JPS6023525B2 - Quadrature type detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a quadrature detection circuit suitable for FM detection.

2. Description of the Related Art Conventionally, a quadrature detection circuit configured as shown in FIG. 1 has been known as an FM detection circuit used in FM receivers and the like.

In other words, the FM (IF) signal from the FM (IF) signal source Vg such as the IF stage is passed through the differential amplifier circuit DA2 consisting of transistors Q, , Q2, and then to the lower stage differential amplifier circuit DA2 consisting of transistors Q3 and Q. A double-balanced differential amplifier circuit D having an upper stage differential amplifier circuit D consisting of transistors Q to Q.
The signal is supplied to a quadrature type detection circuit Q-DET consisting of a BA and an LC tuning circuit T.

Then, the quadrature type detection circuit Q-DET generates a 90° phase shifted wave with the tuning circuit T for the FM input signal,
The height due to the frequency shift of the FM wave appears as a phase lead and lag between it and the 90° phase-shifted wave, so the detection output is determined by the product of these two waves, that is, the increase or decrease in the current that flows when they match in time. This is done by controlling the lower stage differential Taitomi circuit D, which switches with the original FM input signal, to the upper stage differential amplifier circuit D, to which the 90° phase shifted wave is applied. . Therefore, in this case, the phase difference between the signals appearing at the output terminal 2 of the lower differential amplifier circuit D and the input terminal 3 of the upper differential amplifier circuit D is correct.
o must match.

However, the signal at the output terminal 2 of the lower stage differential amplifier circuit D deviates from the signal at the input terminal 1, so in order to compensate for this, an emitter follower transistor Q, is installed on the input side of the upper stage differential amplifier circuit D. By adding Q and o, the signal at the input end 3 of the upper stage differential amplifier circuit ○ is shifted from the signal at the input device 4 of the emitter follower transistor Q9. In such a quadrature type detection circuit D-DBA, 1 is connected to the bases of transistors Q and Q4 of the lower stage differential amplifier circuit DA2.
A phase difference of 80° results.

In other words, it is desirable that the load conditions of the transistors Q, , Q2 of the differential amplifier circuit DA, which receives the step, be the same from the midpoint of the S curve, but an unbalance may occur due to the capacitor C on the load side of the transistor Q2. was. Due to such unbalance and the stray capacitor of each transistor of the double-balanced differential circuit DBA, the deviation between 2-1 and the deviation between 4-3 do not match, resulting in
It was not possible to correct the phase difference between -2 and match the phase difference to 90o. For this reason, there has been a drawback that tuning shift and deterioration of distortion occur, impairing detection characteristics. Therefore, the present invention has been made in view of the above points, and an object of the present invention is to provide an extremely excellent quadrature type detection circuit that can eliminate tuning errors and improve detection characteristics by adding a simple phase correction circuit. The purpose is to

First, to briefly explain the principle of this invention, the above-mentioned 3.
Distortion technique 4 when the interval between −2 and 29 is delayed from
If it goes further than that, it will shift to a lower position.

Since the phase difference between 3 and 2 is usually more than 2900 degrees, in order to correct this phase shift, the above-mentioned double balanced differential amplifier circuit D is used.
This is based on the fact that it is sufficient to add a phase correction circuit that shifts the signal applied to the switching in the lower stage differential amplifier circuit D in BA by an amount corresponding to the phase shift of 3-2. The &phase correction circuit can be constructed by simply adding a phase correction circuit such as a capacitor to shift the phase of the signal to the switching section of the quadrature type detection circuit from that of the signal to the tuning circuit (detection circuit).
The present invention is characterized in that phase correction can be performed simply and reliably, thereby improving the detection characteristics of the quadrature type detection circuit. An embodiment of the present invention will be described in detail below with reference to the drawings.

That is, from the FM (IF) signal source Vg such as the IF stage, the FM
(and) signals are transmitted by transistors Q, . A double-balanced differential amplifier circuit DBA has a lower stage differential amplifier circuit DA2, which is transistors Q3 and Q, and an upper stage differential amplifier circuit DA3, which is transistors Q to Q, via a differential amplifier circuit DA, which is composed of transistors Q2.
Quadrature type detection circuit Q-D consisting of and tuning circuit T
ET.

Here, the FM (IF) signal is a double-balanced rhombus amplifier circuit D.
It is directly supplied to the lower stage differential amplifier circuit D of the SA, and is converted into a 900 phase shifted wave of the original FM (m) signal through the LC tuning circuit T to the upper stage differential amplifier circuit ○. After that, the emitter follower transistors Q,Q,. Supplied via. In addition, the lower stage differential amplifier circuit DA, which serves as the switching section,
The load side of the transistor Q2 that constitutes a phase correction circuit PC between the base of the other transistor Q of No. 2 and the base of the other emitter follower transistor Q, o interposed on the input side of the upper stage differential amplifier circuit DA3. Add a capacitor C equivalent to the capacitor C. In the above configuration, even the lower stage differential amplifier circuit DA2 which switches with the original FM input signal can perform the above-mentioned FM detection by controlling the upper stage differential amplifier circuit D to which a 90o phase shifted wave is added. action is taken.

In this case, the emitter follower transistors Q, Q, o are connected to the input terminal 3 of the upper stage differential amplifier circuit DA3 and the lower stage differential amplifier circuit D.
In order to correctly set the phase difference with the output terminal 2 of A2 to 900, the input/output terminals 4-3 on the upper stage are shifted by the difference between the input/output terminals 2--on the lower stage, but this alone will not actually work. Stray capacitor and capacitor C of both upper transistors
, the deviations between 2-1 and 4-3 do not match, and the phase difference between 3-2 cannot be made to match 290 degrees. However, in this invention, a capacitor C added as a phase correction circuit PC is used to tune a signal to a lower differential amplifier circuit D, which is a switching section of a quadrature type detection circuit Q-DET, to a tuning circuit (detection coil).
By shifting the signal to T by an amount corresponding to the phase shift between 3 and 2, it is possible to compensate for the phase shift due to the stray capacitor, unbalance, etc.

That is, as a result, the phase difference between 3 and 2 can be correctly set to 900. This is because, as explained in the above principle, the minimum distortion point of the so-called S curve given as the FM detection output is 3 - If the phase difference between 2 and 2 lags behind 290, it will shift toward the higher frequency side, and when it advances beyond 2900, it will shift toward the lower frequency, but normally it will deviate between 3 and 2 compared to 900. This is based on the fact that it is sufficient to add a phase correction circuit consisting of a capacitor C to correct this phase shift. It goes without saying that the present invention is not limited to the embodiments described above, and that various modifications can be made without departing from the spirit of the invention. Therefore, as detailed above, according to the present invention, it is possible to provide an extremely excellent quadrature type detection circuit that can eliminate tuning deviation and improve detection characteristics by adding an easy-to-use phase correction circuit. .

[Brief explanation of drawings]

FIG. 1 is a wiring diagram showing a conventional quadrature detection circuit, and FIG. 2 is a wiring diagram showing an embodiment of the quadrature detection circuit according to the present invention. Vg...FM (IF) signal source, DA.・・・・・・
Differential amplification circuit, DBA...Double balanced differential amplifier circuit, DA2...Lower stage differential amplifier circuit, to D...
...Upper stage differential amplifier circuit, Q-DET...Quadrature type detection circuit, T...Tuning circuit, Q9
,Q,. ...Emitter follower transistor, P
C... Phase correction circuit. Figure 1 Figure 2

Claims (1)

[Claims] 1 A differential amplifier circuit consisting of transistors Q_1 and Q_2 receiving the IF stage, a lower stage differential section (switching section) to which the signal for the test wave outputted from the differential amplifier circuit is applied, and a tuning circuit (detection coil). and an upper stage differential section to which a 90° phase wave of the signal to be detected is applied. In order to shift the phase, a phase correction circuit made of a capacitor is added, one end of which is connected to the input end of the upper differential section of the double-balanced differential circuit, and the other end of which is connected to the input end of the switching section. A quadrature type detection circuit.