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Evaluation Kit for the CMX998

EV9980


Features:

  • Allows Full Evaluation of the CMX998 IC
  • Operational Frequency Range: 100MHz to 1GHz
  • Complete Demonstration of CFBL Functionality
  • Access to RF, Control and Baseband Signals
  • Support and Interfacing for Customer PAs
  • Differential or Single-ended I and Q Inputs
  • 360 Loop Phase Shift Control
  • Can utilise PE0003 EvKit interface to work with a PC or can be used with custom interface equipment

Applications:

  • For the Evaluation, Demonstration and Design-In of the CMX998

Supply Requirement:

  • 7.2V (typ) power supply
  • 1.2V and 3.6V for on-board RF PA

The EV9980 EvKit allows rapid and full evaluation of the CMX998 Cartesian Feedback Transmitter IC.

In the form of a populated PCB, this flexible platform enables users, using a control interface, to configure and evaluate the CMX998 to various applications and frequency bands.

Access is provided to all CMX998 RF, baseband and control signals by either connector or test points. Test access points are available to accept common test equipments such as RF and baseband signal generators and spectrum analysers.

All signal paths are matched by suitable components and the EvKit provides a power amplifier (PA) device at 450MHz which can be modified to provide operation at 800MHz. The EvKit can also be configured for an external PA. The overall operating evaluation frequency range of the EvKit is for RF frequencies between 100MHz and 1GHz.

The EV9980 can be configured to work with the CMX981 Digital Radio Baseband processor IC, standard test equipment or with a custom baseband system.

No software is required for use of the EvKit; the on-board CMX998 is controlled via its C-BUS serial interface and control system. This can be controlled by a PE0003 interface card (available separately) or, alternatively, a custom C-BUS interface and control system can be used.


PCB Image

EV9980 EvKit: For the Evaluation, Demonstration and Design-In of the CMX998 IC

Design Support Information

 

EV9980 FAQ
 

Q. When using the CMX998 Cartesian loop IC with its evaluation kit (EV9980) I have seen degradation in carrier leakage when I enable the RF detector after the DC calibration phase.
What can I do to ensure a stable carrier leakage when I enable the RF detector?

A. In some configurations of the EV9980 the DC offset adjustment appears degraded when DCMEAS is set to "0" to "1".
That is to say when the RF detector output is connected to the DCMEAS pin following a DC calibration procedure. The cause of this is internal offsets that result in a small, (nominally 5mV), shift in VREF and BVREF when the change is made.
The effect is shown in Table 1 (below):



DC On RF Det. DCMEAS Carrier leakage with DC offset adjusted on
RV1/RV2 with Fixed bias offset
(Note 1)
Carrier leakage with DC offset adjusted on
RV1/RV2 with BVREF used for bias offset
(Note 2)
1 0 0 -33dBm (-63dBc) -26dBm (-56dBc)
1 1 0 -33dBm (-63dBc) -27dBm (-57dBc)
0 1 0 -24dBm (-54dBc) -27dBm (-57dBc)
0 1 1 -4dBm (-34dBc) -22dBm (-52dBc)
1 1 1 -4dBm (-34dBc) -22dBm (-53dBc)
0 0 1 -23dBm (-53dBc) -28dBm (-58dBc)

Table 1 - Carrier leakage achieved with for various conditions of DCMEAS and associated control signals, PA enabled (+30dBm mean power with modulation), 450MHz, Divide by 2 LO.

The transmitter is configured for +30dBm mean output power, TETRA pi/4-DQPSK or two-tone modulation, so a carrier null of 33dBm is -63dBc, where 'c' is based on the mean signal power.
When DCMEAS = '1' and the RF detector is enabled a degradation in carrier offset is observed with a previously adjusted carrier-null. This effect can be avoided by using BVREF to bias the input signal rather than using a resistor network tied to 3.3V.

With PCB555D in 'Mod State' 3 or 5 the BVREF signal is already used to bias the input signal in single ended mode. This means a common shift is applied to DC offset correction signal and modulator reference. The results from this improved configuration are also shown in Table 1 and although a small degradation is still observed the carrier leakage is still -52dBc, which is considered more than adequate for most applications.

Figure 1 and Table 2 show what modifications are required to be made to EV9980 Evaluation Kits which are not Mod State 3 or 5 and so which have not already been modified to allow VBREF biasing of the input signal. Both Single Ended and Differential modes are shown.

981


Figure 1 - Signal Input Layout

Connection Q I Replacement Value
(Ohms)
EV9810 to EV9980 R5 R57 5k1
Single-ended Connection R7 R53 Not Fitted
BVREF Biased R9 R51 Not Fitted
R13 R45 5k1
R14 R44 Not Fitted
R97 R100 10k1
EV9810 to EV9980 R5 R57 47k
Differential Connection R7 R53 Not Fitted
BVREF Biased R9 R51 100k
R13 R45 47k
R14 R44 100k
R97 R100 Not Fitted

Table 2 - Modified Component Values.

Figure 1 and Table 2 show what modifications are required to unmodified EV9980 Evaluation Kits (e.g., Mod State 4) to allow VBREF biasing of the input signal.
Both Single Ended and Differential modes are shown.


Q. Are there any particular aspects of power-up or down sequence of the EV9980 that I should be aware of?

A. There is nothing specific to be aware of when powering the EV9980 up for the first time, however it is very important to ensure that a 50ohm load is attached to J9 before enabling the power amplifier.
The PA device is not protected and enabling this device without the load may irreparably dame the device.

There is a preferred method of powering down the EV9980 to also avoid damage to the power amplifier (PA).
This is because, if the PA is powered down before the CMX998, the PA can be overdriven to the point of failure. The output power will decrease once the PA is powered down, and this results in a lower signal level fed back into the CMX998.

The error amplifier input signal levels will diverge, so the error signal to the up converter will increase, and the signal level to the PA input will also increase.
This process will continue as the PA output ramps down, with the up converter output and PA input signal level continuously increasing.
This can over-drive the PA which may over-current and fail.

The recommended way to avoid this is to power-down the CMX998 down-converter before powering down the PA.
Within the EV9980 GUI software, clearing the "Feedback Path En." box ("CMX998 Regs ($01-$06)" tab) and clicking on "Write Gen Ctl Reg" will powerdown the CMX998 down-converter.


Signal Levels
Q. I am just starting to investigate the CMX998 and am using an EV9980 Evaluation Kit. Do you have any recommended signal-levels that will allow me to see the CMX998 at its best?

A. The Cartesian Feedback Loop IC, CMX998 does indeed have an optimal operating range.
The hyperlinked illustration (EV9980 Levels) shows what signal levels we recommend and where measurements may be taken when using the EV9980. It is always recommended that you refer to the current EV9980 User Manual and the CMX998 Datasheet regarding use and set-ups.

 
 
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