Download Input structure of AS3990

Input structure of AS3990 ...........................................................................................................4
What is worst case sensitivity and Sensitivity Measurement .................................................4
What are the assumptions in the sensitivity testing? ..............................................................4
What is the 1dB compression point ........................................................................................4
What input linearity specification do you have?.....................................................................5
What Filter settings can you alter?..........................................................................................5
Maximum input level at AS3990 ............................................................................................5
Is Vcc really 5.3V typical and not 5.0V typical ......................................................................5
Do I always need a circulator? ................................................................................................5
What is the effect of the Automatic gain control (AGC) ........................................................5
What is the difference between AGC and AGL .....................................................................6
What is the procedure for improving Tag reception? .............................................................6
What are the Limitations on tag reception? ............................................................................6
What is the calculation for the measurement of the reflected power ...................................6
How to check the sensitivity level? ........................................................................................6
Can I use RSSI ........................................................................................................................6
Can I get an idea of the reflected power out of the chip? .......................................................7
Does AGC automatically switch on the internal attenuator? ..................................................7
How is internal attenuator controlled in the AS3990 Eval. KIT? ...........................................7
Frequency generation block ........................................................................................................7
How to connect the external 20MHz clock source? ...............................................................7
How to design a loop Filter? ...................................................................................................8
What is PLL lock time? ..........................................................................................................8
What is the needed loop bandwidth for the system?...............................................................8
What is the recommendation regarding the load capacitors of the Crystal load? ...................8
What is usable output voltage range of charge pump? ...........................................................8
What is VCO phase noise level for internal AS3991 VCO? ..................................................8
How to observe a locked PLL? ...............................................................................................8
Did the AS3990 support the new Chinese frequencies ...........................................................8
Output amplifier and structure ....................................................................................................9
Which linearity is given provided at internal Power amplifier ...............................................9
What kinds of Filters are being used on the Transmit side? ...................................................9
What is the matching impedance of the PA - outputs? ...........................................................9
What are the details of the current consumption in case a external PA of 23 dBm is being used
.................................................................................................................................................9
What is the additional current consumption using the internal PA? .....................................10
Can internal 20dBm PA be programmed/changed by any means? .......................................10
Regarding antenna design, is it possible to change status of Tx and Rx by digital switch ? 10
They will need Antenna design guide, can you provide it? ..................................................10
Is the 20 dB output power the linear point or max emitted power, give graph of the PA output 10
Is it possible to control OBW value? If possible, how is the value? ....................................10
How to use the low power output (0dBm) ............................................................................11
Is it possible to adjust the RF output power? ........................................................................11
Is it possible to monitor the RF output power? .....................................................................11
Can AS3992 meet the DRM mask? ......................................................................................11
Which modulation mode should be used in AS399x to meet the ETSI TX spectrum mask?11
Which modulation mode should be used in AS399x to meet the DRM TX spectrum mask?11
ETSI demands very low spurious emission in terrestrial TV and radio bands. Does AS399x fulfil
this requirement? ...................................................................................................................12
Do we need external filter on the TX output to filter the harmonics? ..................................12
What OBW the AS3990/901G achieves? .............................................................................12
Does the modulation stage use IQ up-conversion or direct conversion? ..............................12
What is appropriate load for the RF outputs? .......................................................................12
How to use low power output in single ended configuration?..............................................12
Can we supply the RFOPX and RFONX from 5V supply?..................................................13
Software related questions ........................................................................................................13
Can I use maximum gain setting to increase Tag reception .................................................13
What are the standard settings for Software .........................................................................13
Does the AS3990 support frequency hopping (a requirement in the US) ............................13
Can you supply some instruction in source code to support the IC functions to Tag? .........14
How is the chip dealing with anti-collision?.........................................................................14
How can long data’s been sent? ............................................................................................14
How fast can the SPI being clocked? ....................................................................................14
What is the 15th Byte I read after the EPC? .........................................................................14
Commercial and project related costsQuote for Eval board .................................................14
Quote for Eval board .............................................................................................................15
What is the pricing for the reader chip? ................................................................................15
Availability of Eva-Board .....................................................................................................15
Reference design of AS3990 demo board, can you provide it? ............................................15
Availability of samples- mass production.............................................................................15
General questions ......................................................................................................................15
How is the chip communication with the controller? ...........................................................15
What are the noise sensitive pins in the system in which customer must take precautions in the
layout? ...................................................................................................................................16
How can the sensitivity be increased? ..................................................................................16
What is the contribution of Jamm signal ?............................................................................16
How the VCO phase noise affects the RFID system operation? ..........................................17
When will AMS have EPC standard test data from external, qualified lab ..........................17
What are steps to make my board working ...........................................................................17
What is the needed time to power up the whole system? .....................................................17
Do we have the numbers available how long it takes to get from power down mode to TX mode
(until the PA is settled so that a communication with a TAG can be started) and vice versa and
from standby mode to transmit mode and vice versa ...........................................................18
What are the possibilities of the clock sources of the chip? .................................................18
How to deal with issues of current chip and plans are for next release of the chip? ............18
Do you have recommendations of designing a board? .........................................................19
Can the chip operate in a Dense Reader Mask environment ? .............................................19
Blocker and co-channel performance?..................................................................................19
How will the device perform against the EPC requirements? ..............................................19
What is the best RFID frequency? ........................................................................................19
What is Near-Field UHF? .....................................................................................................19
Do you have test results with ambient noise such as florescent light? .................................20
What runs from what supply and how much? ......................................................................20
DAC and ADC-Description ..................................................................................................20
DAC Resolution of the integrated ADC/DAC......................................................................20
If reading the Tag at EPC class-1, Gen-2 Tag, what’s the maximum speed using AS3990 EV KIT?
...............................................................................................................................................20
What kind of Tag’s and silicon have you already tested? ....................................................20
How can I debug the chip?....................................................................................................20
If the Header bit in the IRQ status is high, where is the error code from the tag stored? .....21
How to achieve good Rx to Tx isolation ? ............................................................................21
Which configurations using AS3990/AS3991 are proposed regarding external components.22
Why the AS3990 is proposed to be used with external VCO? .............................................22
Can we use directional coupler instead of circulator? ..........................................................22
Can we put antenna on the same PCB as AS3990/AS3991? ................................................22
What is the benefit of the mono-static operation compared to the bi-static?........................23
What determines the range of the RFID system? .................................................................23
How can we increase the operating range of the RFID system? ..........................................23
We have difficulties to buy a good antenna. .........................................................................23
We are using OAD,OAD2 outputs to observe BB analogue signals. We see unwanted signals in
the filter pass band. Can this be a reason for bad reception? ................................................24
We are designing RFID system. How we can check which parameter is limiting the operating
range? ....................................................................................................................................24
Is it possible to use external LNA? .......................................................................................24
Does AS3990/AS3991 support LBT? ...................................................................................24
Can customer add external receiver chip to implement LBT functionality? ........................24
Protocoll stack ...........................................................................................................................25
Can I receive commands with and without header Bits? ......................................................25
Which EPC Gen2 setting should be used for best performance? .........................................25
Can I use special commands for NXP Tag's .........................................................................25
As to Anti-Collision mechanism, how many tags can be detected per second by AS3990? How
this mechanism works? .........................................................................................................25
How did the anti-collision work? ..........................................................................................26
Can AS3990 support ISO 18000 6b......................................................................................26
Can I use other protocols than EPC c1g2?............................................................................26
Can AS3990/AS3991 access the EM UHF tag’s? ................................................................26
How to send EPC Gen2 Select command? ...........................................................................26
How to send EPC Gen2 Query command? ...........................................................................27
How to send EPC Gen2 Ack command? ..............................................................................27
How to use Query and Ack? .................................................................................................27
Is 24 byte FIFO deep enough to transfer data needed in EPC Gen2?...................................28
While processing some data with an interrupt method, Could you process anti-Collision? 28
How to deal with interference tones in multi-reader environments cochannel (two readers on same
channel) performance............................................................................................................28
What are the margins in the mask compliance?....................................................................28
Do you fulfil the ETSI mask with AS3990 ...........................................................................29
Do you have the conformance performance over whole band. ............................................31
Does AS3990 separate in a transmit FIFO and receive FIFO? .............................................31
Does a direct command RESET FIFO(0x8F) clear both the transmit and receive FIFO? ...31
How much of power from the Tag the chip can acccept ?....................................................32
How can the output spectrum being optimized ? ..................................................................32
Controller related questions ......................................................................................................32
What MCU properties are needed to control the AS3990? ..................................................32
What needs to be done to port the code from the MSP to another MCU? ...........................33
Are there software updates available for the GUI and for the MCU board? ........................33
Is it allowed to supply MCU from one of the on-board regulators? .....................................33
POWER SUPPLY .....................................................................................................................33
Why 5.3V is proposed typical VEXT supply voltage? .........................................................33
Is it possible to operate at lower supply voltage? .................................................................33
What is power consumption of the AS3990/AS3991 in power down mode and in operation? 34
PCB LAYOUT, DEBUG ..........................................................................................................34
How to copy the AS3990 Eval. KIT RF board? ...................................................................34
How many layer PCB in needed for the AS3990/AS3991 RF board? .................................34
What are the sensitive pins in the system in which customer must take precautions in the layout?
...............................................................................................................................................34
Is two layer PCB sufficient for the AS3990/AS3991? .........................................................35
Which are VCO and PLL sensitive pins we need to take care when designing our PCB? ..35
Which rules should be followed when designing a PCB regarding pin-to-pin cross-talks? .35
On my PCB the IO lines to the MCU lies below the loop filter. It this allowed? ................35
When designing a PCB, which pins should be accessible for measurement and debug? .....35
We would like to prepare on board antenna and SMA connector on the same PCB. What you
suggest? .................................................................................................................................35
How to start debug our own PCB? .......................................................................................36
Input structure of AS3990
What is worst case sensitivity and Sensitivity Measurement
Measurement gave -66 dBm., but sensitivity is limited by TX noise which is output power
dependent.
RX sensitivity is -66dBm on the differential mixer input and -73dBm on a single ended input mixer.
Since the transponder's responses are typically higher than this levels, we normally use internal (in
chip) attenuator switched on and sensitivity of -58dBm on the Eval. kit. In case the reflected power is
low (we can internally measure the level of reflected power) we change the sensitivity to -66dBm
during inventory round to get some more distant tags.
The mixer inputs are optimized to relatively high input level (1dBcp at 13dBm), since usually the
main problem at mixer input is reflected carrier power caused by un-perfect antenna match and
circulator leakage. The reflected carrier power increases the received noise floor, or in worst case
overloads the mixer. Typically the sensitivity is not the main limiting factor for the system
performance.
What are the assumptions in the sensitivity testing?
Since the performance of a RFID system must always be seen with the self jamming part, we have to
find a way to separate the receiving chain to the transmitting self jamming part. This can be done
provide two possibilities: A simulation and a testing setup with a PLL tuned to a frequency a
frequency generator tuned to a frequency of PLL plus an offset of link frequency. The received I and
Q signals were observed in terms of signal quality. The level of frequency generator is reduced to a
level in which the baseband signal will be corrupted. This measured value will be valid up to a few
dBm of self jam power (probably ~5-7 dB). Then the noise of the transmitted signal will becomes
majority of sensitivity jeopardizing.
What is the 1dB compression point
The 1 dB compression point is a linearity figure of the input mixer and specifies generally the
maximum input power on which a device will be operable. The mixer 1dB c.p. without attenuator is
high, above 10dBm (typically 13dBm), with on-chip input attenuator even higher.
1dBCp for current mixer (v2, and v3 at 4.8V supply) is 13dBm without internal attenuator, with
attenuator mixer can be used to up to 17dBm.
What input linearity specification do you have?
We have two input configuration's which are single and differential ended:
For differential mixer we measured IP2=+32dBm, IP3=+20..22dBm depending on input conditions.
For single ended mixer we measured IP2=+24dBm, IP3=+19..21dBm.
Those samples had the 1dBcp at +10- +11dBm. With the improvements on the chip the 1dBcp was
moved to ~13dBm. Our 1dB compression pint is 17 dBm. With an additional attenuator we can
handle self jammer up to + 17 dBm.
What Filter settings can you alter?
fl<2:1> setting=00, 3dB bandwidth: 6...160kHz fl<2:1> setting=01, 3dB bandwidth: 15...270kHz
fl<2:1> setting=10, 3dB bandwidth: 40...580kHz fl<2:1> setting=11, 3dB bandwidth: 100...900kHz
RTcal has 4 settings in reg02 for each Tari (together 12 combinations).
TRcal has range 17us...409us, step 0.1us in reg04 and 05.
ASK and PRASK (Tari=25us) spectrum shapes acquired on one AMS board are attached.
Maximum input level at AS3990
The input mixers are supplied with 5 Volt which enables the opportunity to handle also high
dynamic range on its input. Currently the Device can handle a maximum input level at +10 dBm at
50 Ohm, which is respective a voltage of approximately 2 Vss.
Is Vcc really 5.3V typical and not 5.0V typical
Although the device will work at even 4.5 Volt and below the best performance in terms of RX input
stage supply rejection will be achieved when the internal regulator that feeds the input RX mixer
stage has enough headroom. This internal regulator requires the highest voltage regulator on chip
and is only used on the input stage. All other internal blocks which requires >95% of the total current
consumption of device will be supplied by other lower voltage regulators (3.3V and 2.5V).
Do I always need a circulator?
No, because an isolation is needed to increase the performance of the system. As the noise of the
transmit stage jeopardize the tag signal to noise ratio on the receiver, we need an isolation for a high
performance. In this respect we recommend using always a directional unit which can be a circulator
or a directional coupler. The Device can handle common mode levels of up to 10Bm. Using the
internal attenuation the received signal can be even up to +20dBm. However, special care needs to
be taken on the amplitude noise which is generated on the sending stage. This noise needs to be less
than the signal from the Tag.
At input level 0dBm (reflected power) you do not need an internal attenuator.
What is the effect of the Automatic gain control (AGC)
AGC affects gain and digitizing hysteresis only, using the AGC is dependant on received signal.
The attenuator can not be switched on automatically. You can decide to use it if you expect high
reflected power (design, environment) or by measuring mixer DC level by internal ADC.
What is the difference between AGC and AGL
What is the procedure for improving Tag reception?
Tags can be far away or close to the Antenna. Depending on the range, the signal strength will be
different. It can also be that the Tag closer to the Antenna will override the Tag far away. Therefore
we used in our demo boards initially the internal attenuator with slightly increased hysteresis on
which suppresses weak Tag signals. We start the standard anti-collision procedure using “select”,
“query”- commands thus pick the transponders in the range. After this we decrease hysteres to
minimum, and in case the two mixer DC levels that shows reflected energy replies a lower value
than 20...25 we also remove the attenuator and transmit another query (without select) and some
query_reps to get tags that are more far away, but still in range of reception.
What are the Limitations on tag reception?
The main restriction in range is the power that is needed on the Tag. Even with improved tag design,
we can calculate a required sensitivity of – 60 dBm on the reader side which will be easily achieved
from AS3990. The main problem on reader side will be the noise generated by the transmitter. As the
transmitted power will be at -30 dBm and the backscattered signal will be in the range of -40 dBm
and a signal to noise ratio of at least 20 dBm is needed, we will need a signal to noise ratio on the
transmitter side of over 90 dBm. This value can be reduced with the isolation factor of the circulator.
This makes also clear, that special care must be taken in the sending stage of the Transmitter.
Typically the RFID problem is not that the mixer will be overloaded. The problem is moreover noise
of the transmitted-reflected carrier which is demodulated in a receiver. External PA is usually the
main source of noise and in case the reflected power is more than ~10dBm this demodulated noise
becomes too high and internal attenuator needs to reduce it.
What is the calculation for the measurement of the reflected power
Approximate formula for received reflected power is Pin (dBm)=20*log(ADC-value/G), where
ADC-value is absolute value of the two mixer DC level numbers from ADC and G is constant
depending on ir<1:0> bits in reg. 0A (G=19.6 for ir=00, G=20.8 for ir=10, G=8.2 for ir=01 and 11).
The bit ir<1> will not be supported in the final chip since it does not help much in application.
How to check the sensitivity level?
The sensitivity can be measured by connecting CW RF signal generator to the antenna input. RF
source frequency should be set to a local oscillator frequency increased for the targeted link
frequency. The integrity of the down converted and digitized signal (OAD, OAD2) is observed. The
sensitivity level is the lowest input signal level at which all transitions on the OAD and OAD2 are
still present. In case the reflected TX signal is present up to 5dBm at the receiver’s input, the
sensitivity is negligibly corrupted. Further on, up to 10dBm reflected carrier level, the receiver can
operate, but the noise demodulated from the reflected carrier becomes more and more important. At
reflected power level 10dBm and above, the noise demodulated from the reflected carrier becomes
the dominant noise source corrupting the sensitivity.
Can I use RSSI
The RSSI information of previous reception stays stored in RSSI register until the next reception –
Can I get an idea of the reflected power out of the chip?
-Yes, analogue signals are available on OAD/OAD2 in case you set e_anasubc bit in reg14. There
you can observe signals, noise, AGC action... Note that first 3 steps in AGC are not seen on signal
since these steps are done on digitizer. In case you set subc_out bit in reg11 on OAD/OAD2 the
digitized sub carrier is seen, note that these are 5V outputs or open drain NMOS outputs. In case you
set e_anamix on the OADs the mixer DC levels are available - the same ones that are used for ADC
conversion.
Does AGC automatically switch on the internal attenuator?
No. AGC reacts on level of received signal and affects base band gain and digitizing hysteresis. The
attenuator can be switched on by the MCU. It can decide to use attenuator in case high reflected
power is expected (design, environment) or, better, by measuring the down converted reflected
power as mixer DC level. The onboard ADC is used to acquire the reflected power level in both
channels.
How is internal attenuator controlled in the AS3990 Eval. KIT?
In an the Eval Kit we start inventory round with sensitivity of -59dBm and collect most of the tags.
In case the reflected power is relative low (<5dBm, at this RF level the noise contribution from the
carrier demodulation is not the dominant noise source), we switch off the internal input attenuator
and continue inventory round with sensitivity of -66dBm, and maybe find something else. Reflected
power and signal strength can both be measured with our chip, so MCU can decide how to control
the receiver parameters dynamically. There are also possibilities of manual gain adjustment, AGC
(auto gain adjustment to optimum signal level at the receiver output, updated for each packet), or
AGL (auto gain adjustment to a level at which the received noise and interference level is just below
the digitizer threshold, updated on request). In different cases different possibilities can perform
best.
Frequency generation block
How to connect the external 20MHz clock source?
External 20MHz clock source (like TCXO) is required to achieve good frequency accuracy. It
should be connected to OSCO pin. DC level should be approximately 1.7V (half of the VDD_D
supply voltage, in case the external signal is AC coupled the DC level is correctly set by internal
circuitry). Amplitude should be 1Vpp or higher. Shape should be approximately sinusoidal. OSCI
pin should be open.
There are a few possibilities how to connect TCXO output to the OSCO pin:
• Optimum solution is to connect sinus shaped TCXO signal to the OSCO pin via AC coupling
capacitor.
• Connect square shaped TCXO signal via AC coupling capacitor and low pass filter. Typically
second (or higher) order is needed. PCB layout is critical for good suppression of higher harmonics.
In case the harmonics are not filtered out they can appear in the output spectrum.
• Connect square shaped TCXO signal with low level 0V and high level 3.3V directly to the
OSCO pin. Issues are expected since content of higher harmonics of any square signal that is
connected to IC pins or in proximity of the IC couples to the output signal. From operation point of
view the TCXO-OSCO direct connection is possible but output spectrum might be corrupted. Such
application is possible for less demanding applications only.
How to design a loop Filter?
Current Kvco is 200MHz/V for the AS3990 and 20 MHz/Volt for the AS3991, input capacitance on
Pin VCO is 50pF. We propose to use third order loop filter. The filter values for internal VCO will be
given in the demo board schematic and application example as well as in the app note of
VCO-usage.
What is PLL lock time?
PLL lock time is 300µs. Automatic VCO range select procedure in AS3991 can take up to 6 ms.
In time critical applications it is possible to measure the actual VCO voltage and previously selected
VCO range and predict and manually prepare correct VCO adjustment for next frequency step. In
such case frequency hop time remains at 300µs
What is the needed loop bandwidth for the system?
We use 1/10 of the reference frequency for the loop BW. Using 100 kHz we propose to use 10 kHz
Loop Bandwidth.
What is the recommendation regarding the load capacitors of the
Crystal
Can I use RSSI
The RSSI information of previous reception stays stored in RSSI register until the next reception
–
Can I get an idea of the reflected power out of the chip?
-Yes, analogue signals are available on OAD/OAD2 in case you set e_anasubc bit in reg14. There
you can observe signals, noise, AGC action... Note that first 3 steps in AGC are not seen on signal
since these steps are done on digitizer. In case you set subc_out bit in reg11 on OAD/OAD2 the
digitized sub carrier is seen, note that these are 5V outputs or open drain NMOS outputs. In case
you set e_anamix on the OADs the mixer DC levels are available - the same ones that are used for
ADC conversion.
Does AGC automatically switch on the internal attenuator?
No. AGC reacts on level of received signal and affects base band gain and digitizing hysteresis.
The attenuator can be switched on by the MCU. It can decide to use attenuator in case high
reflected power is expected (design, environment) or, better, by measuring the down converted
reflected power as mixer DC level. The onboard ADC is used to acquire the reflected power level
in both channels.
How is internal attenuator controlled in the AS3990 Eval. KIT?
In an the Eval Kit we start inventory round with sensitivity of -59dBm and collect most of the tags.
In case the reflected power is relative low (<5dBm, at this RF level the noise contribution from the
carrier demodulation is not the dominant noise source), we switch off the internal input
attenuator and continue inventory round with sensitivity of -66dBm, and maybe find something
else. Reflected power and signal strength can both be measured with our chip, so MCU can decide
how to control the receiver parameters dynamically. There are also possibilities of manual gain
adjustment, AGC (auto gain adjustment to optimum signal level at the receiver output, updated
for each packet), or AGL (auto gain adjustment to a level at which the received noise and
interference level is just below the digitizer threshold, updated on request). In different cases
different possibilities can perform best.
Frequency generation block
How to connect the external 20MHz clock source?
External 20MHz clock source (like TCXO) is required to achieve good frequency accuracy. It
should be connected to OSCO pin. DC level should be approximately 1.7V (half of the VDD_D
supply voltage, in case the external signal is AC coupled the DC level is correctly set by internal
circuitry). Amplitude should be 1Vpp or higher. Shape should be approximately sinusoidal. OSCI
pin should be open.
There are a few possibilities how to connect TCXO output to the OSCO pin:
• Optimum solution is to connect sinus shaped TCXO signal to the OSCO pin via AC
coupling capacitor.
• Connect square shaped TCXO signal via AC coupling capacitor and low pass filter. Typically
second (or higher) order is needed. PCB layout is critical for good suppression of higher
harmonics. In case the harmonics are not filtered out they can appear in the output spectrum.
• Connect square shaped TCXO signal with low level 0V and high level 3.3V directly to the
OSCO pin. Issues are expected since content of higher harmonics of any square signal that is
connected to IC pins or in proximity of the IC couples to the output signal. From operation point
of view the TCXO-OSCO direct connection is possible but output spectrum might be corrupted.
Such application is possible for less demanding applications only.
How to design a loop Filter?
Current Kvco is 200MHz/V for the AS3990 and 20 MHz/Volt for the AS3991, input capacitance
on Pin VCO is 50pF. We propose to use third order loop filter. The filter values for internal VCO
will be given in the demo board schematic and application example as well as in the app note of
VCO-usage.
What is PLL lock time?
PLL lock time is 300µs. Automatic VCO range select procedure in AS3991 can take up to 6 ms.
In time critical applications it is possible to measure the actual VCO voltage and previously
selected VCO range and predict and manually prepare correct VCO adjustment for next
frequency step. In such case frequency hop time remains at 300µs
What is the needed loop bandwidth for the system?
We use 1/10 of the reference frequency for the loop BW. Using 100 kHz we propose to use 10 kHz
Loop Bandwidth.
What is the recommendation regarding the load capacitors of the
Crystal load?
Load capacitors are related to crystal more than to the chip. We propose to use crystals that
require load capacitance less than 20pF and have a serial resistance less than 30ohm. Note that
the chip already provides a load capacitance with ~5pF on each side. You have to take it account
by calculating the required load capacitance.
What is usable output voltage range of charge pump?
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