JP2002299960A - Fm detector and fm receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform FM detection of an FM signal of a small modulation index with high sensitivity and high accuracy. SOLUTION: An FM detector is provided with a multiplication circuit 6 for multiplying an input signal, a phase shifting circuit 2 for applying phase shifting by odd number times 90 deg. to a carrier signal outputted from the multiplication circuit 6, a mixer 3 for multiplying an output signal frequency of the phase shifting circuit 2 by an output signal frequency of the multiplication circuit 6, and a lowpass filter 4 to which the output signal of the mixer 3 is inputted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quadrature detector and an FM receiver for performing FM detection in wireless communication.

[0002]

2. Description of the Related Art FIG. 6 shows a configuration of a quadrature detector as an FM detector generally used at present. In this configuration, the FM signal input to the input terminal 1 is branched, and one signal is phase-shifted (phase-shifted) by a phase shift circuit 2 using a gm-C filter or the like, and then input to the mixer 3 and the other signal is input. Is input to the mixer 3 as it is. Therefore, in the mixer 3, a multiplication process is performed between two signals having the same frequency and different phases. The phase shift circuit 2 is set so as to perform a phase shift of an odd multiple of 90 degrees with respect to the center frequency of the input signal, and when the frequency-modulated signal is input to the phase shift circuit 2, the phase shift circuit 2 The amount of phase shift varies accordingly. Since this phase shift amount becomes a low-frequency output of the mixer 3, a baseband output is obtained at the output terminal 5 by passing the output of the mixer 3 through a low-pass filter (LPF) 4.
At this time, the delay time and the amount of phase shift variation by the phase shift circuit 2 are substantially proportional to the amount of phase shift for the carrier signal.

[0003]

In recent wireless systems, modulation schemes having a small modulation index are often used for effective use of frequency. For this reason, the conventional F
In the M detector, when the phase shift amount of the phase shift circuit 2 with respect to the carrier signal is reduced, there is a problem that a sufficient detection output cannot be obtained and the receiving sensitivity is reduced. In addition, when the phase shift amount of the phase shift circuit 2 is increased to secure the sensitivity, there is a problem that the delay time of the phase shift circuit 2 increases and interference occurs between received data.

In a conventional FM receiver, an orthogonal signal output from a complex band-pass filter or RC polyphase filter is input to the above-described FM detector via a circuit for returning the signal to a non-orthogonal differential signal. Therefore, it is difficult to increase the frequency modulation index, and it is difficult to improve the sensitivity.

The present invention has been made in view of the above points, and has as its object to provide an FM detector and an FM detector capable of detecting an FM signal having a small modulation index with high sensitivity and high accuracy. It is to provide a receiver.

[0006]

For this purpose, a first aspect of the present invention provides a multiplying circuit for multiplying an input signal and a phase shifter for performing a 90-degree odd-numbered phase shift on a carrier signal output from the multiplying circuit. An FM detector comprising: a phase circuit; a mixer that multiplies an output signal of the phase shift circuit and an output signal of the multiplier circuit; and a low-pass filter that inputs an output signal of the mixer.

According to a second aspect of the present invention, the input high-frequency signal is
A quadrature mixer circuit for down-converting to two intermediate frequency signals having different degrees of phase, a complex bandpass filter for inputting the two intermediate frequency signals output from the quadrature mixer circuit and performing image signal removal and channel selection. And an FM detector according to the first aspect of the present invention for performing FM detection by inputting an output signal of the complex bandpass filter.

According to a third aspect of the present invention, the input high-frequency signal is
A quadrature mixer circuit for down-converting to two intermediate frequency signals having different phase degrees, an RC polyphase filter for inputting the two intermediate frequency signals output from the quadrature mixer circuit and removing an image signal, 2. The two band-pass filters for performing channel selection by inputting two intermediate frequency signals output from the polyphase filter, and performing FM detection by inputting output signals of the two band-pass filters. An FM receiver comprising the FM detector of the invention.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] FIG. 1 is a block diagram of an FM detector according to a first embodiment of the present invention. In the present embodiment, the input terminal 1 and the phase shift circuit 2 of the circuit shown in FIG.
An N-multiplier circuit 6 is inserted between the mixer and the mixer 3. Therefore, the FM signal input to the input terminal 1 is first multiplied by N in the N multiplying circuit 6. Therefore, the carrier frequency and the modulation index become N times.

The N-multiplier circuit 6 used in the present embodiment can be constituted, for example, by a circuit as shown in FIG. FIG.
601 and 602 are differentially connected pair transistors (NMOSFETs), 603 is a constant current source connected to the sources of the pair transistors 601 and 602,
Is a low-pass filter or a band-pass filter connected to the same source.

In the N multiplying circuit 6, a full-wave rectified signal is obtained by inputting a differential signal to the differential pair transistors 601 and 602. All rectified signals include harmonics of even multiples of the input signal (assuming the input frequency is fo, 2fo, 4f
o, 6fo,...), a doubled signal can be obtained by passing through a low-pass filter, and an arbitrary even-numbered signal of 4 times or more can be obtained by passing through a band-pass filter. .

The input FM signal is converted into N by the N multiplying circuit 6.
After being multiplied and branched, one signal is phase-shifted by the phase shift circuit 2 and then input to the mixer 3, and the other signal is input to the mixer 3 as it is.
A multiplication process is performed between two signals having the same frequency and different phases. The phase shift circuit 2 is set so as to perform a phase shift of an odd multiple of 90 degrees with respect to the center frequency of the input signal. When a frequency-modulated signal is input to the phase shift circuit 2, the phase shift circuit 2 changes the input signal frequency. The amount of phase shift varies accordingly. Since the output of mixer 3 has a component proportional to the amount of phase shift,
The baseband output is obtained at the output terminal 5 by passing the mixer output through the low-pass filter 4.

The amplitude of the baseband output is proportional to the phase shift amount and modulation index of the carrier signal of the phase shift circuit 2, and is inversely proportional to the carrier frequency. Therefore, when the delay time by the phase shift circuit 2 is the same (when the amount of phase shift is proportional to the carrier frequency), the amplitude of the baseband output is proportional to the modulation index and does not depend on the carrier frequency. Therefore, when the delay time uses the same phase shift circuit as that in the related art, the present embodiment increases the baseband output amplitude by N times and improves the sensitivity by N times compared to the related art.

[Second Embodiment] FIG. 3 shows a second embodiment of the present invention.
It is a block diagram of the FM receiver of an embodiment. In FIG. 3, 6A is a doubler circuit, 7 is an RF (FM high frequency) signal input terminal, 8 and 9 are mixers, 10 is a local signal input terminal, and 11 is a π / which phase-shifts the local signal by π / 2. 2 is a phase shifter, and 12 is a complex bandpass filter, and the other components are the same as those in FIG.

In this embodiment, the RF signals are transmitted to the mixers 8 and 9.
After down-conversion by a quadrature mixer circuit composed of a .pi. / 2 phase shifter 11, channel selection and image signal removal are performed by a complex band-pass filter 12. Thereafter, demodulation is performed by the FM detector described in the first embodiment. In the present embodiment, an FM detector using a doubler circuit 6A as the N multiplier circuit 6 is shown.

Since the output of the complex band-pass filter 12 is a quadrature differential signal, the doubling circuit 6A is formed by a general circuit using transistors as shown in FIG. In FIG. 4, reference numerals 611 and 612 denote pair transistors (NMOSFETs), 613 denotes a load resistor, and 614 and 61.
5 is a pair transistor (NMOSFET), 616 is a load resistor, and 617 is a constant current source. Here, I and Q represent the quadrature input signals output from the mixers 8 and 9, and -I and -Q
Represents each inverted input signal. In the present embodiment, the baseband output amplitude is doubled as compared with the related art,
The sensitivity is doubled.

[Third Embodiment] FIG. 5 shows a third embodiment of the present invention.
It is a block diagram of the FM receiver of an embodiment. 5, 13 is an RC polyphase filter, 14 and 15 are bandpass filters, and the other components are the same as those in FIG.

In this embodiment, the RF signals are transmitted to the mixers 8 and 9.
After down-conversion by a quadrature mixer circuit composed of a .pi. / 2 phase shifter 11, the image signal is removed by an RC polyphase filter 13, and channel selection is performed by band-pass filters 14 and 15. Thereafter, demodulation is performed by the FM detector described in the first embodiment. The present embodiment also shows a case of an FM detector using a doubler circuit 6A as the N multiplier circuit 6. Also in this embodiment, the baseband output amplitude is doubled and the sensitivity is doubled as compared with the related art.

[Other Embodiments] In the second and third embodiments described above, the N multiplying circuit 6 is a 2
Although the multiplying circuit 6A is used, it goes without saying that various multiplying circuits such as a quadruple multiplying circuit, a six-multiplying circuit, or an eight-multiplier multiplying circuit for increasing the modulation index may be used.

[0020]

As described above, according to the FM detector of the present invention,
After multiplying the received FM signal by N to increase the modulation index, F
Since M detection is performed, an FM receiver that detects an FM signal having a small modulation index with high sensitivity and high accuracy can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram of an FM detector according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of an N-multiplier used in the FM detector of FIG. 1;

FIG. 3 is a block diagram of an FM receiver according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram of a doubler used in the FM receiver of FIG. 3;

FIG. 5 is a block diagram of an FM receiver according to a third embodiment of the present invention.

FIG. 6 is a block diagram of a conventional FM detector.

[Explanation of symbols]

1: input terminal, 2: phase shift circuit, 3: mixer, 4: low-pass filter, 5: output terminal, 6: N multiplier, 6A: 2
Multiplier circuit, 601, 602: pair transistor, 60
3: constant current source, 611, 612: pair transistor, 6
13: load resistance, 614, 615: pair transistor,
616: load resistance, 617: constant current source, 7: input terminal,
8, 9: mixer, 10: input terminal, 11: π / 2 phase shifter, 12: complex bandpass filter, 13: RC polyphase filter, 14, 15: bandpass filter.

Continuation of the front page F term (reference) 5K020 CC03 DD05 EE05 FF13 FF15 HH11 HH13 MM02

Claims (3)

[Claims] 1. A multiplication circuit for multiplying an input signal, a phase shift circuit for performing a phase shift of an odd multiple of 90 degrees with respect to a carrier signal output from the multiplication circuit, an output signal of the phase shift circuit, and the multiplication An FM detector comprising: a mixer that multiplies an output signal of a circuit; and a low-pass filter that inputs an output signal of the mixer. 2. A quadrature mixer circuit for down-converting an input high-frequency signal into two intermediate frequency signals having a phase difference of 90 degrees, and an image signal removal by inputting the two intermediate frequency signals output from the quadrature mixer circuit. 2. A complex band-pass filter for performing channel detection and channel selection, and performing FM detection by inputting an output signal of the complex band-pass filter.
An FM receiver, comprising: an M detector. 3. A quadrature mixer circuit for down-converting an input high-frequency signal into two intermediate frequency signals having a phase difference of 90 degrees, and inputting the two intermediate frequency signals output from the quadrature mixer circuit to remove an image signal. And a channel selection by inputting two intermediate frequency signals output from the RC polyphase filter.
2. The FM detection apparatus according to claim 1, wherein the FM detection is performed by inputting the output signals of the two band-pass filters and the two band-pass filters.
An FM receiver, comprising: a detector.