Agilent Technologies E1441A user service Table C-1, for AM, 624for FM, Appendix C

The table below shows the function generator's carrier frequency and burst count limitations (for sine, square and arbitrary waveforms only).

Table C-1.

Carrier Frequency	Minimum
	Burst Count
10 mHz to 1 MHz	1
>1 MHz to 2 MHz	2
>2 MHz to 3 MHz	3
>3 MHz to 4 MHz	4
>4 MHz to 5 MHz	5

Internal Modulation Source Internally, the function generator incorporates a second, lower speed and lower resolution DDS arbitrary waveform generator to produce the modulating signal independent of the carrier signal. Internal modulation waveshapes range in length from 2,048 points to 4,096 points. User-defined arbitrary waveforms are automatically expanded or compressed in length as needed to fit within the required modulation waveform constraints. Linear interpolation is performed on user-defined arbitrary waveforms while the lengths of standard waveshapes are varied by decimation. Due to the modulation sample rate and waveform size limitations, the best case modulation signal frequency accuracy is approximately 0.05% of setting.

Unlike the main signal output discussed previously, modulation waveshapes are sampled using a variable “point clock” to sample data loaded in modulation waveform RAM. Internally, the modulation point clock (C) and modulation waveform length are automatically adjusted to produce the modulation signal frequency desired. For frequencies greater than C/2048, all modulation shapes are sampled up to the maximum modulating frequency. A new modulation waveform is computed and loaded into modulation RAM each time the modulation type, modulation waveshape, or modulation frequency is changed. Data in standard arbitrary waveform memory is not affected by modulation signal changes (data is expanded or compressed and loaded directly into separate modulation RAM following computation). No expansion or compression is performed on the modulation waveform data for certain modulation frequencies.

You can use the equations on the next page to determine specific waveform lengths and modulation frequencies when more precise control is needed. Normally, you should not have to perform these calculations.

The function generator incorporates an internal 8-bit (± 7 bits peak) digital-to-analog converter (DAC) to create an analog copy of the modulation signal for amplitude modulation (AM). This signal is internally applied to a conventional four-quadrant analog multiplier circuit to achieve amplitude modulation. Similarly, the generator uses digital signal processing to combine the carrier and modulation signals for frequency modulation (FM). The FM modulation signal maintains 12-bit resolution for frequency values.

The following equations and example describe the capabilities and limitations of the Agilent E1441A's internal modulation signal generator.

Parameter Definitions:
Maximum Point Clock (C) = 5 MSa/ s	(for AM)
	1.25 MSa/ s (for FM)

Modulation Prescaler (S) = integer numbers (truncated) from 1, 2, 3, ... 220

Constant (k) = 4,900 (for AM)

624(for FM)

Modulation Frequency (F) = 10 mHz to 20 kHz (for AM)

10 mHz to 10 kHz (for FM)

Points (P) = values from 2,048 to 4,096,

Appendix C Agilent E1441A Function Generator Tutorial 161