C_IDC

	C_IDC Coplanar Interdigitated Capacitor Parameters Notes Equivalent Circuit
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Coplanar Interdigitated Capacitor

The C_IDC module represents an interdigitated capacitor between center conductor of two coplanar lines. WF is the width of fingers, SF the distance between the fingers and LF the length of the fingers. The dimensions of connected lines at ports are defined using data items addressed by C_ LTYP1 and C_LTYP2. L1 and L2 are the length of coplanar lines connected at ports.

Parameters

Parameter	Description	Range of Usage
L1	Length of transmission line connected to the port 1
L2	Length of transmission line connected to the port 2
WF	Width of fingers	n/2.DL(n=1,2,3,...)
SF	Slot between fingers	n/2.DL(n=1,2,3,...)
LF	Length of fingers (LF > SF)	n/2.DL(n=2,3,4,...)
NF	Number of fingers	2,3,4,...
S	Slot between ground and fingers	n/2.DL(n=1,2,3,...)
G	Gap between ground and feed line	n/2.DL(n=1,2,3,...)
WL	Width of feed line	n/2.DL(n=1,2,3,...)
IDCLEVEL	Identification of metal level of the interdigital section	1 or 2 (DEFAULT Foundry)
C_LTYP1	ID of coplanar transmission line applied at ports 1
C_LTYP2	ID of coplanar transmission line applied at ports 2
C_SUB	ID of coplanar substrate definition
C_GRID	ID of simulation control data
TEMP	ID of element temperature definition used for noise computation

Notes

In the current version, the same C_LTYP is applied at both ports for the simulation (C_LTYP2 = C_LTYP1).
A negative value for L1 or L2 can be meaningful during the simulation. In such cases, the automated layout generation works incorrectly and the generated layout has to be edited manually. The minimum value for L1 and L2 depends on the metal layer oversize in the currently selected C_LAYER. In case of DEFAULT foundry, L1 and L2 should be greater than or equal to max(|cond_os|, |cond2_os|).
LF should always be greater than SF.
NF is the number of fingers and has to be an integer number. The minimum value for NF is 2. Note that for odd numbers of NF, the number of fingers connected to port one is greater than the number of fingers connected to port 2.
S is the slot between fingers and the ground planes. This parameter influences the parasitic electric field to the ground (parameters C_p1 and C_p2 in equivalent circuit).
WL is the length of feed lines connected to the fingers.
The parameter IDCLEVEL indicates the metal level used for the interdigitated capacitor. The only valid value for this parameter in the DEFAULT foundry is 1 or 2. If IDCLEVEL and CEN_MET of connected lines are different, an inter metal via is automatically included at the ports. In this case the length of connected lines must at least via_lo in C_LAYER.
If L1 and L2 in selected C_GRID are not set to –1 or –2 (auto sizing), the minimum values for L1 and L2 are:

L1_min= max(NF.WF+(NF-1)SF+2S+8DL

L2_min=LF+SF+2WL+2G+8DL

Equivalent Circuit

For the modeling of the C_IDC element, a broadband network is used. The electrical coupling betwwen the fingers is represented by the capacitance Cs, whereas the parasitic electric field to the ground is considered by the shunt capacitances Cp1 and Cp2. An ideal transformer (inductances L1 and L2 as well as mutual indactance M) is uesd for the modeling of the magnetic coupling between the fingers. Frequency dependent resistances (R1 and R2) represents the metal losses of the fingers.

The traveling wave effects along the fingers is taken into account. As a result, there is no limitation due to the length of fingers. The equivalent circuit parameters are derived from quasi-static FD-calculations. The connected line at ports are modeled as C_LIN elements and are represented by their characteristic mpedances ZL1, ZL2 and phase constants b1, b2. There is no limitation due to the length of connected lines (L1 and L2).