Capacitor
MLCCs: An Alternative solution, for Smartphone applications, instead of Tantalum Capacitor
Tantalum capacitors are often used as the capacitor connected to the power line of PA (= Power Amplifier) for GSM on smart phones. In this report, we evaluate replacing the tantalum capacitor (Ta-Cap) with a ceramic capacitor.
1. Target capacitor
We purchased a smartphone and evaluated it. The circuit of the battery line, which is the analysis of our own, is shown in the figure below. A Ta-Cap is connected near the power line of the PA for GSM.
2. Proposal of replacement
The proposal is illustrated below. We selected the low acoustic noise Ceramic capacitor "ZRB series" as replacement. As you can see, the mounting space is reduced by 50%.
Proposal
C1: Ta-Cap 100uF/1206size × 1pcs → Low acoustic noise ceramic capacitor 22uF/6.3V/0603size × 2pcs
3. Evaluation for replacement
We measured the following properties before and after replacement.
1) Communication characteristics
The value of the capacitor that is connected to the PA power line affects signal quality. Therefore, it is necessary to test the communication characteristics.
2) Voltage fluctuation
If the impedance of the power line changes, noise will change. Therefore, it is necessary to test the power line voltage fluctuations of the PA.
3) Acoustic evaluation
The PA for GSM is operated by a burst audible frequency (217Hz) cycle. Therefore, an evaluation of acoustic noise is required.
4. Communication characteristics and voltage fluctuation
Communication characteristics and voltage fluctuation were tested by the measurement system below.
Communication characteristics (1)
The communication characteristics meet the standard for GSM.
Communication characteristics (2)
The communication characteristics meet the standard for GSM.
Voltage fluctuation (1)
The noise of power line is reduced 7–8%.
Voltage fluctuation (2)
The noise of power line is reduced 14–22%.
5. Evaluation of acoustic noise
Acoustic noise is measured as sound pressure level (SPL) by the measurement system below.
SPL is equal to the initial. (There is no significant difference.)
6. Summary of evaluation
We evaluated replacing the Ta-Cap that is connected to the power line of the PA for GSM with a ceramic capacitor. In the evaluation, we tested (1) the communication characteristics, (2) the voltage fluctuation, and (3) acoustic noise.
1) Communication characteristics
The communication characteristics are equal to the initial and meet the standard for GSM.
2) Voltage fluctuation
Voltage fluctuation is reduced 7–22%.
3) Evaluation of acoustic noise
Acoustic noise level is equal to the initial.
7. Merits of using ceramic capacitors
Advantages of replacing the Ta-Cap with a ceramic capacitor
Impedance characteristics of Ta-Cap 100uF vs. ceramic capacitor 22uF
Ceramic capacitors have low ESR and low ESL characteristics. Therefore, the impedance of a ceramic capacitor (22uF/6.3V/0603size) is smaller than that of a Ta-Cap (100uF/6.3V/1206size) over 100kHz range. Thus, the ceramic capacitor has a better noise suppression effect at a high-frequency range.
Ripple current – Self heating characteristics
Temp. rise level is lower than Ta-Cap. due to low ESR.
Breakdown Voltage Characteristics
Ceramic capacitors have high breakdown voltage.
8. Summary
We demonstrated the evaluation result of replacing the Ta-Cap with a ceramic capacitor, and the benefits of using a ceramic capacitor.
Evaluation for replacement
- Voltage fluctuation is reduced 7–22%.
- The communication characteristics are equal to the initial and meet the standard for GSM.
- Acoustic noise level is equal to the initial.
Benefits of using a ceramic capacitor
- Ceramic capacitors have good performance for noise suppression because the ESR and ESL of ceramic capacitors are lower than Ta-Cap.
- Ceramic capacitor has low temperature rise performance because the ESR of ceramic capacitors is lower than Ta-Cap.
- Breakdown voltage of ceramic capacitors is higher than Ta-Cap.
Proposal
C1: Ta-Cap 100uF/1206size × 1pcs → Low acoustic noise Ceramic capacitor 22uF/6.3V/0603size × 2pcs
Replacement parts number: ZRB18AR60J226ME01
Contact your local Murata sales rep for further support.
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