JPS59219005A - Quadrature detector - Google Patents

Abstract

PURPOSE:To improve the detection output characteristic and the distortion characteristic by controlling the gain of a multiplier by a signal obtained by detecting an AM component produced with the amplitude characteristic of a single tuning circuit provided with a phase shifter. CONSTITUTION:An FM intermediate frequency signal obtained at an output of the phase shifter 1 having the single tuning circuit and the original intermediate frequency signal are applied to the multiplier 3. Further, the AM component produced by the amplitude characteristic of the single tuning circuit is detected by a detector 5. Then, an output of the detector 5 is given to a control input of a variable current source 7 via an inverting circuit 6 to control the gain of the multiplier 3.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a Fordracher detector as an FM detector in an FM receiver.

The Ford Lacher detector uses a multiplier to multiply the FM intermediate frequency (IF) signal by a signal that has passed through a phase shifter whose output phase changes with respect to the input phase when the frequency changes, and then converts the intermediate frequency (10.7MHz) or higher frequency components are attenuated to obtain an audio signal, that is, an FM detection output, but the multiplier can generally be configured with a double-balanced differential amplifier circuit, and the external circuit is Since only a phase shifter is required, it is suitable for IC implementation.

Conventionally, there has been a detector of this type as shown in FIG. In the figure, 1 is a phase shifter, which consists of inductance coils Ll and L2, a resistor R1, and a capacitor C+, and R+, C+, and L2 constitute a simple single-tuned circuit. 2 is a differential amplifier connected to the input side of phase shifter 1 to drive it, and transistor Q+ −
Q3, resistors R2 and R3, and capacitor C2, and the FM center frequency signal is input to the input terminal Tin. The phase shifter 1, including the differential amplifier 2, is represented by an equivalent circuit as shown in FIG. 2, and as shown in FIG.
At the intermediate frequency of the signal to the input [0, to the signal at the output 9
It produces a phase shift of 0°, and works to change the amount of phase shift as it deviates from fo.

3 is a multiplier, which is constituted by a double-balanced differential amplifier circuit consisting of transistors Q4 to Q+o, resistors R4 to R7, constant voltage source VB+, and Va2.
The FMIF signal is converted into an audio signal by multiplying the output signal of the phase shifter 1 applied to the base of the transistor Q4 by the IF multiplied signal applied to the base of the transistor Q8. Note that 4 is an amplifier that amplifies the output signal of the multiplier 3 and outputs it to the output terminal TQIIT, and is composed of an operational amplifier A and resistors R8 and R9.

As shown in Fig. 1, in a conventional Ford Lacher detector using an inductance coil L1 and a single tuned circuit (R1+C+, L2) as the phase shifter 1, the linear range of the detected output is limited as shown in Fig. 4. It had the disadvantage of having a narrow width and poor distortion characteristics. To overcome this drawback, the phase shifter can be double tuned, but if you do this, tJ! i
Another problem arises in that the adjustment becomes complicated.

The present invention has been made to solve the above-mentioned conventional problems, and detects the AM component generated by the amplitude characteristics of the single-tuned circuit included in the phase shifter, and uses the signal obtained by the detection to adjust the gain of the multiplier. The object of the present invention is to provide a Fordratch detector with improved detection output characteristics and distortion characteristics through control.

The present invention will be described below with reference to FIG. 5 and subsequent figures, in which parts equivalent to those of the conventional example are given the same reference numerals.

FIG. 5 is a block diagram showing the principle of the Ford Lacher detector according to the present invention. In the figure, the FMIF signal is input to a phase shifter 1 and a multiplier 3. The output of phase shifter 1 is multiplier 3
is connected to one input of the AM detector 5 as well as to the AM detector 5. The output of the AM detector 5 is connected to a control input of a variable current source 7 via an inverting circuit 6. When a double-balanced differential amplifier circuit is used as the multiplier 3, block 7 can be incorporated into the multiplier 3 by making the constant current source of the differential amplifier circuit a variable type. .

Since the single-tuned circuit used in the phase shifter 1 has an amplitude characteristic, when its output is subjected to AM detection in the ΔM detector 5, a detection characteristic as shown in FIG. 6 is obtained. Looking at this characteristic, the AM detection output decreases when detuned to the + side and the - side.

Therefore, if this A-M detection output is inverted in the inverting circuit 6 and then used to control the gain of the multiplier 3, the decreasing detection output is corrected and the FM
The linear range of the detection output characteristics is expanded, and the distortion characteristics are greatly improved (in Fig. 7, the dotted line shows the conventional characteristics, and the solid line shows the characteristics of the present invention). A specific example of a circuit of a Ford Lacher detector constructed based on the principle shown in the following is shown below.

The illustrated circuit includes a voltage-current conversion circuit consisting of a transistor Q11 and a resistor Rho, a transistor 12 and a resistor Ru, and a transistor (h
3. Q and transistor Q+6. A switching circuit consisting of QE, a limiter circuit consisting of transistors Q+v to Q19, resistors R12 to R, and S, and a current mirror circuit consisting of diode D1 and transistor Q2° are added. The signal that has passed through the phase shifter 1 is converted into a current signal by a transistor Q11, and then switched by a switching circuit consisting of transistors Q13 and Ql4 and transistors QCs and Ql6, respectively. The switched signal is applied to a limiter circuit including transistors QIT and Ql, and its AM component is synchronously detected by the switching. The AM detection output is applied to the collector of the current source transistor Qlo of the double-balanced differential amplifier circuit via the transistor Q2o of the current mirror circuit to control the current source. By controlling this current source, the gain of the multiplier is increased in response to a decrease in the AM detection output. Therefore, the distortion characteristics can be improved by linearizing the detection output characteristics for input signals that deviate from the center frequency rO to the + side. Note that an FM detection output signal is obtained at the output of the amplifier 3.

Although the circuit shown in FIG. 8 uses a synchronous detection type AM detection circuit, other detection methods such as diode detection may be used instead.

Furthermore, the circuit that controls the current source using the AM detection output can also have any configuration other than that shown in FIG.
Any device may be used as long as it can control the current source in a direction that corrects distortion using the M detection output.

As explained above, according to the present invention, the AM component generated by the amplitude characteristics of the single-tuned circuit included in the phase shifter is detected, and the gain of the multiplier is controlled by the signal obtained by the AM detection. To obtain an FM detector in which the linearity of detection characteristics is improved and the distortion characteristics are improved by using a single tuning circuit that only requires adjusting one coil without using double tuning which is troublesome to adjust. be able to.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing an example of a conventional Ford Lacher detector, Figure 2 is an equivalent circuit of the phase shifter in Figure 1, and Figure 3 shows the input/output characteristics of the phase shifter in Figure 2. The graph shown in Figure 4 is the first
FIG. 5 is a block diagram showing the detector according to the present invention, and FIG. 6 is a graph showing the detection characteristics of the detector shown in FIG.
A graph showing the detection characteristics of the detection circuit; FIG. 7 is a graph showing the characteristics of the detector according to the present invention in comparison with that of a conventional example;
and FIG. 8 are circuit diagrams showing a specific circuit example of a detector according to the present invention. 1... Phase shifter, 3... Multiplier, 5...
...AM detection circuit. Patent applicant: Pioneer Corporation Figure 2 Figure 3 Original number for Kai-g No. 40 - fO+ Input signal river wave number

Claims (1)

[Claims] A Fordratch detector which adds an FM intermediate frequency signal obtained at the output of a phase shifter having a single tuning circuit and the original intermediate frequency signal to a multiplier, and obtains an FM detection output signal at its output. . A Fordratch detector, characterized in that an AM component generated by the amplitude characteristic of the single tuned circuit is detected, and a gain of the multiplier is controlled by a signal obtained by this AM detection.