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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Included are forward and feedback paths; local oscillator circuitry including loop phase control; an instability detector and uncommitted op-amps for input signal conditioning. Note that a different loop-filter might be required for the kHz and kHz channels. 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 measurements include the effects of the non-ideal PA that is corrected by the Cartesian loop.
There is a preferred method of powering down the EV to also avoid damage to the power amplifier PA. This effect can be avoided by using BVREF to bias the input signal rather than using a resistor network tied to 3. This means a common shift is applied to DC offset correction signal and modulator reference. A simple guide to help users get started evaluating the EV The PA device is not protected and enabling this device without the load may irreparably dame the device.
EV high resolution schematics and component overlay. We use cookies to ensure that we give you the best experience on our website.
CMX998 – Cartesian Feedback Loop Transmitter
This App Note discusses these issues using the DE in a worked example. The data will appear in the grayed-out data box. These scripts require the following evaluation boards: The wideband noise of the CMX alone at 5MHz offset is typically somewhat better than shown in this plot.
The effect is shown in Table 1 below: What can I do to ensure a stable carrier leakage when I enable the RF detector? The effect is shown in Table 1 below:. Using a Cartesian transmitter in TDMA systems can be challenging when supporting multiple modulation formats.
The modulation accuracy of a CMX transmit is determined by the down-converter feedback path. This can over-drive the PA which may over-current and fail.
CMX – Cartesian Feedback Loop Transmitter – CML Microcircuits
The CMX instability detector cannot detect lead or lag error as it works on a simple baseband signal. Can you help explain how the instability datzsheet on the CMX operates and how it can be used? For clarification, the relevant change is: If the loop is set up degrees out of phase the loop will oscillate and will generally produce a maximum level carrier. Three scripts for evaluating performance of a multi-mode modem using the DE 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.
This issue can be greatly reduced if the alternative configuration for applying a bias voltage to the input signal is used, dayasheet documented in EV Datasheet version 5 and above. The CMX includes gain adjustment to make threshold setting easier.
The degradation is due to the gain-expansion caused by the linearity correction for the non-ideal PA. The recommended way to avoid this is to power-down the CMX down-converter before powering down the PA. 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. Datasheets CMX Datasheet rev Do you have any recommended signal-levels that will allow me to see the CMX at its best?
The instability detector comprises a high-pass filter followed cmx9998 a peak-detector circuit and this combination indicates the presence of this high frequency energy. The error signal produced by the instability detector should be accessed for a particular design and an appropriate threshold set. The instability detector is designed to detect minor phase variations and resultant instability following initial phase correction. There are three CMX internal registers that are key for this discussion: A simple guide to help datashheet get started evaluating the DE Such effects are unlikely to cause a phase shift as large as degrees.
These scripts can be easily modified to support other Block Types. I am looking to develop a high quality non-constant envelope transmitter and am looking to improve the linearity of my current design. If you continue to use this site we will assume that you are happy with it. This process will continue as the PA output ramps down, with the up converter output and PA input signal level continuously increasing. As phase error increases, the instability detector will show a worsening level of out-band energy.
Technical Portal No additional information available. Are there any particular aspects of power-up or down sequence of the EV that I should be aware of? If instability is detected then normal procedure is to power down the transmitter. It is important to read the included readme. 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.
There is nothing specific to be aware of when powering the EV 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. As this is effectively a stable oscillating condition the instability detector will not detect this operating state. 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.
If the loop becomes unstable due to phase inaccuracies the feedback loop will tend to spill energy out-of band.
Typical changes are variations in antenna VSWR and thermal effects. Both Single Ended and Differential modes are shown.
