LM567C: detection bandwidth for ±200mVin, fo=1.8kHz, C2=0.1uF, C3=0.47uF

Hung Ching Hsu

Expert 3086 points

Part Number: LM567C

Hi Team,

My customer is asking the detection bandwidth for following condition. Could you kindly help?

・Input voltage : DC offset voltage=2V, amplitude=±200mV.

・detection frequency(fo)=1.8kHz

・Loop Filter cap(C2)=0.1uF

・output filter cap(C3)=0.47uF

First, is it correct to calculate Vrms by Vrms = amplitude / √2 ?

And can you share the calculation and result for detection bandwidth?

I see there are two formula depends on Vrms> 200mV or < 200mV, but I'm not sure which should I use in this case.

Thanks.

Regards,

over 4 years ago

0 Jennifer Bernal over 4 years ago

TI__Genius 16585 points

Hi Jo,

Vrms is calculated by either Vp / √2 or Vpp / 2√2. Then for +/-200mV, Vrms ≈ 141 mV, which falls under the Operation With Vi < 200m – VRMS category. Use this equation to get the bandwidth:

BW = 1070√(141m / (1.8k * 0.1u)) ≈ 29.9k => Get in % of fo: 1.8k/29.9k = 6%

Regards,
Jennifer

0 Hung Ching Hsu over 4 years ago in reply to Jennifer Bernal

TI__Expert 3086 points

Hi Jennifer,

Thanks for the detailed explanation!

Let me ask one more question.

The result of BW is 6% and fo is 1.8kHz, will the range be 1.8k±3% or 1.8k±6%?

Thanks.

Regards,

0 Jennifer Bernal over 4 years ago in reply to Hung Ching Hsu

TI__Genius 16585 points

Hi Jo,

I apologize for the delay. I believe it is the absolute frequency (+/- 3%) but I can't confirm because it's an old device and there is little expertise left.

Regards,

Jennifer

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LM567C: detection bandwidth for ±200mVin, fo=1.8kHz, C2=0.1uF, C3=0.47uF