Patent Application
20170243044
The present disclosure relates to a signal conversion circuit and a fingerprint identification system, and in particular, relates to a signal conversion circuit and a fingerprint identification system having a simple circuit structure.
With the development of science and technology, more and more portable electronic devices, such as mobile phones, digital cameras, tablet computers, laptop computers and the like, have become indispensable in people's life. Since the portable electronic devices are generally used by individuals and store some private data, the data stored in the electronic device, such as address books, pictures, personal information and the like, is privately owned. If an electronic device is lost, the data therein may be used by others, which may cause unnecessary losses. An electronic device may be prevented from being used by others by means of password protection. However, a password is easily leaked or cracked. Therefore, data security is low. In addition, users may use an electronic device only when inputting a correct password. If the password is forgotten, much inconvenience may be caused to the users. Therefore, a personal fingerprint identification system has been currently developed for identity authentication to improve data security.
Generally, a fingerprint identification system uses a pixel array circuit to receive a contact of a finger, and the pixel array circuit converts a capacitance formed between the pixel array circuit and the finger into a pixel output signal. Since the pixel output signal is an analog signal, the pixel output signal needs to be firstly converted into a digital signal, and then the digital signal is sent to a fingerprint judging module to determine whether the pixel array circuit corresponds to a finger ridge or a finger valley of the fingerprint. In the customary technologies, the pixel output signal is converted by an analog-to-digital converter (ADC) from an analog pixel output signal into a digital pixel output signal. However, the analog-to-digital converter has a complicated circuit structure, and thus need to occupy a large circuit area; furthermore, the production cost is increased and high power is consumed. Therefore, a conversion circuit with a simple circuit structure, a small circuit area, low cost and low power consumption is desired in the industry.
Therefore, a main objective of the present disclosure is to provide a signal conversion circuit and a fingerprint identification system with simple circuit structure, small circuit area, low cost and low power consumption.
To solve the above technical problem, the present disclosure provides a signal conversion circuit. The signal conversion circuit is configured to generate a first digital signal according to a first analog signal, and includes a comparator and counter. The comparator includes a first input terminal configured to receive the first analog signal, a second input terminal connected to a reference voltage generator and configured to receive a reference voltage, and an output terminal, configured to output a second digital signal. The counter is connected to the output terminal, and is configured to generate a first digital signal.
Preferably, when the first analog signal is greater than the reference voltage, the second digital signal has a first potential, and when the first analog signal is less than the reference voltage, the second digital signal has a second potential.
Preferably, the signal conversion circuit is used in a fingerprint identification system. The fingerprint identification system includes a pixel array circuit, and the first input terminal is connected to the pixel array circuit.
Preferably, the pixel array circuit is configured to receive a contact of a finger, and convert a capacitance formed between the pixel array circuit and the finger into a pixel output signal. The pixel output signal is correlated to the first analog signal.
Preferably, the fingerprint identification system includes an amplifier, and the amplifier is connected between the pixel array circuit and the first input terminal, and configured to enhance a signal strength of the pixel output signal to form the first analog signal.
Preferably, a signal-to-noise ratio of the first analog signal is less than 3.
Preferably, the reference voltage generator includes a control circuit. The control circuit generates a definite voltage.
Preferably, the reference voltage generator further includes a digital-to-analog converter. The digital-to-analog converter is connected to the control circuit, and is configured to convert the definite voltage into the reference voltage.
To better solve the above technical problem, the present disclosure further provides a fingerprint identification system, the fingerprint identification system includes:
a pixel array circuit, configured to receive a contact of a finger, and convert a capacitance formed between the pixel array circuit and the finger into a pixel output signal;
a signal conversion circuit, connected to the pixel array circuit, and configured to generate a first digital signal according to a first analog signal, where the signal conversion circuit includes:
a comparator, including:
a counter connected to the output terminal, and configured to generate a first digital signal; and
a fingerprint judging module, connected to the signal conversion circuit, and configured to judge, according to the first digital signal, whether the pixel output signal corresponds to a finger ridge or a finger valley.
A signal conversion circuit according to the present disclosure retrieves a desired signal in a first analog signal and converts the desired signal into a first digital signal in the case of a low signal-to-noise ratio by using a comparator and a counter. The signal conversion circuit according to the present disclosure may replace a conventional ADC, and has the advantages of simple circuit structure, small circuit area, low cost and low power consumption.
In order to make the objectives, technical solutions, and advantages of the present disclosure clearer, the present disclosure is further described in detail below by reference to the embodiments and the accompanying drawings. It should be understood that the embodiments described here are only exemplary ones for illustrating the present disclosure, and are not intended to limit the present disclosure.
Referring to
The working principle of the signal conversion circuit 10 is described as follows. The first analog signal VA include a desired signal sig and noise noi; that is, the first analog signal VA is an accumulated result of the desired signal sig and noise noi, and the mathematical formula may be expressed as: VA=sig+noi, in which the noise noi complies with a probability distribution. It should be noted that the probability that the first analog signal VA is greater than the reference voltage VR (referred to as Pr(VA>VR)) and the desired signal sig have monotonicity, that is, the greater the desired signal sig, the greater the probability (Pr(VA>VR)) that the first analog signal VA is greater than the reference voltage VR; on the contrary, the smaller the desired signal sig, the smaller the probability (Pr(VA>VR)) that the first analog signal VA is greater than the reference voltage VR. In other words, the probability (Pr(VA>VR)) that the first analog signal VA is greater than the reference voltage VR reflects the strength of the desired signal sig. In the other respect, through sampling for N times (N is a positive integer), the first digital signal VD1 (which is the accumulated result of the second digital signal VD2) may reflect the probability (Pr(VA>VR)=VD1/N) that the first analog signal VA is greater than the reference voltage VR, that is, the first digital signal VD1 may reflect that the strength of the desired signal sig. Simply, the signal conversion circuit 10 may retrieve the strength of the desired signal sig in the first analog signal VA by using the comparator 100 and counter 102, and become the first digital signal VD1.
In the other aspect, the signal conversion circuit 10 is applicable to a system with a low signal-to-noise ratio (SNR), and particularly to the system with the SNR less than 3 (lower than 4.77 dB), for example, a fingerprint identification system. Referring to
As seen from the above embodiment, a signal conversion circuit according to the present disclosure retrieves a desired signal in a first analog signal and converts the desired signal into a first digital signal in the case of a low signal-to-noise ratio by using a comparator and counter. The signal conversion circuit according to the present disclosure may replace a conventional ADC, and has the advantages of simple circuit structure, small circuit area, low cost and low power consumption.
It should be noted that the preceding embodiments are used to describe the concepts of the present disclosure. A person skilled in the art may make different modifications to the present disclosure without any limitation to the above given embodiments. For example, the amplifier is only used to enhance the signal strength of the pixel output signal Vo, which is not limited thereto. In case that the signal strength of the pixel output signal is sufficient, the fingerprint identification system may directly connect the positive input terminal of the comparator to the pixel array circuit, which also pertains to the scope of the present disclosure. In addition, the reference voltage generator may directly generate an analog reference voltage, without the need of using a digital-to-analog converter to convert the analog reference voltage.
To sum up, in the present disclosure, a desired signal in a first analog signal is retrieved and the desired signal is converted into a first digital signal in the case of a low signal-to-noise ratio only by using a comparator and counter. The signal conversion circuit of the present disclosure may replace an ADC applicable to a fingerprint identification system, such that the fingerprint identification system has the advantages of simple circuit structure, small circuit area, low cost and low power consumption.
The above descriptions are merely preferred embodiments of the present disclosure, but not intended to limit the present disclosure. Any modification, equivalent replacement, and improvement made without departing from the spirit and principle of the present disclosure shall fall within the protection scope of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201510685724.9 | Oct 2015 | CN | national |
The present application is a continuation of international application No. PCT/CN2016/071680, filed on Jan. 21, 2016, which claims priority to Chinese Patent Application No. CN201510685724.9, filed on Oct. 21, 2015, both of which are hereby incorporated by reference in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/CN2016/071680 | Jan 2016 | US |
| Child | 15590060 | US |
