LM339LVDR datasheet(32/63 Pages) TI1

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8.2.9 Pulse Slicer

A Pulse Slicer is a variation of the Zero Crossing Detector and is used to detect the zero crossings on an input

signal with a varying baseline level. This circuit works best with symmetrical waveforms. The RC network of R1

and C1 establishes an mean reference voltage VREF, which tracks the mean amplitude of the VIN signal. The

noninverting input is directly connected to VREF through R2. R2 and R3 are used to produce hysteresis to keep

transitions free of spurious toggles. The time constant is a tradeoff between long-term symmetry and response

time to changes in amplitude.

If the waveform is data, it is recommended that the data be encoded in NRZ (Non-Return to Zero) format

to maintain proper average baseline. Asymmetrical inputs may suffer from timing distortions caused by the

changing VREF average voltage.

10M

470 k

0.01 F

Output

VREF

VIN

VPU

RPU

Figure 8-18. Pulse Slicer

For this design, follow these design requirements:

• The RC constant value (R2 and C1) must support the targeted data rate in order to maintain a valid tripping

threshold.

• The hysteresis introduced with R2 and R43 helps to avoid spurious output toggles.

Figure 8-19 shows the results of a 9600 baud data signal riding on a varying baseline.

OUT

REF

1.8 V

1.2 V

4.0 V

0.0 V

1.61 V

1.58 V

Time

0.0

200.0 u

400.0 u

600.0 u

800.0 u

Figure 8-19. Pulse Slicer Waveforms

TL331LV, TL391LV, LM393LV, LM339LV

SNOSDA4C – JUNE 2020 – REVISED MARCH 2023

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