Remember, the decoupling cap on the inductor - to the power is a 0.1uf & a 1 or 10uf,
with such a large capacitance on the inductor, also since it is a power connection
with a very low impedance, even 8 trace swings is plentiful.
You are obviously correct if the capacitive load on the inductor was 10pf, you would
need 20-30 swings to completely remove frequencies above 75Mhz.
I've use the Burr-Brown PCM300x codecs with excellent results under these
circumstances. The described RF I believe is in the 24 Mhz range for the serial data
buss for the audio. If you have severe digital noise on your digital supply, a larger
printed inductor may be necessary, but since we are talking about an any high
frequency cut there is an incredible play range for the printed inductor.
_____________
Brian Guralnick
----- Original Message -----
From: "Ian Wilson" <[EMAIL PROTECTED]>
To: "Protel EDA Forum" <[EMAIL PROTECTED]>
Sent: Tuesday, June 26, 2001 6:36 PM
Subject: Re: [PEDA] Ground Planes Connection
| On 03:46 PM 26/06/2001 -0400, Brian Guralnick said:
| >----- Original Message -----
| >From: "Abd ul-Rahman Lomax" <[EMAIL PROTECTED]>
| >To: "Protel EDA Forum" <[EMAIL PROTECTED]>
| >Sent: Tuesday, June 26, 2001 1:55 PM
| >Subject: Re: [PEDA] Ground Planes Connection
| >|
| >| To connect at DC or low frequencies while isolating RF, an inductor would
| >| be used.
| >|
| >
| >It's under these circumstances where I've sucessfully used printed inductors.
| >
| >_____________
| >Brian Guralnick
|
|
| Though I would hazard a guess that you are operating at higher freqs than
| the original poster. They mentioned FM, assuming normal FM bands, I would
| assume printed inductors get unreasonably large, and discrete have
| reasonable size, Q, SRF etc at the 88-108 MHz band these days. (Not that
| one would want high Q for supply/ground coupling anyway and would usually
| deliberately degrade Q to prevent noise peaking.)
|
| Or do you find that you do get useful inductance from printed inductors at
| 100MHz-odd freqs? What sort of inductance can be achieved in reasonable
| space using printed inductors and standard line/spacing of say 8/8 or 6/6?
|
| Ian
|
|
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