Design Article
Supercapacitors enhance audio quality and power in mobile phones - Pt 2
Pierre Mars, VP of Applications Engineering, CAP-XX Ltd.
6/14/2007 7:49 AM EDT
Editor's note: Part 1 of this series may be read at Supercapacitors enhance audio quality and power in mobile phones
Test Results
To test the audio improvement with a supercapacitor we created two test setups:
For the case without supercapacitor (Fig 1), we connected the audio amps to a Li Ion battery @ 3.7V and drove a pair of 8Ω speakers.
For the case with supercapacitor (Fig 2), we connected the battery to the input of a buck-boost converter, with input current limited to 250mA and with the output set to 5V. We placed a 0.55F supercapacitor with 85mΩ ESR across the output of the buck-boost and connected it to supply inputs of the audio amps as shown in Fig 2. We also drove 2 pairs of 8Ω speakers, 1 pair across each audio amp, halving the output impedance and further doubling the total speaker power.
High power bass bursts representing a bass beat and
A network poll while listening to music, which we represented as a 1KHz tone, in order to make any improvements from the supercapacitor obvious. The speaker power in Figs 3 " 6 is the total speaker power for both stereo channels.
Bass Beat
We created a 100Hz bass beat that lasted approximately 120msecs and repeated every 0.5secs. Fig 3 shows speaker power and battery current for the standard configuration of most cell phones, and Fig 4 shows the same information for the configuration with a supercapacitor and 4 speakers.
Test Results
To test the audio improvement with a supercapacitor we created two test setups:
Test Setup 1: Class D Audio Amps
In the first test setup we built the circuits as shown in Fig 1 & in Fig 2, using a pair of TPA2023D1 to provide the stereo audio channels:
With this setup, we tested:
Bass Beat
We created a 100Hz bass beat that lasted approximately 120msecs and repeated every 0.5secs. Fig 3 shows speaker power and battery current for the standard configuration of most cell phones, and Fig 4 shows the same information for the configuration with a supercapacitor and 4 speakers.
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