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Issue #206 September
2007
Smart Power
An Intelligent Power Supply for Embedded Systems
by Alexander Popov & Jordan Popov
Start | Hardware | Software | Calibration | Voltage Presets | Slowly Rising Voltage | Slowly Falling Voltage | Short Time Test | Periodcal Linear Voltage | Periodical Voltage Drops | Future Development | Sources & PDF
PERIODICAL VOLTAGE DROPS
The waveform generated by this preset has even more harmonics than the periodical linear one (see Photo 7). Thus, it is a test for the power supply filtering of the entire circuit, especially useful for noise-sensitive audio amplifiers, such as those for microphones or guitars.
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| Photo 7—This is a test for the power supply filtering of the entire circuit. It is especially useful for noise-sensitive audio amplifiers, such as those used for microphones and guitars. |
A popular module in embedded systems is a GSM/GPRS modem, sometimes used for voice communication. Due to the time-division multiplexing in the GSM network, the modem drains current unequally, but periodically in time. The frequency is about 216 Hz and can be very annoying. It is heard when a GSM phone is placed near an FM radio tuner or active PC speakers. The peak current consumed by the modem is about 2 A, which causes voltage drops in the traces, thus introducing noise across power supply lines. Noise is easily transferred to the sensitive audio circuits if they are not routed properly. To test how the circuit reacts to this, the periodical voltage drops preset can be used, configuring it with parameters to simulate an active GSM modem. By altering the voltage drop, the power supply rejection ratio of the audio amplifiers can be evaluated.
The preset is configured with three parameters: T_DROP, the voltage drop duration, T_PER, the period of repetition, and V_DROP, the voltage to drop to.
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