JP2012170032A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor device capable of automatically determining the type of an input signal and outputting an output signal with optimum characteristics for the type from a common output terminal.SOLUTION: A semiconductor device according to an embodiment comprises: a variable gain amplifier 1 capable of varying gain; and a counter 2 configured to measure a frequency of an input signal SIG. A switching module 3 switches between outputting the input signal SIG to an output terminal OUT via the variable gain amplifier 1 and outputting the input signal SIG as it is, according to the frequency of the input signal SIG. In the semiconductor device, when the input signal SIG is output to the output terminal OUT via the variable gain amplifier 1, an output destination impedance determination module 4 determines the magnitude of input impedance of a device connected to the output terminal OUT, and a gain adjustment module 5 adjusts gain of the variable gain amplifier 1 according to the magnitude of the input impedance of the device connected to the output terminal OUT.

Description

  Embodiments described herein relate generally to a semiconductor device.

  In portable devices such as mobile phones and portable audio players, with the progress of miniaturization and multi-functionality, it is necessary to arrange a large number of connectors on the main body. For this reason, while downsizing of connectors has been promoted, different types of signals that have been conventionally transmitted by dedicated connectors are also transmitted using a single connector. As one of them, the USB connector for digital signal transmission is also used to transmit an audio signal that is an analog signal.

  Therefore, a semiconductor device that is mounted on a portable device that uses such a dual-purpose connector and outputs a signal of a different type via this dual-purpose connector outputs an output signal according to the counterpart device connected to this dual-purpose connector. It is necessary to switch.

  For example, when the USB connector is also used, it is necessary to output an audio signal if the device connected to the USB connector is a sound reproduction device such as a speaker or an earphone, and to output a USB signal if the device is a USB memory.

  Conventionally, such output signal switching is performed by controlling a semiconductor switch connected to an output terminal by a CPU or the like.

  Among the required characteristics of the semiconductor switch for switching the output, particularly important characteristics are the on-resistance and the switch capacitance. For example, when the on-resistance of a semiconductor switch through which an audio signal passes is large, there arises a problem that the audio signal cannot be transmitted. Further, in the case of a USB signal, there is a problem that normal data transmission cannot be performed when the on-capacitance of a semiconductor switch that passes during data transmission or the switch-off capacity of a semiconductor switch connected in parallel to the transmission path is large.

  Also, when outputting an audio signal, the input impedance of a speaker or earphone connected to the USB connector varies depending on the product, such as 8Ω or 16Ω. Therefore, if the current output from the USB connector is constant, there arises a problem that the reproduction volume varies greatly due to the difference in input impedance between the speaker and the earphone.

JP 2007-116243 A

  Accordingly, the problem to be solved by the present invention is to provide a semiconductor device that can automatically determine the type of an input signal and output an output signal having characteristics optimal for the type from a common output terminal. is there.

  The semiconductor device according to the embodiment includes a variable gain amplifier capable of changing a gain, and a frequency measurement unit that measures the frequency of the input signal, and the switching unit changes the input signal according to the frequency of the input signal. Is output to the output terminal via the variable gain amplifier or to the output terminal as it is. Further, in this semiconductor device, when the input signal is output to the output terminal via the variable gain amplifier, the output destination impedance determination means determines the level of the input impedance of the device connected to the output terminal. The gain adjustment unit adjusts the gain of the variable gain amplifier according to the level of the input impedance.

1 is a block diagram showing an example of the configuration of a semiconductor device according to a first embodiment of the present invention. Operation | movement explanatory drawing of the switching part of the semiconductor device of 1st Embodiment when an input signal is an audio signal. Operation | movement explanatory drawing of the switch part of the semiconductor device of 1st Embodiment when an input signal is a USB signal. The block diagram which shows the example of a structure of the semiconductor device which concerns on the 2nd Embodiment of this invention. Operation | movement explanatory drawing of the switching part of the semiconductor device of 2nd Embodiment when an input signal is an audio signal. Operation | movement explanatory drawing of the switching part of the semiconductor device of 2nd Embodiment when an input signal is a USB signal.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will not be repeated.

(First embodiment)
FIG. 1 is a block diagram showing an example of the configuration of the semiconductor device according to the first embodiment of the present invention.

  The semiconductor device of this embodiment includes a variable gain amplifier 1 that can change the gain, a counter 2 that measures the frequency of the input signal SIG, and an input signal SIG that is variable according to the frequency of the input signal. The switching unit 3 for switching between output to the output terminal OUT or the output terminal OUT as it is, and the output terminal when the input signal SIG is output to the output terminal OUT via the variable gain amplifier 1 An output destination impedance determination unit 4 that determines the level of the input impedance of the device connected to OUT, and a gain adjustment unit that adjusts the gain of the variable gain amplifier 1 according to the level of the input impedance of the device connected to the output terminal OUT 5 is provided.

  The switching unit 3 in the present embodiment includes a switch SW1 that switches whether to output the input signal SIG to the output terminal OUT, and a switch SW2 that switches whether to supply the power supply voltage VDD to the variable gain amplifier 1 or to make the switch SW1 conductive. And a switch SW3 for switching whether or not to input the input signal SIG to the variable gain amplifier 1, a switch SW4 for switching whether or not to output the output of the variable gain amplifier 1 to the output terminal OUT, and the measurement result of the counter 2 And a switch control unit 31 that controls switching of the switches SW2 to SW4.

  Here, an example of a switch using a MOS transistor is shown as the switch SW1, and the switch SW1 conducts when the power supply voltage VDD is applied to the gate terminal via the switch SW2.

  The switch control unit 31 controls switching of the switches SW <b> 2 to SW <b> 4 according to the measurement result of the counter 2. The frequency of a general audio signal is 20 Hz to 20 kHz, and the frequency of a general USB signal is 1.5 MHz to 480 MHz. Accordingly, by setting the determination threshold between 20 Hz and 1.5 MHz, the switch control unit 31 determines whether the input signal is an audio signal or a USB signal, and based on the determination result, switches SW2 to SW4. Switch. 2 and 3 show how the switches SW2 to SW4 are switched.

  FIG. 2 shows how the switches SW2 to SW4 are switched when the input signal SIG is an audio signal.

  When the switch control unit 31 determines that the input signal SIG is an audio signal, the switch control unit 31 switches the switch SW2 to supply the power supply voltage VDD to the variable gain amplifier 1 and switches the input signal SIG to be input to the variable gain amplifier 1. The switch SW4 is switched so that the output of the variable gain amplifier 1 is output to the output terminal OUT.

  Thus, the input audio signal is input to the variable gain amplifier 1 and amplified, and the amplified audio signal is output to the output terminal OUT.

  At this time, the output impedance determination unit 4 determines the level of the input impedance of the device connected to the output terminal OUT. In the case of outputting an audio signal, a speaker or an earphone is connected to the output terminal OUT. Generally, the input impedance of a speaker or earphone is 8Ω or 16Ω. Therefore, the output destination impedance determination unit 4 observes the value of the current flowing through the output terminal OUT and determines the level of the input destination input impedance.

  In response to the determination result of the output destination impedance determination unit 4, the gain adjustment unit 5 controls the gain of the variable gain amplifier 1.

  That is, when the determination result of the output destination impedance determination unit 4 is “high”, the gain adjustment unit 5 reduces the gain of the variable gain amplifier 1 and the determination result of the output destination impedance determination unit 4 is “low”. In some cases, the gain of the variable gain amplifier 1 is increased.

  Thereby, when the input impedance of the output destination is high, the current flowing to the output destination is small, and when the input impedance of the output destination is low, the current flowing to the output destination is large. As a result, the voltage generated in the output destination speaker or earphone is constant regardless of the input impedance, and the audio signal can be reproduced at an optimum volume.

  FIG. 3 shows how the switches SW2 to SW4 are switched when the input signal SIG is a USB signal.

  When the switch control unit 31 determines that the input signal is a USB signal, the switch control unit 31 switches the switch SW2 so as to apply the power supply voltage VDD to the gate terminal of the switch SW1, and does not input the input signal SIG to the variable gain amplifier 1. The switch is switched so that the output of the variable gain amplifier 1 is not output to the output terminal OUT.

  As a result, the input USB signal is output to the output terminal OUT via the switch SW1. That is, in the case of a high-frequency signal such as a USB signal, output with a low switch capacity is possible.

  According to this embodiment, the counter 2 measures the frequency of the input signal SIG, and based on the result, the switch control unit 31 determines whether the input signal SIG is a low frequency audio signal or a high frequency USB signal. And the switches SW2 to SW4 are switched to automatically switch the signal path of the input signal SIG to the output terminal OUT. As a result, an output signal having characteristics optimal for the signal type of the input signal SIG can be output from the common output terminal OUT without switching the signal path from the outside. At this time, if the input signal SIG is an audio signal, an audio signal that can be reproduced at an optimum volume can be transmitted regardless of the input impedance of the output destination. If the input signal SIG is a USB signal, The output signal can be transmitted with the switch capacity.

(Second Embodiment)
FIG. 4 is a block diagram showing an example of the configuration of the semiconductor device according to the second embodiment of the present invention.

  In the semiconductor device of this embodiment, the switch SW3 and the switch SW4 are deleted from the circuit of the semiconductor device of the first embodiment. That is, in this embodiment, the input signal SIG is directly input to the variable gain amplifier 1, and the output of the variable gain amplifier 1 is directly output to the output terminal OUT.

  The switching unit 3A of the semiconductor device of the present embodiment switches the switch SW1 for switching whether or not to output the input signal SIG to the output terminal OUT, and whether to supply the power supply voltage VDD to the variable gain amplifier 1 or to make the switch SW1 conductive. The switch control unit 31 </ b> A controls switching of the switch SW <b> 2 according to the measurement result of the counter 2.

  FIG. 5 shows how the switch SW2 is switched when the input signal SIG is an audio signal.

  When the switch control unit 31A determines that the input signal SIG is an audio signal, the switch control unit 31A switches the switch SW2 so as to supply the power supply voltage VDD to the variable gain amplifier 1. As a result, the input audio signal is amplified by the variable gain amplifier 1, and the amplified audio signal is output to the output terminal OUT.

  Thus, in this embodiment, when the input signal SIG is an audio signal, no switch is inserted in the signal path. Therefore, as compared with the first embodiment, an audio signal can be transmitted with a low on-resistance because the on-resistance of the switch is not added.

  FIG. 6 shows how the switch SW2 is switched when the input signal SIG is a USB signal.

  When the switch control unit 31A determines that the input signal is a USB signal, the switch control unit 31A switches the switch SW2 to apply the power supply voltage VDD to the gate terminal of the switch SW1. As a result, the input USB signal is output to the output terminal OUT via the switch SW1.

  Normally, the capacitance of the variable gain amplifier 1 is sufficiently smaller than the switch capacitances of the switches SW3 and SW4 used in the first embodiment, so that the capacitance connected in parallel to the switch SW1 is reduced as compared with the first embodiment. For this reason, in this embodiment, USB signals can be transmitted with a further low switch capacity.

  According to the present embodiment, when the input signal SIG is an audio signal, signal transmission with a lower on-resistance is possible, and when the input signal is a USB signal, a lower switch capacitance can be achieved. Signal transmission is possible.

  According to the semiconductor device of at least one embodiment described above, it is possible to automatically determine the type of the input signal and output the output signal having the optimum characteristics for the type from the common output terminal.

  Moreover, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 Variable gain amplifier 2 Counter 3, 3A switching part 4 Output destination impedance determination part 5 Gain adjustment part 31, 31A Switch control part SW1-SW4 switch

Claims (6)

A variable gain amplifier capable of changing the gain;
A frequency measurement unit for measuring the frequency of the input signal;
According to the frequency of the input signal, the switching means for switching the input signal to be output to the output terminal via the variable gain amplifier or to be output to the output terminal as it is,
When outputting the input signal to the output terminal via the variable gain amplifier, output destination impedance determination means for determining the level of the input impedance of the device connected to the output terminal;
A semiconductor device comprising: a gain adjusting unit that adjusts a gain of the variable gain amplifier according to a level of the input impedance. The switching means is
A first switch for switching whether to output the input signal to the output terminal;
A second switch that switches between supplying a power supply voltage to the variable gain amplifier or making the first switch conductive;
A third switch for switching whether to input the input signal to the variable gain amplifier;
A fourth switch for switching whether or not to output the output of the variable gain amplifier to the output terminal;
The semiconductor device according to claim 1, further comprising: a switch control unit that controls switching of the second to fourth switches according to a frequency of the input signal. The switch controller is
When the frequency of the input signal is low, the second switch is switched to supply a power supply voltage to the variable gain amplifier, and the third switch is input to input the input signal to the variable gain amplifier. Switching, switching the fourth switch to output the output of the variable gain amplifier to the output terminal,
When the frequency of the input signal is high frequency, the second switch is switched so as to make the first switch conductive, the third switch is switched so as not to input the input signal to the variable gain amplifier, The semiconductor device according to claim 2, wherein the fourth switch is switched so that an output of a variable gain amplifier is not output to the output terminal. The switching means is
A first switch for switching whether to output the input signal to the output terminal;
A second switch that switches between supplying a power supply voltage to the variable gain amplifier or making the first switch conductive;
The semiconductor device according to claim 1, further comprising: a switch control unit that controls switching of the second switch in accordance with a frequency of the input signal. The switch controller is
When the frequency of the input signal is low, the second switch is switched to supply a power supply voltage to the variable gain amplifier,
5. The semiconductor device according to claim 4, wherein when the frequency of the input signal is high, the second switch is switched so that the first switch is turned on. The gain adjusting unit is
When the input impedance is high, lower the gain of the variable gain amplifier,
6. The semiconductor device according to claim 1, wherein when the input impedance is low, the gain of the variable gain amplifier is increased.

Images