Agilent Technologies E8267C PSG Manual de usuario descargar pdf (Pagina 13)

Accurate and meaningful test results – A series of multitone signals with random phase

sets are required to adequately simulate real world operating conditions. Random phase

sets can be generated directly from the instrument front panel or remotely using the GPIB

or LAN interface.

Save time – Spend less time setting up the desired test stimulus and more time making

measurements. To optimize testing with multiple phase sets, use the waveform sequencing

capability of the baseband generator to minimize the waveform switching time.

Reduce cost – Use a single signal generator to produce a multitone test signals that

traditionally required multiple analog signal generators and a signal combiner.

Issues with vector technique

Available power – When using a single signal generator to produce a multitone signal,

the total power available from the signal generator is divided into each enabled tone

based on the relative tone power settings. As a result, there is less power available per

tone as compared to the traditional analog approach. Also, as the number of tones

increases, the peak-to-average ratio of the composite signal increases. This must be

taken into account in both the signal generator and with any amplifiers used to increase

the composite signal power. The signal generator output power level should be reduced

to account for the peak power of the multitone signal. This will ensure that additional

distortion is not introduced by overdriving the signal generator. When using external

amplifiers, the same concern applies. In addition, a linear amplifier with a flat passband

that is wide enough to accommodate the multitone signal should be used to avoid

introducing additional distortion to the signal prior to the input of the DUT.

Carrier feed through – Because an I/Q modulator is employed to create the desired

multitone signal, a small amount of carrier feed through is present when an even number

of tones are enabled. (With an odd number of tones, there is always a tone placed at the

carrier frequency.) A high level of carrier feed through is undesirable since it will result in

intermodulation products at one-half the tone spacing interval rather than at intervals

equal to the tone spacing. Although carrier feed through cannot be eliminated, it can be

minimized through a simple iterative procedure that optimizes the I and Q gain offsets.

For additional information on this procedure, refer to I/Q adjustment procedure in the

multitone section of the E8267C PSG User’s Guide.

Images – Images arise when tones are enabled in a non-symmetrical pattern with

respect to the carrier frequency. Images occur as a result of the I and Q signals being

slightly out of quadrature at the input of the I/Q modulator. When non-symmetrical tone

patterns are used, images can be minimized with slight adjustments to the quadrature

skew setting in the I/Q adjustments menu.

Relative tone spacing – Tone spacing is limited to the 80 MHz RF modulation bandwidth

of the internal baseband generator. The maximum relative tone spacing is calculated by

dividing 80 MHz by (N-1), where N equals the number of tones. The maximum relative

tone spacing calculation assumes that all tones are enabled. If individual tones are

disabled, the increased tone spacing is a multiple of the maximum relative tone spacing.

For example, if 5 tones are enabled, the maximum relative tone spacing is 20 MHz. If tone

2 is then disabled, the tone spacing between tones 1 and 3 is then 40 MHz. Relative tone

spacing can be set down to 100 Hz, however tone spacing cannot arbitrarily be set on a

tone-by-tone basis.

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