument” (-EINVAL) this means that the underlying HDL or Hardware's JESD Core and Gigabit Transceiver (GT) doesn't support changing the JESD Lane Rate.
Complex IQ Data Rate (in_voltage_sampling_frequency)
The complex (I/Q) data rate in SPS. The AD6676 supports decimation factors (DFs) of 12, 16, 24 and 32. The complex (I/Q) data rate at the JESD204B outputs is FADC / DF.
In case the underlying HDL or Hardware's JESD Core and Gigabit Transceiver (GT) support arbitrary JESD Lane Rates. This attribute can be writable. And it will select the appropriate AD6676 supported DFs.
This specifies any shell prompt running on the target
root@analog:/sys/bus/iio/devices/iio:device1# cat in_voltage_sampling_frequency 200000000
IF intermediate frequency (in_voltage_intermediate_frequency)
The IF (intermediate frequency) to which the ADC is tuned. The AD6676 supports IFs from 70 to 450 MHz provided the external inductors are chosen appropriately. Since the AD6676-EBZ by default includes a pair of 19-nH inductors soldered to the evaluation board, the IF range allowed is less than the full range supported by the AD6676.
TIP:
Please see paragraph Lext Selection in the datasheet:
Maximum External Inductor Value as a Function of IF Frequency
The min/max values the device driver accepts can be set via following devicetree attributes:
adi,intermediate-frequency-min-hz = <150000000>; adi,intermediate-frequency-max-hz = <450000000>;
Since the tuning accuracy is finite - reading back this value allows the user to determine the offset.
This specifies any shell prompt running on the target
root@analog:/sys/bus/iio/devices/iio:device1# echo 200000000 > in_voltage_intermediate_frequency root@analog:/sys/bus/iio/devices/iio:device1# cat in_voltage_intermediate_frequency 200000000 root@analog:/sys/bus/iio/devices/iio:device1# echo 199000000 > in_voltage_intermediate_frequency root@analog:/sys/bus/iio/devices/iio:device1# cat in_voltage_intermediate_frequency 199218750
Bandwidth (in_voltage_bandwidth)
The bandwidth of the ADC. Since the AD6676 uses delta-sigma technology, the available bandwidth is a relatively small fraction of the ADC clock rate and the AD6676 achieves the lowest noise and distortion when the bandwidth is small.
The allowed range is between [0.005,0.05]*FADC in Hz
This specifies any shell prompt running on the target
root@analog:/sys/bus/iio/devices/iio:device1# echo 100000000 > in_voltage_bandwidth root@analog:/sys/bus/iio/devices/iio:device1# cat in_voltage_bandwidth 100000000
Bandwidth Margins (in_voltage_bw_margin_[low|high])
Lower (in_voltage_bw_margin_low) and upper (in_voltage_bw_margin_high) bandwidth margins for the noise-shaping profile of the ADC.
Typical values are 5 MHz, but the user may want to increase these margins in wideband operation in order to optimize the noise profile of the ADC.
Typical range [0,30] MHz in MHz
This specifies any shell prompt running on the target
root@analog:/sys/bus/iio/devices/iio:device1# echo 5 > in_voltage_bw_margin_low root@analog:/sys/bus/iio/devices/iio:device1# cat in_voltage_bw_margin_low 5
Bandwidth Margin IF (in_voltage_bw_margin_if)
Displacement of the resonance frequency (F1Shift) of the first resonator within the ADC from band-center. Typically 0 is appropriate, but in the widest bandwidth modes positive shifts can be used to reduce the noise density near the upper edge of the passband.
Typical range [-30,30] MHz in MHz
This specifies any shell prompt running on the target
root@analog:/sys/bus/iio/devices/iio:device1# echo -1 > in_voltage_bw_margin_if root@analog:/sys/bus/iio/devices/iio:device1# cat in_voltage_bw_margin_if -1
Full-Scale (in_voltage_scale)
One of the convenient features of the AD6676 is that the full-scale of its ADC is relatively small and adjustable over a 12-dB range [1.00 .. 0.25] The dynamic range of the ADC is highest at the maximum full-scale setting but the noise figure of the system is lowest at the minimum full-scale setting.
Writing a value of 0.5 to this device attribute lowers the PIN_0dBFS by 6 dB. Likewise writing a value of 0.25 to this device attribute lowers the PIN_0dBFS by 12 dB.
This specifies any shell prompt running on the target
root@analog:/sys/bus/iio/devices/iio:device1# cat in_voltage_scale 1.000000 root@analog:/sys/bus/iio/devices/iio:device1# echo 0.25 > in_voltage_scale root@analog:/sys/bus/iio/devices/iio:device1# cat in_voltage_scale 0.250000
Attenuation Control (in_voltage_hardwaregain)
The AD6676 contains a 50-ohm input attenuator programmable in 1-dB steps. Use this device attribute to set the attenuator's attenuation. The dynamic range of the system increases somewhat with moderate attenuation settings of 6-12 dB, at the expense of an increased noise figure.
The range is from 0 to -27.00 dB in 1dB steps. The nomenclature used here is gain instead of attenuation, so all values are expressed negative.
This specifies any shell prompt running on the target
root@analog:/sys/bus/iio/devices/iio:device1# echo -10.00 > in_voltage_hardwaregain root@analog:/sys/bus/iio/devices/iio:device1# cat in_voltage_hardwaregain -10.000000 dB
Shuffle Control (in_voltage_shuffler_control)
The AD6676 includes dynamic reordering of the comparators within the ADC in order to break up the spurious tones and distortion products associated with a fixed ordering. The Shuffle Control device attribute allows the user to experiment with different shuffling rates. The fadc option (Shuffle every 1) reorders the comparators on every clock cycle with 50% probability. This shuffle scheme is able to randomize deterministic spurs but tends to increase the noise density and creates FADC/32 “shuffle humps” in the output spectrum. Similarly, the fadc/2 fadc/3 fadc/4 (Shuffle every 2,3,4) options reorder the comparators every n clock cycles with 50% probability. Using a high value of n decreases the noise degradation at the expense of less effective randomization and FADC/(32*n) shuffle humps that are closer to the main carrier. Fast shuffling can be disabled by selecting the disable option.
This specifies any shell prompt running on the target
root@analog:/sys/bus/iio/devices/iio:device1# cat in_voltage_shuffler_control_available disable fadc fadc/2 fadc/3 fadc/4 root@analog:/sys/bus/iio/devices/iio:device1# cat in_voltage_shuffler_control fadc root@analog:/sys/bus/iio/devices/iio:device1# echo disable > in_voltage_shuffler_control root@analog:/sys/bus/iio/devices/iio:device1# cat in_voltage_shuffler_control disable
Shuffle Threshold (in_voltage_shuffler_thresh)
In order to obtain the spur-reduction benefits of shuffling at large signal levels while
retaining the low noise of not shuffling when the signal is small, the AD6676 supports
dynamic shuffle control via the Shuffle Threshold attribute.
Shuffling is disabled if the raw ADC output is below the specified threshold for ~5000 clock cycles.
A threshold of zero implies that shuffling is always enabled.
The supported range is from 0..8
This specifies any shell prompt running on the target
root@analog:/sys/bus/iio/devices/iio:device1# cat in_voltage_shuffler_thresh_available 0 1 2 3 4 5 6 7 8 root@analog:/sys/bus/iio/devices/iio:device1# cat in_voltage_shuffler_thresh 5 root@analog:/sys/bus/iio/devices/iio:device1# echo 4 > in_voltage_shuffler_thresh root@analog:/sys/bus/iio/devices/iio:device1# cat in_voltage_shuffler_thresh 4
Test Modes (in_voltage_test_mode)
Interface test modes supported by the AD6676.
This specifies any shell prompt running on the target
root@analog:/sys/bus/iio/devices/iio:device1# cat in_voltage_test_mode_available off checkerboard one_zero_toggle pn23 pn9 rep_user_pat sing_user_pat ramp mod_rpat jspat jtspat root@analog:/sys/bus/iio/devices/iio:device1# echo ramp > in_voltage_test_mode root@analog:/sys/bus/iio/devices/iio:device1# cat in_voltage_test_mode ramp
JESD Interface Testing
More Information
- IIO mailing list: linux [dash] iio [at] vger [dot] kernel [dot] org
resources/tools-software/linux-drivers/iio-adc/ad6676.1455221273.txt.gz · Last modified: 11 Feb 2016 21:07 by Lars-Peter Clausen