Mobile device with a headphone amplifier

Abstract

A mobile device (100) is provided with a headphone jack (102) suitable for connecting headphones (200) and a headphone amplifier (101) designed to provide sufficient amplification for a reproduced audio signal. The headphone amplifier (101) includes a level measurement unit (120) designed to detect the level of an incoming signal (LS, RS) to be amplified. The headphone amplifier (101) also includes an impedance estimation unit (130) designed to determine the impedance of a connected headphone (200) based on the level measurement by the level measurement unit (120) and on the current measurement at the output of a power supply unit (140).The impedance estimation unit (130) is designed to estimate the impedance of a connected headphone (200) and to initiate a change in the supply voltage if the currently applied supply voltage leads to a reduction in the efficiency of the power supply for the headphone (200).

Description

[0001] The present invention relates to mobile devices having a headphone amplifier.

[0002] Mobile devices such as a bodypack or a beltpack, which have a headphone amplifier to which headphones are connected, typically have a rechargeable battery as a power supply.

[0003] It is therefore an object of the present invention to provide a mobile device with a headphone amplifier which enables a longer battery life.

[0004] This object is achieved by a mobile device according to claim 1 and by a method for controlling a mobile device according to claim 4.

[0005] Thus, a mobile device with a headphone amplifier and a headphone jack is provided. The headphone amplifier has a level measuring unit for measuring the level of an incoming signal. The headphone amplifier further has a current measuring unit, which serves to detect a current measurement at the output of a power supply. Furthermore, the headphone amplifier has an impedance estimation unit, which performs an impedance estimation based on the detected level and the detected current in order to obtain a suitable output voltage for the headphones. Thus, by detecting the impedance of the headphones, the power supply for the headphones can be automatically adjusted accordingly. This leads to increased efficiency of the mobile device, since the mobile device can operate with a variable output voltage for the headphones. The output voltage for the headphones can thus be adjusted to the respective impedance of the headphones.

[0006] According to one aspect of the invention, instead of one amplifier for the headphone, the headphone amplifier can be provided with two amplifiers (one amplifier for the left and one amplifier for the right).

[0007] Thus, the invention also relates to a mobile device with a headphone jack for connecting headphones and a headphone amplifier that enables sufficient amplification for an audio signal to be reproduced. The headphone amplifier has a first amplifier for a left signal component of the signal to be reproduced and a second amplifier for a right signal component of the signal to be reproduced. The first and second amplifiers each have a level measuring unit designed to detect a level of an incoming left or right signal component to be amplified, and an impedance estimation unit designed to detect an impedance of a left or right transducer of a connected headphone based on the level measurement by the level measuring unit and based on a current measurement at the output of a power supply unit.The impedance estimation unit is configured to estimate an impedance of a left or right transducer of the connected headphone and to initiate a change in the supply voltage if the currently applied supply voltage leads to a reduction in the efficiency of the power supply for the left or right transducer of the headphone.

[0008] Further embodiments of the invention are the subject of the subclaims.

[0009] Advantages and embodiments of the invention are explained in more detail below with reference to the drawing. Fig. 1 shows a block diagram of a mobile device, Fig. 2 shows a flow chart for controlling the mobile device, Fig. 3A to 3C show the influence of different headphone impedances on the supply voltage for a headphone, Fig. 4A to 4C each show a graph illustrating the influence of different headphone impedances on the current, Fig. 5A to 5C each show a graph illustrating the effect of different headphone impedances on performance, and Fig. Figures 6A to 6C each show a graph illustrating the effects of different impedances on the efficiency of the mobile device.

[0010] Fig. 1 shows a block diagram of a mobile device. The mobile device 100 has a headphone amplifier 101 and a headphone jack 102 to which a pair of headphones 200 can be connected. The mobile device 100 has a processor 110 with a level measuring unit 120 and an impedance estimation unit 130. The level measuring unit 120 receives an audio signal (LS left, RS right). Optionally, an input for a manual trigger MF can be provided. The mobile device 100 further has a power supply 140, a digital / analog converter 150, an amplifier 160, and a CON unit 170. A pair of headphones 200 can be connected to the unit 170. The unit 170 serves to detect the insertion of a plug. This plug detection information PD is output to the level measuring unit 120.The impedance estimation unit 130 receives the detected level and a current measurement from a current measuring unit 180 and outputs a selected voltage VS to the power supply 140.

[0011] The processor 110 can receive two input signals, namely left LS and right RS, and output these signals to the digital-to-analog converter 150. A current measurement unit 180 is provided at the output of the power supply 140, which outputs a current measurement CM to the impedance estimation unit 130.

[0012] The level measuring unit 120 can output a control signal C for starting and stopping to the current measuring unit 180.

[0013] Fig. Figure 2 shows a flow diagram for controlling the mobile device. Initialization of the impedance measurement can occur in step S10. Initialization can occur when a connector is detected in step 3, when the start of an audio signal is detected in step S2, or when a device is started in step S1.

[0014] In step S20, a check is made to determine whether the audio peak is above a threshold. If this is not the case, the flow returns to the input of step S20. If the audio peak is above a threshold, the flow continues to step S30, where a level measurement and a current measurement are performed. In step S40, the current measurement is performed, and the result is output to an impedance estimation unit in step S70. In step S50, a level measurement is performed, and in step S60, a check is made to determine whether the audio level is above a threshold. If this is not the case, the flow returns to step S20. If, however, the audio level is above a threshold, the flow continues to step S70, where an impedance estimation is performed. The flow then continues to step S80, where the voltage supply is reduced to the required value. The method then ends in step S100.

[0015] An example of an impedance measurement is a measurement of the current of the amplifier's positive supply voltage by comparing the average current consumption over a measurement period with the average value of the positive signal components during the measurement period. The measurement period can be, for example, 100 to 1000 ms.

[0016] To measure the headphone load impedance, a DC voltage can be applied to a series resistor, and the resulting voltage across the resistor's voltage divider and the load are measured. With dynamic transducers, this can produce sufficiently accurate results. However, with other transducers, such a measurement can lead to inaccuracies.

[0017] According to one example, other methods for measuring an impedance of the headphone may also be performed.

[0018] According to one aspect, and in particular with regard to steps S20 and S60, monitoring is performed to determine whether a sufficiently strong audio signal is present. It should be noted that the dynamic range of the current measurement is significantly lower than the dynamic range of a real audio signal. However, in order to realize a cost-effective current measurement, the measurement result can only be evaluated when the audio signal is sufficiently strong, as the current measurement otherwise runs the risk of being lost in the noise.

[0019] The determination of whether a sufficient signal-to-noise ratio (SNR) is present is based on the fact that, for example, a measurement can be started on suspicion if at least one short event above a certain threshold has been reached. This assumes that a sufficient average signal level will be present throughout the entire measurement period. For very short peaks in the audio signal without a significant average level, the average signal-to-noise ratio of the measurement would be insufficient and could lead to a falsified measurement. For example, this result may not be determined until the end of the measurement period. In such a case, the measurement must be discarded.

[0020] Fig. 3A to 3C show the influence of different headphone impedances on the voltage.

[0021] Fig. Figures 4A to 4C each show a graph illustrating the influence of different headphone impedances on the current.

[0022] Fig. Figures 5A to 5C each show a graph illustrating the effect of different headphone impedances on performance.

[0023] Fig. Figures 6A to 6C each show a graph illustrating the effects of different impedances on the efficiency of the mobile device.

[0024] The Fig. The graphs shown in Figures 3 to 6 are based on calculations using the following equations: VSUPPLY,MIN=2×POUT,RMS×RLOAD+VHR ηMAX=POUT,RMSVSUPPLY,MIN×(POUT,RMSRLOAD×8π+IQ) η=POUT,RMSVSUPPLY×(POUT,RMSRLOAD×8π+IQ)

[0025] Other parameters that can have an influence here are the headroom of the amplifier between maximum output level and supply voltage (output rail-to-rail distance V HR (for example 0.5 volts) and the quiescent current of the amplifier I Q (e.g., 5 mA). These calculations apply to sine signals.

[0026] In the Fig. 3A to 6C, a 300 ohm load is compared with an 8 ohm load at the same supply voltage. In both cases, a power of 100 mW is applied to the load. For the 300 ohm load, this results in a supply voltage of ± 8.2 volts. This leads, as in Fig. 6A results in an efficiency of 56.6%. If the supply voltage is maintained at a low load, the efficiency at a load of 8 ohms is only 11.5% as shown in Fig. 6B. After successful impedance measurement, the supply voltage can then be reduced to ± 1.8 volts without loss of audio quality (as shown in the Fig. 3C, Fig. 4C, Fig. 5C and Fig. 6C). This leads to the efficiency increasing again to 53.6% (see Fig. 6C).

[0027] According to one example, the preamplifier can detect the use of mono jack plugs (tip-sleeve TS) instead of stereo jack plugs (tip-ring-sleeve TRS). This results in the load being applied only to the left channel, while the right channel is short-circuited. This, in turn, can lead to a lower-impedance total load being detected than actually present. To prevent this, the right signal can be muted in a second pass so that the impedance estimation is performed only on the left channel. Connector detection can thus be extended to include mono detection.

Claims

[1] Mobile device (100), with a headphone jack (102) adapted to connect a headphone (200), and a headphone amplifier (101) which is designed to provide sufficient amplification for an audio signal to be reproduced, where the headphone amplifier (101) a level measuring unit (120) which is designed to detect a level of an incoming signal (LS, RS) to be amplified, an impedance estimation unit (130) which is designed to detect an impedance of a connected headphone (200) on the basis of the level measurement by the level measuring unit (120) and on the basis of a current measurement at the output of a power supply unit (140), wherein the impedance estimation unit (130) is configured to estimate an impedance of a connected headphone (200) and to initiate a change in the supply voltage if the currently applied supply voltage leads to a reduction in an efficiency of the power supply for the headphone (200). [2] Mobile device (100) according to claim 1, wherein a comparison of a detected audio peak with a threshold is performed and if the audio peak is greater than the threshold, then the level measurement is initiated by the level measuring unit (120) and the current measurement is initiated by the current measuring unit (180). [3] Mobile device (100) according to claim 1 or 2, wherein the level measurement is checked to see whether it is above a threshold value, wherein if the level measurement is above a threshold value, the impedance estimation is initiated by the impedance estimation unit (130). [4] Mobile device (100), with a headphone jack (102) adapted to connect a headphone (200), and a headphone amplifier (101) which is designed to provide sufficient amplification for an audio signal to be reproduced, where the headphone amplifier (101) a first amplifier for a left signal component of the signal to be reproduced and a second amplifier for a right signal component of the signal to be reproduced, wherein the first and second amplifiers each have a level measuring unit (120) which is designed to detect a level of an incoming left or right signal component (LS, RS) to be amplified, and an impedance estimation unit (130) which is designed to detect an impedance of a left or right transducer of a connected headphone (200) on the basis of the level measurement by the level measuring unit (120) and on the basis of a current measurement at the output of a power supply unit (140), wherein the impedance estimation unit (130) is configured to estimate an impedance of a left or right transducer of the connected headphone (200) and to initiate a change in the supply voltage if the currently applied supply voltage leads to a reduction in an efficiency of the energy supply for the left or right transducer of the headphone (200). [5] Method for controlling a mobile device (100) having a headphone amplifier (101) and a headphone jack (102), comprising the steps: Carrying out a level measurement by a level measuring unit (120), Carrying out a current measurement by a current measuring unit (180), Performing an impedance estimation (S70) based on the level measurement and the current measurement, and Reduce or increase the supply voltage for the headphones (200) according to the estimated impedance.

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