[SI-LIST] Re: Unforeseen resonance
- From: "Lewandowski, Bob" <blewandowski@xxxxxxxxxxxxxxxxxxxx>
- To: <jeff.loyer@xxxxxxxxx>,"Signal Integrity Mailing List" <si-list@xxxxxxxxxxxxx>
- Date: Tue, 10 Dec 2002 15:33:17 -0600
Jeff,
Can you give a little more detail about what you are measuring? If it's
a real board you may have coupling to an adjacent trace that is
effectively open circuited at both ends, and is half wave resonant at
3.54 GHz. Does the simulation show the same effect?
---Bob Lewandowski
-----Original Message-----
From: Loyer, Jeff
Sent: Tue 12/10/2002 9:57 AM
To: Signal Integrity Mailing List
Cc:
Subject: [SI-LIST] Unforeseen resonance
While measuring and simulating long coupled T-lines, I came
across a =
"resonance" (sudden increase in S21 magnitude loss) at a much
higher =
frequency than I expected. In the simulation below, a 13.655"
coupled =
T-line with a Tp of ~160pS/in has a resonance for S21 at
3.54GHz.
By my calculations, 13.655" at 160pS/in is ~2.2nS, or 457MHz.
Does =
anybody know where a resonance at 3.54GHz would come from?
Spice deck:
Simulation of Long Coupled Microstrip=20
.param coupled_L=3D13.655
=20
.options INGOLD=3D1
.AC Lin 800 30K 16G
.PRINT AC S21(DB) S11(DB) S21(P) S11(P)
.NET V(N_port2) V_ACsrc ROUT=3D50 RIN=3D50
V_ACsrc N_port1 0 ac=3D1 dc=3D0
R_VNAterm N_port2 0 50Meg
* Coupled Length
W_coupled_active N_port1 N_port3 0 N_port2 N_port4 0=20
+ RLGCfile=3Drlc_5n5mil_coupled.txt N=3D2 =
L=3D'.0254*(coupled_L)'
* Terminate port 3 to 50ohms
R_port3_term N_port3 0 R=3D50
* Terminate port 4 to 50ohms
R_port4_term N_port4 0 R=3D50
.END
RLGC_file contents:
*** From To Ze Zo Se So FXtalk BXtalk
*** 1 1 49.08 - 1.91 - - -
*** 1 2 56.27 41.46 1.97 1.84 0.068 0.152
*** 2 2 49.08 - 1.91 - - -
***************************************************************
****************************
* Number of Conductors =3D 2 *
****************************
2
**************
*** Lo (H/m) *
**************
3.075197e-007 =20
5.673228e-008 3.077165e-007 =20
**************
*** Co (F/m) *
**************
1.304724e-010 =20
-1.543307e-011 1.305906e-010 =20
*****************
*** Ro (ohms/m) *
*****************
5.585039e+000 =20
0.000000e+000 5.585039e+000 =20
********************
*** Go (Siemens/m) *
********************
0.000000e+000 =20
0.000000e+000 0.000000e+000 =20
*************************
*** Rs (ohms/(m*Hz^.5)) *
*************************
2.111018e-003 =20
0.000000e+000 2.123407e-003 =20
*******************
*** Gd (S/(m*Hz)) *
*******************
1.475806e-011 =20
-1.745687e-012 1.476994e-011 =20
Jeff Loyer
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