Detection circuit

This application claims the priority benefit of China application serial no. 201310348811.6, filed on Aug. 12, 2013. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

1. Field of the Invention

The invention relates to a detection circuit, and more particularly, to a detection circuit for detecting a location of a micro-electro-mechanical system.

2. Description of Related Art

A micro-electro-mechanical system (MEMS) is a collection of micro-electro-mechanical components manufactured in a miniaturized structure by using a manufacturing technology much similar to a technology for manufacturing integrated circuits. Nevertheless, in comparison to an integrated circuit in conventional art, a micro-electro-mechanical system apparatus interacts more with environment in terms of interactions such as mechanics, optics or magnetic. The micro-electro-mechanical system apparatus can include tiny electro-mechanical components such as motors, pumps, valves, switches, capacitors, accelerometers, sensors, capacitance sensors, pixel elements, microphones or actuators, etc. Said electro-mechanical components usually accomplish a preset goal by utilizing micro-mechanical structures together with semiconductor components such as the integrated circuit.

The micro-electro-mechanical system is currently an industry with rapid advancement. Moreover, optical elements manufactured by utilizing the micro-electro-mechanical system have gradually become more important in technical fields of telecommunication and computer network. Currently, an optical element with the micro-electro-mechanical system is also applied by a laser based pico projector, such element is known as a MEMS scanning mirror adopting two driving methods including electromagnetic type and electrostatic type. For outputting a projected image, a favorable quality of the projected image can only be obtained when locations of a pixel data and the MEMS scanning mirror are synchronized. Accordingly, it is an essential topic to accurately obtain a location of the micro-electro-mechanical system.

The invention is directed to a detection circuit capable of accurately detecting a location of a MEMS scanning mirror.

A detection circuit of the invention is suitable for detecting a location of a micro-electro-mechanical system. The detection circuit includes an oscillator, a phase lock loop unit, a first low pass filter unit and an amplifying unit. Therein, an input terminal of the oscillator is coupled to the micro-electro-mechanical system, and a first oscillation signal is generated according to an equivalent capacitance value of the micro-electro-mechanical system. The phase lock loop unit performs a phase lock to the first oscillation signal to output a phase lock control signal. The first low pass filter unit is coupled to the phase lock loop unit, and a low pass filtration is performed to the phase lock control signal to generate a filter signal. The amplifying unit is coupled to the first low pass filter unit, and the filter signal is amplified to generate a detection signal.

In an embodiment of the invention, the oscillator includes a blocking capacitor, an inverting unit, a second low pass filter unit, a feedback resistor and a buffer unit.

Therein, an input terminal of the inverting unit is coupled to the micro-electro-mechanical system. The second low pass filter unit is coupled between the input terminal and an output terminal of the inverting unit. The feedback resistor is coupled between the input terminal and the output terminal of the inverting unit. The buffer unit is coupled between the output terminal of the inverting unit and the phase lock loop unit to buffer a voltage outputted by the inverting unit.

In an embodiment of the invention, the detection circuit further includes a blocking capacitor coupled between the micro-electro-mechanical system and the input terminal of the inverting unit.

In an embodiment of the invention, the second low pass filter unit includes a resistor, a capacitor and an inductor. Therein, a terminal of the resistor is coupled to the output terminal of the inverting unit. The capacitor is coupled between another terminal of the resistor and a ground. The inductor is coupled between a common connection point of the resistor and the capacitor, and the input terminal of the inverting unit.

In an embodiment of the invention, the first low pass filter unit includes a resistor and a capacitor. Therein, the resistor is coupled between an output terminal of the phase lock loop unit and an input terminal of the amplifying unit. The capacitor is coupled between the input terminal of the amplifying unit and a ground.

In an embodiment of the invention, the amplifying unit includes an operational amplifier, a first resistor and a second resistor. Therein, a positive input terminal of the operational amplifier is coupled to the first low pass filter unit. The first resistor is coupled between a negative input terminal and an output terminal of the operational amplifier. The second resistor is coupled between the negative input terminal of the operational amplifier and a reference voltage.

In an embodiment of the invention, the amplifying unit further includes a first divider resistor, a second divider resistor and a capacitor. Therein, the second divider resistor and the first divider resistor are connected in series between an operating voltage and a ground, and a common connection point of the first divider resistor and the second divider resistor is configured to generate the reference voltage. The capacitor is coupled between the common connection point of the first divider resistor and the second divider resistor, and the ground.

Based on above, the detection signal corresponding to an equivalent capacitance value of the micro-electro-mechanical system is generated by the oscillator, and the location of the micro-electro-mechanical system can be accurately obtained according to the frequency variation of the detection signal.

To make the above features and advantages of the disclosure more comprehensible, several embodiments accompanied with drawings are described in detail as follows.

FIG. 1 is a block diagram of a detection circuit according to an embodiment of the invention.

FIG. 2 is a schematic circuit diagram of the detection circuit depicted in FIG. 1 .

FIG. 1 is a block diagram of a detection circuit according to an embodiment of the invention. Referring to FIG. 1 , a detection circuit 100 configured to detect a shifted location of a micro-electro-mechanical system includes an oscillator 102 , a phase lock loop unit 104 , a low pass filter unit 106 and an amplifying unit 108 . Therein, an input terminal of the oscillator 102 is coupled to the micro-electro-mechanical system. In FIG. 1 , a capacitor M 1 represents an equivalent capacitance of the micro-electro-mechanical system, and the oscillator 102 generates an oscillation signal SO 1 according to an equivalent capacitance value of the micro-electro-mechanical system. Said oscillation signal SO 1 is a frequency modulation signal. When the micro-electro-mechanical system is driven by a driving signal SD 1 to start operating, a capacitance value of the micro-electro-mechanical system varies with changes of its location. For instance, in case the micro-electro-mechanical system is a motor, a capacitance value of the micro-electro-mechanical system varies with changes of a rotating angle of the motor. On the contrary, in case the capacitance value of the micro-electro-mechanical system is not changed, this indicates that the micro-electro-mechanical system has stopped rotating. Therefore, states of the location of the micro-electro-mechanical system can be obtained according to changes of the capacitance value.

The phase lock loop unit 104 is configured to perform a phase lock to the oscillation signal SO 1 outputted by the oscillator 102 , so as to output the phase lock control signal SO 2 which is phase-locked. The low pass filter unit 106 is configured to perform a low pass filtration to the phase lock control signal SO 2 to reduce a high frequency noise, so as to generating a filter signal SF 1 . The amplifying unit 108 is configured to amplify the filter signal SF 1 in which the high frequency noise has been filtered out, so as to generate a detection signal S 1 . Accordingly, the location of the micro-electro-mechanical system can be accurately obtained according to a voltage variation of the detection signal S 1 .

FIG. 2 is a schematic circuit diagram of the detection circuit depicted in FIG. 1 . More specifically, in an implementation of the detection circuit 100 as shown in FIG. 2 , the oscillator 102 can include a blocking capacitor C 1 , an inverting unit A 1 , a low pass filter unit 202 , a feedback resistor R 1 and a buffer unit B 1 . Therein, the blocking capacitor C 1 is coupled to an input terminal of the inverting unit A 1 ; the low pass filter unit 202 is coupled between the input terminal and an output terminal of the inverting unit A 1 ; the feedback resistor R 1 is coupled between the input terminal and the output terminal of the inverting unit A 1 ; and the buffer unit B 1 is coupled between the output terminal of the inverting unit A 1 and the phase lock loop unit 104 . In the present embodiment, as shown in FIG. 2 , the low pass filter unit 202 includes an inductor L 1 , a resistor R 2 and a capacitor C 2 . Therein, the resistor R 2 and the capacitor C 2 are connected in series between the output terminal of the inverting unit A 1 and a ground, and the inductor L 1 is coupled between the input terminal of the inverting unit A 1 and a common connection point of the resistor R 2 and the capacitor C 2 .

When the micro-electro-mechanical system is driven by a driving signal SD 1 to start operating, the equivalent capacitance M 1 of the micro-electro-mechanical system varies with changes of the location of the micro-electro-mechanical system. Therefore, a capacitor voltage on the equivalent capacitance M 1 of the micro-electro-mechanical system also varies with changes of the location of the micro-electro-mechanical system. A DC component of the capacitor voltage can be filtered out by the blocking capacitor C 1 , and inputted to the output terminal of the inverting unit A 1 and a low pass filter unit 202 . The low pass filter unit 202 is composed of the inductor L 1 , the resistor R 2 and the capacitor C 2 . Therein, the capacitor voltage inputted to the inverting unit A 1 is inverted, and feedbacked by the feedback resistor R 1 to the output terminal of the inverting unit A 1 , so that the inductor L 1 , the resistor R 2 and the capacitor C 2 can start an oscillation. In addition, the low pass filter unit 202 composed of the inductor L 1 , the resistor R 2 and the capacitor C 2 is also capable of filtering out the high frequency noise. The buffer unit B 1 buffers a voltage signal outputted by the inverting unit A 1 so as to output the oscillation signal SO 1 . Since movements of the micro-electro-mechanical system can change the capacitance value of the equivalent capacitance M 1 , an oscillation frequency of the oscillation signal SO 1 is also changed accordingly.

It should be noted that, an implementation of the oscillator 102 is not limited to the present embodiment. For instance, in some embodiments, based on actual applications, at least one of the blocking capacitor C 1 and the buffer unit B 1 can be omitted.

The phase lock loop unit 104 can be implemented by, for example, a 74HC4046 chip, and an implementation thereof is as shown in the FIG. 1 , thus the related description is omitted hereinafter. The phase lock loop unit 104 can perform the phase lock to the oscillation signal SO 1 so as to output the phase lock control signal SO 2 , which means that a frequency variation of the oscillating frequency of the oscillation signal SO 1 can be converted into the voltage variation.

It should be noted that, an implementation of the phase lock loop unit 104 in the present embodiment is merely of an exemplary embodiment, the actual applications are not limited thereto.

In addition, the low pass filter unit 106 can include, for example, a resistor R 3 and a capacitor C 3 , in which the resistor R 3 is coupled between an output terminal of the phase lock loop unit 104 and an input terminal of the amplifying unit 108 , and the capacitor C 3 is coupled between the input terminal of the amplifying unit 108 and a ground. The low pass filter unit 106 composed of the resistor R 3 and the capacitor C 3 can perform the low pass filtration to the phase lock control signal SO 2 so as to filter out the high frequency noise of the phase lock control signal SO 2 such that the filter signal SF 1 can be outputted to the amplifying unit 108 to be processed into signals required by circuits at rear stage.

The amplifying unit 108 can include, for example, an operational amplifier OP 1 , resistors R 4 and R 5 , divider resistors R 6 and R 7 , and a capacitor C 4 . Therein, a positive input terminal of the operational amplifier OP 1 is coupled to the low pass filter unit 106 ; the resistor C 4 is coupled between a negative input terminal and an output terminal of the operational amplifier OP 1 ; the resistor R 5 is coupled between the negative input terminal of operational amplifier OP 1 and a common connection point of the divider resistor R 6 and the divider resistor R 7 ; and the divider resistor R 6 and the divider resistor R 7 are coupled between an operating voltage VCC and a ground. In addition, the capacitor C 4 is coupled between the common connection point of the divider resistor R 6 , the divider resistor R 7 , and the ground.

An amplifying circuit formed of the operational amplifier OP 1 , the resistors R 4 and R 5 can amplify a voltage amplitude of the filter signal SF 1 so as output a detection signal, as shown in FIG. 2 . Accordingly, the location of the micro-electro-mechanical system can be accurately obtained according to the voltage variation of the detection signal S 1 . The capacitor C 4 , the divider resistor R 6 and the divider resistor R 7 can form a regulator circuit which can provide a reference voltage VR to the resistor R 5 , so as to perform a regulation to the amplifying circuit formed of the operational amplifier OP 1 , the resistors R 4 and R 5 .

In summary, according to the invention, the detection signal corresponding to a capacitance value of the micro-electro-mechanical system is generated by the oscillator, and the location of the micro-electro-mechanical system can be accurately obtained according to the voltage variation of the detection signal.