EMI Suppression Filters (EMC and Noise Suppression)ToF Noise Suppression (3)

Contents

6Confirming the effects of ferrite bead insertion

We confirmed the change in noise suppression effectiveness with and without insertion of ferrite beads.
We also checked to determine if there were any effects on voltage or current waveforms, aside from noise suppression effectiveness.
We checked for changes in ripple noise to confirm effectiveness in reducing noise flowing to the power supply side on transmitter power line ① in the figure below, and we checked for changes in transient response to confirm absence of harmful effects on the voltage waveform at VCSEL power input ②.
We also checked for changes in the current waveform flowing to the VCSEL.

Method of confirming noise suppression effectiveness

Voltage① → Confirmation based on ripple noise
Voltage② → Confirmation based on transient response
Current → Confirmation based on current wave form

7Confirmation of effectiveness of ferrite bead insertion – ripple noise

We can see that inserting BLE18PK100SN1 ferrite beads into the power line as shown in the figure below reduced ripple at location ① to about 1/5 the previous level.
We confirmed that insertion of ferrite beads substantially reduces ripple noise.

Effectiveness of ferrite beads in reducing ripple noise

8Confirmation of effectiveness of ferrite bead insertion – transient response

On the other hand, it would be unacceptable if ferrite bead insertion had a harmful effect on the voltage supplied to the VCSEL.
We checked the transient response before and after insertion of ferrite beads and confirmed that there was no reduction in wave height due to ferrite bead insertion.
Inserting ferrite beads resulted in no observable harmful effect on the operation of the circuit.

Effect of ferrite bead insertion on transient response

9Confirmation of effectiveness of ferrite bead insertion – VCSEL current waveform

Next, we checked the waveform of the current flowing to the VCSEL.
A comparison of current waveforms before and after ferrite bead insertion shows almost no difference.
Thus, we confirmed no harmful effects due to reduction in wave height following ferrite bead insertion.

Effect of ferrite bead insertion on VCSEL current waveform

10Summary

  • Steep, large current pulses flow to the ToF transmitter, and these current pulses tend to generate significant ripple noise in the power line.
  • Inserting ferrite beads can reduce noise without harmful effects on voltage or current waveforms or on transient response.
  • We recommend the following ferrite bead products for noise suppression from the standpoint of large-current support and compactness.
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Recommended ferrite bead products
Part No. Search inventory L dimension W dimension Impedance
(@100MHz)
Rated current
(at 85℃)
Rated current
(at 125℃)
1.6mm 0.8mm 10Ω 6A 3.5A
1.6mm 0.8mm 8A 5A
1.0mm 0.5mm 20Ω 3.8A 2.35A