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. The modulation accuracy of a CMX transmit is determined by the down-converter feedback path. A worst-case value of —30dB is guaranteed. Note that a different loop-filter might be required for the kHz and kHz channels. The data will appear in the grayed-out data box. What can I do to ensure a stable carrier leakage when I enable the RF detector?
The effect is shown in Table 1 below:. 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.
CMX998 – Cartesian Feedback Loop Transmitter
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 dBc, which is considered more than adequate for most applications.
For clarification, the relevant change is: Can you help explain how the instability cmmx998 on the CMX operates and how it can be used? 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. If the loop becomes unstable due to phase inaccuracies the feedback loop will tend to spill energy out-of band.
The instability detector comprises a high-pass filter followed by a peak-detector circuit and this combination indicates the presence of this high frequency energy. As phase error increases, cmx99 instability detector will show a worsening level of out-band energy. The CMX instability detector cannot detect lead or lag error as it works on a simple baseband signal.
CMX Datasheet(PDF) – CML Microcircuits
The error signal produced by the instability detector should be accessed for a particular design and an appropriate threshold set. The CMX includes gain adjustment to make threshold setting easier. If the loop is set up degrees out of phase the loop will oscillate and will cmmx998 produce a maximum level carrier.
As this is effectively a stable oscillating condition the instability detector will not detect this operating state. The instability detector is designed to detect minor phase variations and resultant instability following initial phase correction. Typical changes are variations in antenna VSWR and thermal effects. Such effects are unlikely to cause a phase shift as large as degrees.
If instability is detected then normal procedure is to power down the transmitter. If a cmx98 supports dynamic loop phase calibration then an instability detector event normally triggers loop re-calibration.
The measurements include the effects of the non-ideal PA that is corrected by the Cartesian loop. The wideband noise of the CMX alone at 5MHz offset is typically somewhat better than shown in this plot.
The degradation is due to the gain-expansion caused by the datsaheet correction for the non-ideal PA. I am looking to develop a high quality non-constant envelope transmitter and am looking to improve the linearity of my current design. This effect can be avoided by using Dtaasheet to bias the input signal rather than using a resistor network tied to 3.
Cmx989 Single Ended and Differential modes are shown. Are there any datasheett aspects of power-up or down sequence of the EV that I should be aware of? 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. The PA device is not protected cmx99 enabling this device without the load may irreparably dame the device.
There is a preferred method of powering down the EV to also avoid damage to the power amplifier PA.
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 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 CMX down-converter before powering down the PA. Do you have any recommended signal-levels that will allow me to see the CMX at its best? Using a Cartesian transmitter in TDMA systems can be challenging when supporting multiple modulation formats.
This App Note discusses these issues using the DE in a worked example. These scripts require the following evaluation boards: It is important to read the included readme.
These scripts can be easily modified to support other Block Types. Three scripts for evaluating performance of a multi-mode modem using the DE Datasheets CMX Datasheet rev Technical Portal No additional information available.
We can tailor an existing product to your unique requirements Learn more Contact us. There are three CMX internal registers that are key for this discussion: The effect is shown in Table 1 below: 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.
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