Datasheet parameters

AN4071

14/27

Doc ID 022939 Rev 1

Measurement

To keep low source impedance and prevent from parasitic oscillation during switching, a 100

source is used. A 50

Ω resistor minimizes the effect of input pin capacitance and avoids

signal reflection on the line matching the impedance at inputs of the comparator with the

It is necessary to define exactly the measurement conditions, especially the load

loading at the comparator output including loading capacitor, oscilloscope probe capacity

and parasitic capacity of the PCB track.

Figure 16.

Many pulse generators, despite great performance in the time-base, are not able to provide

accurate signal amplitude, especially for low output voltage. Generating 5 mV overdrive may

be a problem because such a value is often below the generator accuracy. Therefore, for

small overdrive measurement, it is more suitable to place a 50

Ω attenuator (divider bridge),

instead of a single 50

Ω resistor, and increase the generator amplitude. In this way, a good

amplitude accuracy can be obtained with low overdrive values.

High speed signal processing

For high-speed signal applications, more attention (at PCB level) must be paid to: proper low

resistive grounding, short tracks and quality SMD capacitors having low ESR. Bypass

line. Each real capacitor has resonant frequency where its impedance reaches the lowest

value. If the input signal frequency is far from the resonant frequency, impedance strongly

increases and the capacitor loses bypassing capability. Placing different capacitors with

different resonant frequencies therefore allows a wide frequency bandwidth to be covered.