JPH0810980Y2 - FSK receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to an FSK receiver, and more particularly to an FSK receiver that employs a quadrature detection reception method using a gyrator filter.

[Conventional technology]

Recent advances in integrated circuit technology have made receivers smaller. However, taking the wireless unit as an example, the basic circuit scheme is the same, so that it is impossible to integrate it, or the existence of difficult elements is approaching the limit of miniaturization. For example, in a superheterodyne receiver, high frequency and intermediate frequency filters require a large area. Therefore, a quadrature detection reception system has been considered to reduce the size and weight.

In the quadrature detection reception method, the line frequency and the local oscillation frequency are made equal, and the beat of the reception frequency and the local oscillation frequency is taken out by the mixer, and only the baseband signal is made by the low-pass filter, and the amplitude of this beat is limited by the limiter circuit. In this method, demodulation processing is performed to obtain a demodulated signal.
The quadrature detection reception method is characterized in that there is no image frequency because the intermediate frequency becomes zero because the local oscillation frequency and the line frequency match. This means that a high selectivity filter for attenuating the image frequency is not required at all in the high frequency amplifier and the intermediate frequency amplifier. Also, since the channel filter for attenuating the adjacent channel interference wave has an intermediate frequency of zero, it can be configured with a low frequency active filter. For example, an external CR as shown in the circuit diagram of FIG. 4 can be used. There was an active filter consisting of components and a voltage follower 32.

[Problems to be solved by the device]

The conventional FSK receiver described above can eliminate the high-frequency filter, the intermediate-frequency filter, and the like by using the quadrature detection reception method, so that the receiver can be made compact and lightweight. However, since the input signal of the filter is a baseband signal, the frequency is as low as several kilohertz, and when a ladder-type active filter is configured, the resistance value is calculated from the relationship of the time constant as shown in the circuit diagram of FIG. When set to 100 kΩ, the capacitance of the capacitor is several thousand pF
To tens of thousands of pF. For this reason, it becomes impossible to realize the above-mentioned capacitor on the integrated circuit, and many elements are required outside the integrated circuit, which causes a serious obstacle to downsizing and weight saving of the receiver. Further, if the circuit is constructed by a passive filter in order to reduce the number of external circuit elements, the value of the coil becomes large due to the low frequency, which causes a drawback that the receiver can be made smaller and lighter.

[Means for Solving the Problem] An FSK receiver of the present invention is an oscillator that oscillates at the same frequency as the frequency of the FSK reception signal frequency-shift keyed with a binary digital signal and an output signal of the oscillator is branched into two. The in-phase signal and the 90 ° phase-shifted signal are respectively supplied as local oscillation signals, mixed with the FSK reception signal, and mixed with each other.
First and second mixer circuits for generating 0-degree phase-shifted baseband signals, and first and second low-pass filters for limiting the output signals of the first and second mixer circuits by noise bands, respectively. In an FSK receiver having a quadrature detection demodulation circuit that obtains a demodulation signal from the output signals of the first and second low pass filters, each of the first and second low pass filters receives an input voltage V ₁ as a voltage. The first transconductance amplifier that converts current (hereinafter referred to as TCA
And a second TCA for inputting the output signal of the first TCA, converting the polarity to a voltage having a polarity opposite to that of the input voltage V ₁ and feeding back to the input of the first TCA, and the first TCA. A first capacitor connected to the output of the first TCA to generate a voltage V _c between the other end and an equivalent ground point, and a first capacitor connected to the output of the first TCA to convert the voltage V _c into a current. A third TCA and a fourth TCA which is connected to the output of the third TCA and converts the polarity to a voltage having a reverse polarity to the voltage V _c and returns to the input of the third TCA.
And a second capacitor connected to the output of the third TCA to generate a voltage V ₂ between the other end and an equivalent grounding point, and the first to fourth TCAs and the first capacitor. The first and second low-pass filters are formed by the equivalent inductance formed by the capacitor and the second capacitor.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention. The received wave that has been frequency-modulated with the binary digital signal of the mark or space is amplified by the high frequency amplifier 101, divided into two, and input to the mixer circuits 102A and 102B, respectively. Further, the local oscillation frequency is input to the 90-degree phase shifter 108 from the voltage-controlled oscillation circuit 109 and the phase is rotated by +45 degrees and -45 degrees, respectively, and the mixer circuit 102
Input to A and B. The mixer circuits 102A and 102B output baseband signals that are 90 degrees out of phase with each other. As described above, since the line frequency and the local oscillation frequency match, the baseband signal becomes the beat frequency. The low-pass filter 103 extracts only the baseband signal,
It limits the band of noise and is composed of a gyrator filter described later. The baseband signals are input to the limiter circuit 104 and binarized.
I and Q are obtained, and frequency detection is performed by the demodulation circuit 105 (for example, a D-type flip crop circuit). As shown in the waveform diagram of FIG. 2, assuming that the waveform of the modulated data is data M, this frequency detection signal changes the phase of the modulation signals I and Q by 90 degrees, so that the output L also changes. The original data M is demodulated. The demodulated signal demodulated in this way passes through a low-pass filter 106 for removing noise and is binarized by a comparator 107 and output as a binary digital signal.

Next, a gyrator filter used in the low pass filter 103 will be described with reference to the circuit diagrams and block diagrams of FIGS. 3 (a) and 3 (b). This gyrator
The filter basically has a function equivalent to that of a low pass filter composed of an inductance L ₁ and a capacitance C ₁ shown in FIG. 3 (a). In FIG. 3B, the transconductance amplifier 33 is a voltage-current conversion circuit, and if the input potential difference is V ₁ and the output current is I _o , the transconductance G is expressed as follows.

G = dI _o / dV ₁ If each current and each voltage are set as shown in FIG. 3 (b), I ₀₁ = GV ₁ (1-1) I ₀₂ = GV ₂ (1-2) ) I ₁ = GV _c (1-3). Further, since V _c = I _c / jωC ₂ ω: input angular frequency ... (2-1) I ₀₂ = I ₀₁ + I _c ... (2-2), the equation (2-1 to 2) is used. By substituting the equations (1-1 to 3) and erasing and arranging V _c , it becomes (V ₁ −V ₂ ) / I ₁ = jωC ₂ / G · G. This is L ₁ = C ₂ /
Considering G · G, (V1-V2) / I ₁ = jωL ₁ This is equivalent to the floating L _{1 in} FIG. 3 (a), and can be expressed by L ₁ = C ₂ / G · G. That is, if the transconductance G decreases, the L value increases with the same capacitance. In FIG. 3 (b), 32 is a voltage follower, which is used before and after the gyrator filter for impedance conversion. Floating L1 is realized by using four transconductance amplifiers 33 and C2. Reference numeral 31 is a bias circuit for the transconductance amplifier 33.

The low pass filter 103 using the above configuration is an IC
It can be realized on a chip.

[Effect of device]

As described above, the present invention uses a gyrator filter that uses a transconductance amplifier as a low-pass filter, so that an equivalently large coil can be obtained.
C which is an external component that can be realized on the IC chip and was necessary because it was composed of an RC active filter in the past.
The R can be installed in the IC chip, which is extremely effective in reducing the size and weight of the radio section of the FSK receiver.

[Brief description of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, FIG. 2 is a waveform diagram for explaining this embodiment, and FIGS. 3 (a) and 3 (b) are circuits of a gyrator filter which is a main part of FIG. FIG. 4, a block diagram, and FIG. 4 are circuit diagrams of a conventional low-pass filter. 101 …… High frequency amplifier, 102A, B …… Mixer circuit, 103 ……
Low pass filter, 104 ... Limiter circuit, 105 ... Demodulation circuit, 106 ... Low pass filter, 107 ... Converter circuit, 108 ... 90 degree phase shifter, 109 ... Local oscillation circuit.

Claims (1)

[Scope of utility model registration request] 1. An oscillator which oscillates at the same frequency as the frequency of an FSK reception signal frequency-shift keyed by a binary digital signal and a signal obtained by bifurcating the output signal of the oscillator and shifting the phase by 90 degrees from the in-phase signal. Are supplied as local oscillation signals and are mixed with the FSK reception signal to generate baseband signals that are phase-shifted by 90 degrees from each other. Outputs of the first and second mixer circuits and the outputs of the first and second mixer circuits. FS having first and second low-pass filters for limiting the noise band of each signal and a quadrature detection demodulation circuit for obtaining a demodulated signal from the output signals of the first and second low-pass filters
In the K receiver, each of the first and second low pass filters converts a first transconductance amplifier into a voltage-current conversion input voltage V ₁ (hereinafter referred to as transconductance amplifier TC
A), a second TCA for inputting the output signal of the first TCA, converting the polarity to a voltage having a polarity opposite to that of the input voltage V _1, and returning the voltage to the input of the first TCA; A first capacitor connected to the output of the TCA to generate a voltage V _c between the other end and an equivalent ground point; and a voltage connected to the output of the first TCA to convert the voltage V _c into a current. A third TCA, a fourth TCA connected to the output of the third TCA, which converts the polarity of the voltage V _c to a voltage having a reverse polarity and returns to the input of the third TCA, A second capacitor connected to the output of the TCA and generating a voltage V ₂ between the other end and an equivalent ground point, and is formed by the first to fourth TCA and the first capacitor. FSK, characterized in that the first and second low-pass filters are formed by an equivalent inductance and the second capacitor. Shin machine.