JP2005292618A - Stroboscopic circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stroboscopic circuit capable of increasing communication quality, regarding a portable communication (calls) apparatus with a camera function. <P>SOLUTION: Regarding the stroboscopic circuit for controlling the light emission of a stroboscope loaded on the portable communication apparatus with camera functions, the circuit is constituted so that a power supply voltage may be increased up to a prescribed pressure by a separately excited booster circuit 2, and a driving frequency generated by the booster circuit 2 can be set as a frequency which does not interrupt the transmitting/receiving processing at communication. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a strobe circuit, and more particularly, to a strobe circuit that performs light emission control of a strobe provided in a portable communication device with a camera.

  In recent years, mobile phones exemplified as mobile communication devices have become smaller and more multifunctional, and in particular, mobile phones having a camera function have become extremely popular. A conventional strobe circuit provided in this type of camera-equipped mobile phone is generally constituted by a booster circuit that boosts a power supply voltage such as a battery, a light emission control circuit, a discharge tube such as a xenon tube, and the like. Here, the boosting operation in the conventional strobe circuit will be described with reference to FIG.

  In FIG. 4A, a supply voltage (for example, 3 to 4 V) from a battery or the like is boosted to a high voltage by the booster circuit 7. This boosted voltage is rectified by the rectifier diode 3, and as a result, charges are accumulated in the main capacitor 4 (charging of the main capacitor). Then, the electric charge of the main capacitor 4 is supplied to a discharge tube (not shown) such as a xenon tube by a light emission control circuit (not shown), so that the discharge tube emits light (strobe light emission).

  The booster circuit 7 includes an oscillation transistor, an oscillation transformer, and the like (not shown) therein. Oscillation is started when a current flows through the oscillation transistor, and the oscillation transformer generates electricity at this oscillation frequency. This is a self-excited booster circuit that boosts the voltage.

  Such a self-excited booster circuit is widely used in this type of strobe circuit because it has a reduced number of parts and can be manufactured at low cost. However, this method has the property that the oscillation (driving) frequency changes over a wide range of several tens to 200 kHz depending on the state of charge of the main capacitor, and the frequency is not constant.

  By the way, at the time of transmission / reception of the cellular phone, the transmission / reception signal is once converted into a signal of an intermediate (IF) frequency (about 400 to 450 kHz), and transmission / reception processing is performed. If frequency noise is mixed in the IF frequency signal, the transmission / reception processing may be hindered, and communication failure may occur. As described above, since the drive frequency of the booster circuit is in the range of several tens to 200 kHz, it corresponds to the noise and may cause a communication failure. In such a case, a smoothing (filter) circuit 8 comprising an inductor 9 and a capacitor 10 as shown in FIG. 4B is inserted between the power source + and the booster circuit 7 to stabilize the drive frequency at a predetermined frequency. Possible countermeasures (FIG. 5 is a diagram showing a power drop waveform at point A in FIG. 4 (a), FIG. 5 (a) shows a case where there is no filter, and FIG. 5 (b) shows a case where a filter is inserted. ing.). However, in order to take this measure, a large inductor is required as the inductor 9 of the filter circuit 8, which is not desirable for a mobile phone with a high demand for downsizing.

On the other hand, by separating the strobe device and the transmission / reception circuit with an electromagnetic shield frame, the noise is attenuated or charging processing in the strobe device is prohibited during a call so as not to generate a driving frequency. A countermeasure plan such as the above is proposed in Patent Document 1.
JP 2001-320622 A

  However, as described above, even if a strobe device or the like that is a driving frequency (noise) generation source is covered with an electromagnetic shield, there is a possibility that the influence on the transmission / reception processing due to noise cannot be prevented. In addition, if charging during a call is prohibited, inconvenience may occur when shooting immediately after the call.

  Therefore, the present invention has been made to solve the above-described problems of the prior art, and by stabilizing the drive frequency generated in the booster circuit to a desired frequency, the IF frequency signal is not affected, and communication failure An object of the present invention is to provide a strobe circuit that can prevent the above-described problem.

  A strobe circuit according to the present invention is a strobe circuit that controls light emission of a strobe provided in a portable communication device with a camera function, boosts a power supply voltage to a predetermined voltage by a boost circuit of another excitation system, and oscillates from the boost circuit. The drive frequency to be set can be set to a frequency that does not hinder transmission / reception processing during communication.

  The strobe circuit having the above configuration boosts a voltage supplied from a power supply voltage such as a battery to a predetermined voltage (a voltage for charging a main capacitor with energy (charge) for causing a discharge tube such as a xenon tube to emit light). As a circuit for this purpose, a separately excited booster circuit is employed.

  The separately-excited booster circuit oscillates an oscillation element (transistor or the like) provided inside based on an oscillation control signal from the outside (for example, CPU), and can adjust the drive frequency to a desired frequency. It becomes possible. Therefore, if the frequency is adjusted (set) so that the IF frequency of the transmission / reception signal is not affected as much as possible, the transmission / reception process can be performed without any trouble, and the occurrence of the communication failure can be prevented.

  In addition, the drive frequency oscillated from the booster circuit can be set to a frequency farthest from an integral multiple of an intermediate (IF) frequency of transmission / reception signals during communication or a frequency of 1 / integer. In this way, the drive frequency of the booster circuit can be moved away from an integer multiple of the IF frequency or a fraction of an integer that tends to affect the transmission / reception signal, and the occurrence of communication failure can be prevented more reliably.

  This drive frequency is preferably set to a frequency farthest from an integer multiple or a fraction of an integer of the IF frequency of the transmission / reception signal.

  Further, when a filter (smoothing) circuit is provided between the power supply voltage input unit and the booster circuit, further noise reduction (stabilization of drive frequency) can be achieved.

  In this case, by adjusting the drive frequency to be higher (for example, higher than the IF frequency), the inductor inside the filter circuit can be reduced in size, and there is no problem in inserting the filter circuit.

  As described above, the strobe circuit of the present invention employs a separately excited booster circuit, and the drive frequency oscillated by the booster circuit can be controlled to a desired frequency, so that the drive frequency becomes the IF frequency of the transmission / reception signal. By adjusting the frequency to have as little influence as possible, communication failure can be prevented and communication (call) quality can be improved.

  Hereinafter, strobe circuits according to embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a schematic configuration of a strobe circuit according to the present embodiment.

  The strobe circuit shown in FIG. 1 is used for controlling the strobe emission of a camera-equipped mobile phone, and has a feature in the step-up operation of the power supply voltage for charging the strobe emission. (Light emission control processing, light emission processing, etc.) is substantially the same as a conventional strobe circuit. Therefore, in the strobe circuit of FIG. 1, illustration of a light emission control circuit and a discharge tube such as a xenon tube is omitted.

  In FIG. 1, a filter circuit 1 includes an inductor 5 and a capacitor 6 and smoothes a supply current. FIG. 2 is a power supply drop waveform diagram at point A during charging of the strobe circuit according to the present embodiment. Compared with the case where the filter circuit (b) is not provided, the case where the filter circuit (b) is inserted. Is more stable (smaller current fluctuation).

  Returning to FIG. The booster circuit 2 is a separately excited booster circuit that boosts the power supply voltage of a battery or the like to a predetermined voltage. The booster circuit 2 includes an oscillation element and an oscillation transformer (both not shown). When an oscillation control signal is input from an oscillation control means 11 such as a CPU installed outside, the oscillation element is oscillated. Oscillates at a frequency based on the control signal. The oscillation transformer generates electricity with this oscillation (driving) frequency, thereby generating a high voltage. This voltage boosted by the booster circuit 2 is rectified by the rectifier diode 3, and as a result, charges are accumulated in the main capacitor 4 (charging of the main capacitor). After the completion of charging, when a light emission command signal is input to a light emission control circuit (not shown), the charge stored in the main capacitor 4 is caused to flow through a discharge tube (not shown) to discharge the discharge tube.

  Since the booster circuit 2 of the strobe circuit of this embodiment is a separately excited system as described above, the drive frequency oscillated by the booster circuit 2 can be controlled to an arbitrary frequency. In the present embodiment, the drive frequency a is set so that the relationship with the intermediate (IF) frequency b of the transmission / reception signal during communication satisfies the following equation.

a = (b + (b × 2)) / 2 (kHz)
In other words, the drive frequency oscillated by the booster circuit 2 is controlled to be intermediate between the intermediate (IF) frequency of the transmission / reception signal during communication and twice that frequency. In this case, for example, if the IF frequency is 400 kHz, the drive frequency is 600 (= (400+ (400 × 2)) / 2) kHz. When such a frequency is used, fluctuations in the current waveform can be suppressed as shown in FIG. As a result, it is possible to reduce the generation of noise with respect to the IF frequency signal as much as possible, and to prevent troubles in transmission / reception processing.

  In this case, since the driving frequency is high (600 kHz), the inductor 5 of the filter circuit 5 can be downsized, and the filter circuit 5 can be easily incorporated into the strobe circuit.

  As described above, according to the strobe circuit of the present embodiment, since the separately excited booster circuit is employed, the drive frequency can be set to a frequency that does not affect the IF frequency signal as much as possible (noise reduction). The transmission / reception processing during communication is not hindered, communication failure is prevented, and communication quality can be improved. Further, by providing the filter circuit 1, it is possible to further reduce noise.

  In addition, by setting the driving frequency to a high frequency, it is possible to reduce the size of the transmission transformer of the booster circuit 2 as compared with the conventional one, and also to reduce the size of the inductor 5 of the filter circuit 1.

  The strobe circuit according to the present invention is not limited to the above embodiment, and various modifications can be made without departing from the gist of the present invention.

  For example, the strobe circuit of the present embodiment includes the filter circuit 1, but is not limited thereto, and a sufficient noise reduction effect can be expected even when the filter circuit 1 is not provided. In this case, the drive frequency does not need to be set higher than the IF frequency. For example, the drive frequency can be set lower than the IF frequency so as to be intermediate between the IF frequency and a frequency that is ½ the frequency (specifically, Is set so that the driving frequency is 300 (= (400+ (400/2)) / 2) kHz when the IF frequency is 400 kHz.)

  In the strobe circuit according to the present invention, the drive frequency oscillating at the time of charging for strobe photography (light emission) has little influence on the intermediate (IF) signal processing of transmission / reception signals and can be miniaturized. Application to a mobile communication device represented by a mobile phone with a camera function for which quality communication (call) is desired is useful.

1 is a block diagram showing a schematic configuration of a strobe circuit according to an embodiment of the present invention. The figure which shows the power supply drop waveform in A point at the time of charge of the strobe circuit which concerns on the same embodiment (when there is no (A) filter circuit, (B) when a filter circuit is inserted) The figure which shows the relationship between a drive frequency and a current waveform in the strobe circuit which concerns on the same embodiment. (A) is a block diagram showing a schematic configuration of a conventional strobe circuit, (B) is a block diagram showing a configuration of a filter circuit inserted in (A). FIG. 4 is a diagram showing a power supply drop waveform at point A during charging of the strobe circuit according to the conventional example of FIG. 4 ((A) When there is no filter circuit, (B) When a filter circuit is inserted)

Explanation of symbols

1 Filter Circuit 2 Booster Circuit 3 Rectifier Diode 4 Main Capacitor 5 Inductor 6 Capacitor 11 Oscillation Control Means

Claims (3)

In a strobe circuit that controls the light emission of a strobe provided in a mobile communication device with a camera function,
The power supply voltage is boosted to a predetermined voltage by a separately excited booster circuit,
A strobe circuit configured so that the drive frequency oscillated from the booster circuit can be set to a frequency that does not hinder transmission / reception processing during communication.   2. The drive frequency oscillated from the booster circuit is set to a frequency farthest from an integer multiple of an intermediate (IF) frequency of transmission / reception signals during communication or a fraction of an integer. The strobe circuit described in 1. 3. The strobe circuit according to claim 1, wherein a filter circuit is provided between a power supply voltage input unit and the booster circuit.

Images