RF InductorProposal of the Noise Suppression Technology in the PA and Power Line

-Example of Using Power Inductors for Chokes-

Selection of filters to improve signal integrity in wired connection evaluations

In order to improve the signal integrity in wired connection evaluations, it is necessary to suppress the low frequency noise (switching noise) of a DC/DC converter.
The insertion loss of each filter condition is shown in the following. Due to the frequency characteristics of the insertion loss, it is effective to insert the LQW15CN series or BLM15PX121 immediately after the output LC, to suppress the switching noise (1MHz-10MHz) of a DC/DC converter.
The inductance value and capacitance of the output LC in this evaluation are assumed for a DC/DC converter with a switching frequency of 6MHz.

Selection of filters to improve signal integrity in wired connection evaluations
Selection of filters to improve signal integrity in wired connection evaluations
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Condition 1 Condition 2 Condition 3
Condition 1
Condition 2
Condition 3
Condition 4 Condition 5 Condition 6
Condition 4
Condition 5
Condition 6

Relationship between Filter Insertion Loss and ACLR

The relationship between the insertion loss (@6 MHz) of each filter condition 1-6 shown above and the evaluation results of the ACLR (L1) in each filter condition is shown using an evaluation board.
The switching frequency of the DC/DC converter on the evaluation board was 6MHz in this test.

Relationship between Filter Insertion Loss and ACLR
Relationship between Filter Insertion Loss and ACLR

The correlation between the insertion loss of the filter including the output LC of the DC/DC converter and the bypass capacitor of the PA, and the evaluation results of the ACLR can be confirmed.

Relationship between Noise Level of Power Lines and ACLR

The relationship between the switching noise level (@6MHz) of the DC/DC converter which is superimposed in the power lines in each filter condition 1-6 shown above, and the evaluation results of the ACLR (L1) in each filter condition is shown using an evaluation board.

Relationship between Filter Insertion Loss and ACLR
Relationship between Filter Insertion Loss and ACLR

The correlation between the switching noise level of the DC/DC converter which is superimposed in the power lines in each filter condition, and the evaluation results of the ACLR in each filter condition can be confirmed.

Notes for DC Resistance of Filters

When inserting filters in power lines in series, there are cases where the Rdc (DC resistance) of the filter may affect the RF signal integrity.

  • When a resistance component exists in PA power lines in series, the saturation input power becomes lower.
  • The output power becomes insufficient, which demands higher input power.
  • The operating point will shift to a point with larger distortion.

 When the Rdc (DC resistance) of the filter becomes larger, the input voltage of the PA drops due to the gain characteristics of PA, and distortion may occur in the RF signal. The effect on the power conversion efficiency also becomes larger. Pay attention to the Rdc (DC resistance) of the filter.

Notes for DC Resistance of Filters

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