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Wide Band Digitally Modulated Signal Measurements

RI Measurement Approach
S Parameter Detection Hardware
True RMS Noise Detector
Digital Modulation Signal Generator
Auxiliary Source Fast Power Control

Measurement Process

The Noise measurement hardware provides high performance wide band digitally modulated signal measurements very quickly (less than 35 msec) with the true root mean squared (RMS) noise power detection hardware. The user selects the RF frequency of the RF Stimulus Source (AUX 1), sets the DMSG output power to maximum, and controls the auxiliary power in the Source 1/2 Combiner Matrix Module to quickly adjust the desired RF power level. The auxiliary power control is a solid-state variable pin attenuator designed to facilitate fast power sweeps for precise DUT POUT setting. When utilizing any Power amplification on digitally modulated signals like CDMA, significant head room must be maintained to ensure that there is minimal degradation in the output waveform. RI recommends an minimum of 10dB head room from the desired Pout.

Typical CDMA Wide Band Digitally Modulated Signal

Adjacent Channel Power Ratio (ACPR) or Adjacent Channel Leakage Ratio ( ACLR ) measurements are similar to Spur measurements previously discussed. The true RMS Noise Power Detector and the Spurs can be measured using either the S Parameter detection hardware or the True RMS Noise detector (depending on the DUT's requirements). The system measures the signal level of both the transmitted fundamental tone and adjacent channel (at the output of the DUT) by quickly tuning the system LO for the receiver to measure the fundamental signal, making a power measurement, then tuning to the adjacent signal and making another power measurement. The actual order in which these measurements are performed is controlled by the test plan optimizer. The difference in the signal levels is the ACPR performance and the units displayed are dBc in a specific bandwidth.

Large Cassini with 4 Source Combiner (RI8566A) for Modulated Source

The diagram shown is a typical auxillary Digitally Modulated Source measurement configuration available only with the Large Infrastructure (RI8557A) and 4 Source Combiner module (RI8566A). The system will use this module in the RF Matrix to send the Auxiliary source input signal through a special high speed pin attenuation and then optional power amplifier through the Source 1 output path to the Test Head Source 1 Input port. An alternative could be to apply Source 2 (as a jammer tone for example) and route both signals through the RF broadband power combiner, then send the combined signal to the Test Head Source 1 input port.

Measurement Configuration for Wide Band modulated signals

Modulated signals measurements by the System Receiver is the same as the measurement process for Noise Power measurements. The system LO frequency is tuned for the fundamental stimulus signal and is downconverted to a 21.4 MHz IF. The IF signal is conditioned (attenuated, filtered or amplified) and sent to the True RMS Noise Power detector. The resulting signal is routed through the high speed sample and hold circuits and the high accuracy A to D converter digitizes the sampled RMS power and sends the digitized data over the RIFL bus to the System controller. This process will be repeated for as may of the other signals as desired, then the System Software calculates the relative level of the product with respect to the level of the fundamental signal and reports that values in dBc.

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