LM339LVDR datasheet(32/71 Pages) TI2

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7.2.9 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 7-18. 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 7-19 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 7-19. Pulse Slicer Waveforms

7.3 Power Supply Recommendations

Due to the fast output edges, it is critical to have bypass capacitors on the supply pin to prevent supply ringing

and false triggers and oscillations. Bypass the supply directly at each device with a low ESR 0.1 µF ceramic

bypass capacitor directly between VCC pin and ground pins. Narrow, peak currents will be drawn during the

output transition time, particularly for the push-pull output device. These narrow pulses can cause un-bypassed

TL331LV, TL391LV, LM393LV, LM339LV

SNOSDA4D – JUNE 2020 – REVISED NOVEMBER 2023

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LM339LVDR Datasheet(PDF) 32 Page - Texas Instruments

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