JPS62135008A - Phase shift circuit - Google Patents

Abstract

PURPOSE:To shift accurately an input signal by 90 deg. and to make the circuit suitable for circuit integration by setting the 1st, 2nd and 3rd resistors in response to the phase shift quantity so as to eliminate a DC bias cut-off capacitor. CONSTITUTION:Output terminals A, B of the 1st and 2nd signal voltage sources 12, 16 are connected through a series circuit comprising resistors R6, R7, and a connecting point C between the resistors R6 and R7 is connected to a base of a transistor (TR) Q1 of a differential amplifier circuit 13. A difference voltage of collector voltages extracted from Trs Q1, Q2 becomes a signal whose phase is shifted from that of an emitter AC voltage v' of a TR Q3 by 90 deg.. That is, a frequency signal generated by the 1st signal voltage source 12 is shifted by 90 deg. and outputted from output terminals 14, 15. Since the phase shift circuit uses no DC bias cut-off capacitor, an accurate phase shift is applied and the circuit is suitable for circuit integration.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a phase shift circuit used in a quadrature detection circuit of, for example, an FM receiver.

[Technical background of the invention and its problems] Conventionally, a quadrature detection circuit is often used as an FM detector in an FM receiver. This quadrature detection circuit inputs a frequency modulated wave whose phase is shifted by 90 degrees by a phase shifter and an original frequency modulated wave to a multiplier, and obtains a demodulated signal from the output beat component. In particular, an LC resonance type phase shift circuit using an inductor and a capacitor C is usually used as the phase shifter. However, this LC resonance type phase shift circuit requires external adjustment and is not suitable for IC implementation.

Therefore, attempts have been made to eliminate the need for adjustment in phase shift circuits, one of which is a circuit as shown in FIG. This phase shift circuit uses a bridge circuit 11 composed of resistors R1 to R3 and a ceramic resonator CF.
One input terminal a of the bridge circuit 1 is connected to the output terminal of the signal voltage source 12, and the other input terminal d is connected to AC ground.

This bridge circuit 11 has R1-R2, and the impedance of the ceramic resonator CF is set to ZS-jXs, so that R3=lZsl. That is, the frequency signal from the signal voltage source 12 is supplied to the input terminal a of the bridge circuit 110, and the potential difference appearing between the connection points A and C of R1 and R2, R3 and CF is extracted by a differential amplifier (not shown). By doing this, it is possible to obtain a frequency signal shifted by about 90 degrees.

However, the conventional phase shift circuit as described above is
In reality, the configuration is as shown in FIG. 4, and there are the following problems. That is, in FIG. 4, transistors Ql, Q2
, resistors R4, R5 and constant current source 11 are a differential amplifier circuit 13.
The drive voltage is obtained from the DC power supply voltage line VCC. Note that the collectors of the transistors Ql and Q2 are connected to the output terminal 14.15, from which frequency signals having a phase of 90° can be obtained.

Further, the other input terminal d (di) of the bridge circuit 11.

d2) is connected to the power supply voltage line VCC as an AC ground. Here, the DC bias of the bases of the transistors Ql and Q2 is supplied by a signal voltage R12, and the resistor R2 is connected to the power supply line VCC via a DC isolation capacitor C1. In other words, this capacitor CI causes the phase to not shift by 90° accurately, and the capacitor C1 requires a large area when integrated into an IC, which is very disadvantageous.

[Purpose of the Invention] This invention was made to improve the above-mentioned problems, and it is possible to eliminate the DC bias isolation capacitor, accurately shift the input signal by 90' phase, and is also suitable for IC implementation. The purpose of the present invention is to provide a phase shift circuit that has the following characteristics.

[Summary of the Invention] That is, the phase shift circuit according to the present invention includes Ml and a second signal voltage that generate a first AC frequency signal and a second AC frequency signal having an opposite phase to the first AC frequency signal. a first series circuit comprising a source, a first and a second resistor connected between the output terminal of the first signal voltage source and the output terminal of the second signal voltage source, and the first signal voltage source; A second series circuit including a third resistor and a ceramic resonator connected between the source and the AC ground, and a connection point between the first and second resistors of the first series circuit are connected to one input terminal. , a differential amplifier circuit in which a connection point between the third resistor and the ceramic resonator of the second series circuit is connected to the other input terminal, and the first, second, and third resistors are connected to each other in phase. It is characterized in that it is set according to the amount of shift.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described in detail with reference to FIGS. 1 and 2. However, in Figures 1 and 2,
The same parts as in FIGS. 3 and 4 are denoted by the same reference numerals, and only the different parts will be described here.

FIG. 1 shows its basic configuration. In this phase shift circuit, the output terminals A and B of the first and second signal voltage sources 12°1G are connected through a series circuit of resistors Re and R7, and the connection point C of resistors R8 and R7 is connected to the It is connected to the base of the transistor Q1 of the dynamic amplifier circuit 13. still,
Here, the collector of the transistor Q1 is denoted by E, and the collector and base of the transistor Q2 are denoted by E and F.

In the above configuration, to explain its operation, first, the output AC of the first and second signal voltage sources 12 and 18 is
Let the voltages be v and -v, and A generated at each connection point A to F above.
Assuming that the C voltage is vA = vP, and the resistance ratio of the resistors Re and R7 is R8:R7-1:n, the following is obtained. Also, if the impedance of the ceramic resonator CF is Zs-jXs (ceramic resonator uses between resonance and anti-resonance), it becomes...(2), and the difference voltage between vD and vE is the difference between vC+vF The voltage is proportional to . Therefore, an arbitrary amount of phase shift can be obtained by setting n and R3.

FIG. 2 shows an actual circuit configuration, in which each frequency signal output from the first and second signal voltage sources 12.16 is inputted to a phase shift circuit through an input terminal 17.18, and further coupled to a phase shift circuit. First and second emitter follower amplifier circuits 19.2 via ring capacitors C2 and C3.
0. First emitter follower amplifier circuit 19
is composed of a transistor Q3, a resistor R8, and a constant current source (2), and the emitter of the transistor Q3 is the connection point A.

Further, the second emitter follower amplifier circuit 20 is composed of a transistor Q4, a resistor R9, and a constant current source I3, and the emitter of the transistor Q4 is the connection point B.

Note that the resistances Re and R7 are set to R6:R7-1:3. Further, the resistor R3 is set equal to the impedance ZS-jXs of the ceramic resonator CF.

That is, when each frequency signal from the first and second signal voltage sources 12.18 is input, the transistors Q3. Each emitter A of Q4
When the C voltage is v-, -v'', the AC voltage VBQ applied to the bases of the transistors Ql and Q2 of the differential amplifier circuit 13 is
I, VBQ21; 1 (from formula 11, it becomes. Therefore, the output voltage of transistors Ql and Q2 v l +
v2 becomes v1jA4v' v2--jA-v-. However, A is determined by the gain of the differential amplifier circuit 13. As can be seen from this, the transistor Q
1. The voltage difference between the collector voltages taken out from Q2 is V'
That is, the frequency signal generated by the first signal voltage source 12 is outputted from the output terminals 14 and 15 with a phase shift of 90 degrees.

Therefore, the phase shift circuit configured as above is D
Since a capacitor for C bias isolation is not used, accurate phase shifting is possible, and it is also suitable for IC implementation.

[Effects of the Invention] As detailed above, according to the present invention, it is possible to eliminate the DC bias isolation capacitor, accurately shift the phase of the input signal by 90'', and furthermore, it is possible to create a phase shift circuit suitable for IC implementation. can be provided.

[Brief explanation of drawings]

FIG. 1 is a basic circuit configuration diagram showing an embodiment of a phase shift circuit according to the present invention, FIG. 2 is a circuit diagram showing an actual circuit configuration of the same embodiment, and FIGS. FIG. 2 is a circuit diagram showing the configuration of a phase shift circuit. 11... Bridge circuit, 12... First signal voltage source, 13... Differential amplifier circuit, 14.15... Output terminal, 1B... Second signal voltage source, 17.18 ...Input terminal, 19.20...Emitter follower amplifier circuit. Figure 1 Figure 2

Claims (1)

[Claims] first and second AC frequency signals that generate a first AC frequency signal and a second AC frequency signal that is in opposite phase to the first AC frequency signal;
a signal voltage source, and first and second signal voltage sources connected between the output terminal of the first signal voltage source and the output terminal of the second signal voltage source.
a first series circuit consisting of a resistor, a second series circuit consisting of a ceramic resonator and a third resistor connected between the first signal voltage source and AC ground; A differential amplifier circuit in which a connection point between the first and second resistors is connected to one input terminal, and a connection point between the third resistor and the ceramic resonator of the second series circuit is connected to the other input terminal. A phase shift circuit, characterized in that the first, second, and third resistors are set according to a phase shift amount.