HP E1429A manual Chapter Understanding the HP E1429 Digitizer

To get the 10 μs sample period (100 kHz rate), the digitizer processor divides the reference by 200 (N):

20 MHz / N = 20 MHz / 200 = 100 kHz 1 / 100 kHz = 10 μs

Oversampling The Nyquist criteria states that the sample rate must be at least 2 times the maximum frequency component of the input signal. To limit aliasing, it is recommended that a sample rate 4 times or greater the maximum frequency component be used. For example, to oversample at a frequency four times or 10 times the maximum frequency component, the sample period is computed as:

<period > = 1 / 4(fc)

<period > = 1 / 10(fc)

The minimum number of samples (i.e. <size > or TRIGger:STARt:COUNt) to take is determined by:

sample count = signal period (fundamental) / [1 / 4(fc)] or [1 / 10(fc)]

Dual Rate Sampling TheHP E1429 digitizer’s dual rate sampling feature allows pre-arm readings and post-arm readings to occur at different sample rates. The following trigger sources specify dual rate sampling:

∙DECLtrg - VXIbus trigger line ECLTRG0 paces pre-arm readings, ECLTRG1 paces post arm readings.

∙DEXTernal - input port "Ext 1" paces pre-arm readings, input port "Ext 2" paces post-arm readings.

∙DTIMer - TRIGger[:STARt]:TIMer1 paces pre-arm readings, TRIGger[:STARt]:TIMer2 paces post-arm readings.

When the dual rate sampling trigger source is DTIM, one sample rate must equal the reference period. For example, if the digitizer’s 20 MHz oscillator is used, one sample rate must be 50 ns. Similarly, if VXI CLK10 is used, one sample rate must be 100 ns (1/10 MHz). If the reference source for DTIM is ECLT0, ECLT1, or EXT2, one rate must be equal to the reference period. The other rate can be any other valid sample rate given the reference source.

When the dual rate sampling trigger source is DECL or DEXT, both sampling rates can be any periods you choose.

Chapter 3 Understanding the HP E1429 Digitizer 123