Abstract: This circuit automatically turns off the speaker driver when no audio signal is detected to save battery energy in a mobile phone.
The AutoShutdown™ circuit shown in Figure 1 describes the transient characteristics of a phone call. When the circuit detects that the call is interrupted, it puts the speaker amplifier into a low-power shutdown mode to save battery energy and extend the call time. When the call is resumed, the audio amplifier will start immediately to avoid losing voice information.
Figure 1. This circuit saves battery power by automatically shutting down the speaker driver when there is no audio signal.
The main consumption of the mobile phone battery is the RF power amplifier and the speaker (Class AB speaker amplifier). Under ideal conditions, it consumes 353mARMS when driving an 8Ω speaker with 1W power. When there is no audio signal input, it also consumes milliamps of current. For this reason, most speaker driver ICs have a shutdown mode to reduce the current consumption of the chip when the driver is not in use. The
quiescent current of the circuit is very different from the current in shutdown mode. For example, U1 in Figure 1 consumes 5mA of quiescent current when there is no signal input, but when U1 is placed in shutdown mode, it only consumes 10nA of current. In Figure 1, the power consumption of the entire circuit can be reduced from 4.7mA to 22µA when the input audio signal is below the preset threshold at a defined time interval.
The window comparator (U2 or U3) compares the input signal with a preset reference voltage proportional to VCC. R6 and R7 bias the input audio signal to the middle point of the comparator window, VCC/2. R3 to R5 set the reference voltage of the window comparator. The high and low thresholds are calculated as follows: The difference between the thresholds
(VHIGH - VLOW) is set to prevent noise signals from turning on the speaker amplifier. The
open-drain output of the comparator is connected to the SHDN input of U1. When the peak-to-peak value of the audio input exceeds the window range set by R3 to R5, the open-drain output automatically controls the speaker driver to turn on, and the VSHDN voltage is pulled to ground potential (as shown in Figure 2). When the input audio signal is within the window, both outputs are turned off, and C6 and the pull-up resistor R8 slow the rise of the VSHDN voltage to the threshold that turns off U1.
Figure 2. The shutdown signal (VSHDN) in Figure 1 is driven low when the input exceeds a preset threshold. The large time constant created by C6 and R8 prevents the audio signal from being switched on and off unnecessarily.
Wake-up from the shutdown state is very fast because C6 discharges directly to ground through the open-drain output of the comparator. The fast turn-on ensures that no speech information is lost (Figure 3).
Figure 3. The speaker in Figure 1 turns off quickly after the input signal is removed.
Reference address：The speaker amplifier can be automatically shut down to effectively save power consumption of the mobile phone
|
Figure 1. This circuit saves battery power by automatically shutting down the speaker driver when there is no audio signal.
The main consumption of the mobile phone battery is the RF power amplifier and the speaker (Class AB speaker amplifier). Under ideal conditions, it consumes 353mARMS when driving an 8Ω speaker with 1W power. When there is no audio signal input, it also consumes milliamps of current. For this reason, most speaker driver ICs have a shutdown mode to reduce the current consumption of the chip when the driver is not in use. The
quiescent current of the circuit is very different from the current in shutdown mode. For example, U1 in Figure 1 consumes 5mA of quiescent current when there is no signal input, but when U1 is placed in shutdown mode, it only consumes 10nA of current. In Figure 1, the power consumption of the entire circuit can be reduced from 4.7mA to 22µA when the input audio signal is below the preset threshold at a defined time interval.
The window comparator (U2 or U3) compares the input signal with a preset reference voltage proportional to VCC. R6 and R7 bias the input audio signal to the middle point of the comparator window, VCC/2. R3 to R5 set the reference voltage of the window comparator. The high and low thresholds are calculated as follows: The difference between the thresholds
(VHIGH - VLOW) is set to prevent noise signals from turning on the speaker amplifier. The
open-drain output of the comparator is connected to the SHDN input of U1. When the peak-to-peak value of the audio input exceeds the window range set by R3 to R5, the open-drain output automatically controls the speaker driver to turn on, and the VSHDN voltage is pulled to ground potential (as shown in Figure 2). When the input audio signal is within the window, both outputs are turned off, and C6 and the pull-up resistor R8 slow the rise of the VSHDN voltage to the threshold that turns off U1.
Figure 2. The shutdown signal (VSHDN) in Figure 1 is driven low when the input exceeds a preset threshold. The large time constant created by C6 and R8 prevents the audio signal from being switched on and off unnecessarily.
Wake-up from the shutdown state is very fast because C6 discharges directly to ground through the open-drain output of the comparator. The fast turn-on ensures that no speech information is lost (Figure 3).
Figure 3. The speaker in Figure 1 turns off quickly after the input signal is removed.
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Recommended ReadingLatest update time:2024-11-16 14:43
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