UM8511 Datasheet, PDF (4/7 Pages) Union Semiconductor, Inc. – 8 Line ESD/EMI Protections for Color LCD Interfaces

UM8511
Applications Information
Insertion Loss
Insertion Loss (IL) is used to describe the transmission coefficient between two points in a circuit
often described in terms of dB. When examining S parameters, S21 is often described as insertion loss.
Insertion Loss and S21 will be used interchangeably from here on out. The insertion loss of a circuit
with VOUT and VIN would be expressed as
IL = S₂₁(dB) = 20log (V_OUT/V_IN )
The setup for measuring insertion loss in a 50 Ω system is shown in Figure 3. It will be analyzed in a
50Ω environment, so the source impedance and load impedance is 50 Ω. The transfer functions then
can be analyzed in terms of insertion loss (S21).
Fig 3 Test Conditions: Source Impedence = 50Ω
Load Impedence = 50Ω
Input Power = 0dBm
Cut Off Frequency
Cut off Frequency is the frequency at which the signal strength is 3.0 dB less than it is Pass Band 3.0
dB of attenuation equates to half the original signal power. The Pass Band is the range of frequencies
that are allowed to “pass” through a filter with minimal attenuation. For our purposes it starts from
DC and ends at the cut off frequency.
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