As a state-of-the-art design for an integrated CFBL, the CMX improves the . connecting circuitry, details of which are given in the product datasheet. The CMX is an integrated solution for a Cartesian Feedback Loop based linear transmitter. Acting as a direct conversion quadrature mixer from I and Q to RF. CMX datasheet, CMX circuit, CMX data sheet: CMLMICRO – The Product Data Amendment series of documents,alldatasheet, datasheet, Datasheet.
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The instability detector c,x998 a high-pass filter followed by a peak-detector circuit and this combination indicates the presence of this high frequency energy. This App Note discusses these issues using the DE in a worked example.
The effect is shown in Table 1 below:. Typical changes are variations in antenna VSWR and thermal effects. If the loop becomes unstable due to phase inaccuracies the feedback loop will tend to spill energy out-of band.
The PA device is not protected and enabling this device without the load may irreparably dame the device. Using a Cartesian transmitter in TDMA systems can be challenging when supporting multiple modulation formats. This can over-drive the PA which may over-current and fail. Both Single Ended and Differential modes are shown.
The error signal produced by the instability detector should be accessed for a particular design and an appropriate threshold set. If the loop is set up degrees out of phase the loop will oscillate and will generally produce a maximum level carrier.
These scripts require the following evaluation boards: Note that a different loop-filter might be required for the kHz and kHz channels. The modulation accuracy of a CMX transmit is determined by the down-converter feedback path. This process will continue as the PA output mcx998 down, with the up converter output and PA input signal level continuously increasing.
The measurements include the effects of the non-ideal PA that is corrected by the Cartesian loop.
CMX – Cartesian Feedback Loop Transmitter – CML Microcircuits
There are three CMX internal registers that are key for this discussion: Included are forward and feedback paths; local oscillator circuitry including loop phase control; an instability detector and uncommitted op-amps for input signal conditioning.
Are there any particular aspects of power-up or down sequence of the EV that I should be aware of? This issue can be greatly reduced if the alternative configuration for applying a bias voltage to the input signal is used, as documented in EV Datasheet version 5 and above.
This means a common shift is applied to DC offset correction signal and modulator reference. If instability is detected then normal procedure is to power down the transmitter.
The output power will decrease once the PA is powered down, and this results in a lower signal level fed back into the CMX 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 dBc, which is considered more than adequate for most applications.
The data will appear in the grayed-out data box. Can you help explain how the instability detector on the CMX operates and how it can be used? It is important datawheet read the included readme. The recommended way to avoid this is to power-down the CMX down-converter before powering down the PA.
For clarification, the relevant change is: If you continue to use this site we will assume that you are happy with it. The effect is shown in Table 1 below: The instability detector is designed to detect minor phase variations and resultant instability following initial phase correction.
CMX998 – Cartesian Feedback Loop Transmitter
A simple guide to help users get started evaluating the DE If a design supports dynamic loop phase calibration then an instability detector event normally triggers loop re-calibration. I am looking to develop a high quality non-constant envelope transmitter and am looking to improve the linearity of my current design. Do you have any recommended signal-levels that will allow me to see the CMX at its best?
In the form of a populated PCB, this flexible platform enables users, using a control interface, to configure and evaluate the CMX to various applications and frequency bands. What can I do to ensure a stable carrier leakage when I enable the RF detector? The instability detector found on the CMX is a relatively simple mechanism that measures the level of out-of band energy of the feedback loop.
EV high resolution schematics and component overlay. Such effects are unlikely to cause a phase shift as large as degrees. As this is effectively a stable oscillating condition the instability detector will not detect this operating state. There is a preferred method of powering down the EV to also avoid damage to the power amplifier PA.