________________________________________________________________________

http://www.union-ic.com

Rev.04 Jul.2012

5/11

UM4601/4611/8601/8611

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

The setup for measuring insertion loss in a 50 Ω system is shown in the figure below. 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).

Test Conditions: Source Impedance = 50Ω

Load Impedance = 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.

Device Connection

The UM4601/UM4611/UM8601/UM8611 is comprised of identical circuits consisting of a low

pass filter for EMI suppression and dual TVS diodes for ESD protection. The device is in an 8-pin

DFN and 16-pin DFN package. Electrical connection is made to all the pins located at the bottom

of the device. A center tab serves as the ground connection. The device has a flow through design

for easy layout. All path lengths should be kept as short as possible to minimize the effects of

parasitic inductance in the board traces.