JPH0666152U - FSK demodulation circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] It is an object of the present invention to provide a circuit that enables adjustment of the demodulation circuit of the FSK receiving circuit and reduction of the number of parts of the circuit configuration, simplification in production, and power saving. . [Structure] High-frequency amplification is performed using a C-MOS-INVIC, and demodulation waveform amplification, waveform shaping, and reference voltage generation are all performed by a single-chip IC. Note that the FSK demodulation uses a ceramic discriminator to perform no adjustment, and an impedance matching buffer amplifier is provided.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an FSK demodulation circuit in FSK modulation communication used for data communication and the like.

[0002]

[Prior art]

 The data communication is performed by a method of performing FSK (Frequency Shift Keying) modulation on data of 1 and 0 and performing communication. In the case of ordinary wireless communication, the receiver uses high-frequency amplification, conversion to an intermediate frequency, and amplification and demodulation with a demodulation circuit.In short-distance communication, the receiver only uses high-frequency amplification and the intermediate frequency Some demodulation is performed directly by a demodulation circuit without passing through conversion or BPF (bandpass filter), but with respect to FSK demodulation, both are demodulated by the same method.

As one method of the FSK demodulation method, there is a quadrature detection circuit shown in FIG. The operation of FIG. 3 will be briefly described. An appropriate frequency is given to the 1 and 0 signals, and the carrier wave is FS modulated by the given frequency and transmitted. When the transmitted radio wave is received, it is input to the demodulation IC from the IF IN terminal. The demodulation IC is provided with a modulation circuit for tuning the frequency directly or at the intermediate frequency of the frequency modulated by the frequency of the signal 1. Therefore, only the tuned frequency becomes high level, and the other frequencies are output as low level from the output terminal. By amplifying and demodulating this signal, the 1,0 signal is extracted. For this reason, it was necessary to adjust this tuning circuit and take measures for temperature compensation.

[0004]

[Problems to be solved by the device]

 However, in the conventional technology as described above, a specific IC such as an IF IC must be used, and a low gain frequency amplifier, an FSK demodulator, and a single function only for waveform shaping, and low cost. It was difficult to reduce the number of parts and lower the current when using it for required circuits.

Further, in an IC including a waveform shaping circuit for a pager or the like, the rise time of the reference voltage of the internal comparator has a delay, which causes a delay in the output of the FS demodulation signal. The present invention has been made for the purpose of ameliorating such drawbacks of the conventionally known FSK demodulation circuit.

[0006]

[Means for Solving the Problems]

 A high-frequency circuit that amplifies the input signal, a matching circuit that matches its output with the demodulation circuit, and the demodulation circuit with a ceramic discriminator that sets the reference voltage with the output of the reference voltage circuit that maintains the reference voltage at a constant value. Of the circuits in which a low-frequency amplifier circuit for amplifying the demodulated signal and a waveform shaping circuit for shaping the output waveform thereof are connected in series, the matching circuit described above and a circuit other than the demodulation circuit are configured by one IC.

[0007]

[Action]

 The reference voltage value in the FSK demodulation circuit is equivalent to the ground potential of the FSK demodulation circuit raised by providing a reference voltage circuit and supplying its output to a constant voltage. The FSK demodulated signal is obtained.

[0008]

【Example】

FIG. 1 is a circuit diagram showing an embodiment of the present invention. It will be described with reference to the drawings. In the figure, 1 is a high frequency amplifier circuit, and Q ₁ and Q ₂ are inverters. Reference numeral 2 is a buffer amplifier of a transistor circuit that outputs from the emitter, and also serves as a matching circuit that also performs impedance matching with the next-stage demodulation circuit. Reference numeral 3 is a demodulation circuit using a ceramic discriminator (CD). The demodulation circuit 3 is installed at a high frequency with a capacitor C ₄ . Reference numeral 4 is a reference voltage circuit for generating the reference potential of the demodulation circuit 3. Reference numeral 5 is a low-frequency amplifier circuit for amplifying the demodulated signal, and 6 is a waveform shaping circuit for shaping the signal waveform.

The operation of the above circuit will be described. The received signal input from the antenna is amplified by the high frequency amplifier circuit 1. This high frequency amplifier circuit is an amplifier which includes inverters Q ₁ and Q ₂ and does not have a BPF circuit. The received signal amplified here is amplified by the transistor Q ₃ of the buffer amplifier 2 and output by the emitter follower. This emitter follower output is intended for impedance matching with the demodulation circuit 3 in the next stage.

The demodulation circuit 3 shows, for example, a detection characteristic diagram of a ceramic discriminator with a trade name of SFD455S4 in FIG. That is, if the frequency is low centering on the frequency of 455 KHz, the (+) DC output voltage is obtained, and if the frequency is high, the (-) DC output voltage is obtained. On the contrary, some ceramic discriminators have a (−) DC output voltage at a frequency higher than the center frequency and a (+) DC output voltage at a lower frequency than the center frequency. The center frequency may be different depending on the special order.

Therefore, it can be understood that the high frequency FSK transmission frequency in the case of this embodiment is a frequency shifted to both sides by a frequency corresponding to 1 and 0 centered at 455 KHz.

In the demodulation circuit 3, the reference voltage circuit 4 generates a voltage half the power supply voltage. This can be easily output by using an inverter IC. By supplying the output voltage of the reference voltage circuit 4 to the ceramic discriminator (CD) as a reference potential, it is separated from the ground potential of the ceramic discriminator (CD) to maintain the 1/2 reference point of FSK demodulation. A stable demodulated signal can be obtained by eliminating the rising delay of the signals of 1, 1, 0. The output of the demodulation circuit 3 is amplified to a required level by the low frequency amplification circuit 4, and the output signal is shaped by the waveform shaping circuit 6 to obtain the FSK signal.

By using the ceramic discriminator (CD) in the demodulation circuit as described above, it is not necessary to provide a tuning circuit in the demodulation circuit 3 to perform tuning adjustment. Further, all the circuits including the receiving circuit need only one C / MOS inverter IC except for the transistor of the buffer amplification / matching circuit (3) and the ceramic discriminator (CD) of the demodulation circuit 4, so that the circuit is downsized. The manufacturing cost can be reduced and the power consumption can be saved. In the embodiment, the reception frequency is close to 455 KHz, but in the case of data communication by a normal radio, the SHF. UHF. It goes without saying that the demodulation circuit of the present invention can be used by converting the intermediate frequency up to around 455 KHz regardless of the VHF band.

[0014]

[Effect of device]

 By using a ceramic discriminator in the demodulation circuit according to the present invention and supplying the reference potential thereof by the reference voltage circuit, the delay of the rising characteristic of the FSK signal is eliminated and the waveform collapse is suppressed, and the matching circuit of the buffer amplifier. Other active elements can be configured with a 1-chip C / MOS inverter IC, so the number of parts can be greatly reduced compared to the conventional circuit, and it is possible to reduce size, simplify manufacturing, and save power. The above effect is great.

[Brief description of drawings]

FIG. 1 is an FSK demodulation circuit diagram showing an embodiment of the present invention.

[Figure 2] Characteristic diagram of ceramic discriminator

FIG. 3 is a schematic diagram of a conventional demodulation circuit.

[Explanation of symbols]

 1 high frequency amplifier circuit 2 buffer amplifier 3 demodulation circuit 4 reference voltage circuit 5 low frequency amplifier circuit 6 waveform shaping circuit

Claims (2)

[Scope of utility model registration request] 1. A high frequency amplifier circuit 1 for receiving and demodulating circuit, a buffer amplifier 2 for impedance matching with a next stage demodulating circuit, a demodulator circuit 3 of a ceramic discriminator, a low frequency amplifier circuit 5, and a waveform shaping circuit 6. A cascade connection is adopted, and a reference voltage circuit 4 is provided for the reference potential of the ceramic discriminator and its output voltage is supplied to raise the ground potential equivalently.
SK demodulation circuit. 2. An FSK demodulation circuit in which the high-frequency amplification circuit 1, the low-frequency amplification circuit 4, the waveform shaping circuit 6, and the reference voltage circuit 4 are formed by a one-chip C-MOS-IC.