JPH02279004A - Oscillation circuit - Google Patents

Abstract

PURPOSE:To obtain an oscillator output with less harmonic component independently of use/nonuse of a crystal BPF by connecting input and output of a variable band pass filter(BPF) whose resonance frequency is controlled easily with an external signal and a closing circuit in phase whose gain is the unity or over so as to constitute a VCO. CONSTITUTION:Terminals 15, 19 of a variable filter 20 connect to ground, a terminal 18 is used as an input terminal and a terminal 16 is used as an output terminal to activate a variable BPF 20 and the terminals 18, 16 are coupled with a closing circuit 32 via an amplifier 31 and an output of the amplifier 31 is extracted an oscillated output. Moreover, an external signal is used as a control signal for the variable filter. Thus, the center frequency of the variable BPF 30 is changed in response to the voltage level of an external signal to activate the voltage controlled oscillator(VCO). Thus, the oscillation circuit with high accuracy giving an oscillated output with less harmonic component is obtained.

Description

Detailed Description of the Invention (a) Industrial Application Field The present invention relates to an oscillation circuit that generates an oscillation output having a fixed oscillation frequency, or a voltage-controlled oscillation circuit whose oscillation frequency is variable according to an external signal. Regarding circuits.

(b) Conventional technology Generally, oscillation circuits using ceramic resonators or crystal resonators are used when high precision is required, such as narrowing the pull-in frequency range to 0.5% of the oscillation frequency. be done. Therefore, an example of an oscillation circuit using a crystal resonator will be explained.

As will be described later, this oscillation circuit can be configured with a crystal pantone filter (BPF) and a closed circuit.

First, the principle of the crystal BPF will be briefly explained with reference to FIG. 2. Incidentally, this crystal BPF is disclosed in Japanese Patent Laid-Open No. 121819/1983.

The input signal applied to the input terminal (1) is generated across the emitter resistor (R1) of the emitter follower (T, ), and is connected to a first series circuit consisting of a first resistor (R+) and a capacitor (C+). , is applied to a second series circuit consisting of a second resistor (R1) and a resonant element (x) which is a crystal resonator;
The first and second series circuits form a so-called Wheatstone bridge, and in a balanced state, the first and second transistors (
T, ) (T, ) does not operate, but operates if it is in an unbalanced state, so the output terminal ( 2)
The signal appears. In Figure 2, (÷Vcc
) is the power supply voltage, and the first and second transistors (TI) (
The DC bias for the pace of the emitter follower (Ts) is applied to the first . It is applied through a second resistor (R,) (R,). (T, )(T
s ) is a constant current source transistor and a resistor, and (T
4) A constant bias (V, ) is always applied to the base. (R@) (R?) is the load resistance of the differential pair.

As shown in FIG. 3, the equivalent circuit of the resonant element (x) consists of a series connection component of an inductance (L, ) and a capacitance (C0), and an interelectrode capacitance (C3) component parallel to this component. The impedance of the resonant element (X) becomes zero for a signal at the resonant frequency due to the inductance (L, ) and capacitance (C0), and the balance of the Wheatstone bridge is disrupted. This activates the differential pair and outputs a signal matching the resonant frequency to the output terminal (2). Thus, the circuit of FIG. 2 functions as a band pass filter (BPF).

The frequency characteristic of the crystal BPF having the above-described configuration is a highly accurate PF having a steep peak at the oscillation frequency (f,) of the resonant element (x), as shown in FIG.

Input/output terminals (1) (2) of this crystal B P F (10)
When they are coupled through an amplifier (5) in a closed circuit (6) that is in phase and has a gain of 1 or more as shown in FIG. 5(A), an oscillator with an oscillation frequency of fO is obtained. Furthermore 1. By adding a variable phase shift circuit (7) to the closed circuit (6) as shown in FIG. 5(B), and changing the amount of phase shift of the variable phase shift circuit (7) from the outside using an external signal, The oscillation frequency when the phase difference between the input and output signals of the crystal B P F (10) becomes zero changes from fO, making it possible to function as a voltage-controlled oscillator, so-called vCO.

(c) Problems to be solved by the invention Strictly speaking, a crystal resonator has an odd-order resonant circuit in parallel with a resonant circuit having a resonant frequency (fo), as shown in Fig. 5(B).
Odd harmonics of fo are likely to occur in the output of the VCO, and in order to obtain a clean sine wave, a filter must be added to the output stage to remove harmonic components.

(D) Means for Solving the Problems The present invention provides a VCO by combining the input and output of a variable BPF whose resonant frequency can be easily controlled by an external signal in a closed circuit with the same phase and a gain of 1 or more instead of a crystal BPF. In addition, a variable BPF is inserted into the closed circuit of an oscillator in which the input and output of a crystal BPF are connected in a closed circuit with an in-phase gain of 1 or more, and a variable all-pass filter ( APF) and input the oscillator output to this variable APF.
The phase difference between the input and output of is detected by a phase comparator, and this phase comparison output is fed back as a control signal for the variable BPF and APF,
The configuration is configured so that the phase difference between the input and output of the variable BPF and APF is zero, and the oscillation frequency matches the resonant frequency of the crystal resonator, and an external signal is added to the control signal of the variable BPF to generate the VCO. It is characterized by functioning as

(E) Effects According to the present invention, an oscillator output with few harmonic components can be obtained regardless of whether a crystal BPF is used or not.

(f) Example An embodiment of the present invention will be described below with reference to the drawings.

Incidentally, the same parts as in FIG. 5 are given the same reference numerals, and the description thereof will be omitted. First, referring to FIG. 6, a second-order variable filter (20) that operates as a variable BPF or a variable APF used in this embodiment will be explained.

FIG. 6 is a circuit diagram showing the principle of the variable filter. In FIG. 6, the transistors (T,) (T,) constitute a differential pair, their emitters are both coupled to a constant current source circuit (11), and the collector of the transistor (TI) is connected to the power supply voltage (◆ Vcc) is supplied, and the collector of the transistor (T6) is connected to the constant current source circuit (12), as well as to the terminal (15) via the base of the transistor (T, ) and the capacitor (C7). Note that the current amount of the constant current source circuit (11) is the current amount of the constant current source circuit (12) (
■,) is set to (21+), which is twice that of ).

The transistors (Ty) (TI.) also form a differential pair, their emitters are both connected to the constant current source circuit (13), and the collector of the transistor (TI.) is connected to the power supply voltage (+Vcc).
is supplied, the collector of the transistor (T,) is connected to the constant current source circuit (14), and the collector of the transistor (T,) is connected to the constant current source circuit (14).
, ) and the terminal (1
8). Also, transistor (TI.)
A terminal (19) is connected to the base of. Note that the current amount of the constant current source circuit (13) is set to (21 g), which is twice the current amount (I) of the constant current source circuit (14).

The transistor (T7) forms a pair with the transistor (T8), and a power supply voltage (+VCC) is applied to the collector of each transistor. Further, the emitter of the transistor (T,) is connected to the base and terminal (16) of the transistor (TI) (TI), and the emitter of the transistor (T,) is connected to the base and terminal (17) of the transistor (T,). has been done.

Note that (v,)(v-)(v,)(v,)(v,) correspond to the voltage values of the signals at terminals (15), (16), (17), (18), and (19), respectively. .

Transistors (Ts) (T, ) and transistors (TI) (T, ) of the variable filter (2o) configured as described above
,. ) holds true for the differential pair.

(Vs-Vt)/2re+ = (Vs-V+)
/ 7-... ■〕ωC1 (vs-Vs)/2re* = (V3-V4)
/ , ... ■JωC1 The principle by which this formula ■■ is derived will be explained using FIG. 9.

First, a transistor (Ts) (T
, ) (however, a resistor (RL) is inserted instead of the constant current source circuit (12)), from the characteristics of the differential pair, the collector voltage of the transistor (T6) - (v , ) becomes Vo=gm'RL' (vs-vt) - (a). Here, gm is mutual conductance, q: electric charge per unit, k: Boltzmann constant, and T: absolute temperature.
The relationship 5) holds true. Also, the differential resistance of the differential pair (re,
) kT 1 (= -=-), equation (a) is ql+ 2gm v 6= □ RL ・(vi-■+)
It can be transformed as +++ (c)2re+.

Next, as shown in Fig. 9 (B), the resistance (RL) in Fig. 9 (A) is
If we insert a constant current source circuit (12) with the current amount (■1) instead of , and also insert a capacitor (C1) between the collector of the transistor (T6) and the ground, the constant current source circuit (12) ) can be regarded as infinite, so applying equation (C) to this (B), =
− corresponds to RL, and JωC1 ”°=2re+°city−°(“・−“・)”°(d) holds true.

Next, as shown in Figure 9 (C), connect the capacitor (C3) in (B).
An AC power supply with an output voltage value (vl) is inserted between the
, '), then from equation (d), 7° = ;"3.Z'(Vs-vo)"V+ °
'°(e) holds true.

Next, as shown in Fig. 9(d), considering up to the emitter follower type transistor (T,), and assuming that the emitter voltage of the transistor (T,) is (vo''), in the emitter follower type transistor, v0° = v,'' holds true, so from equation (e), Va =,,,, ``3.Σ'' (Vl-Vl)+
V+...' (f) holds true.

If the part corresponding to the circuit diagram in (D) is extracted from FIG. 6, it will become as shown in FIG. 9 (E), and if we compare (D Spirit=□・=
−・(Vm−v*Dv+ ・・・ (g)2re
+ J61C+ holds true. By transforming this equation (g), equation (2) is obtained.

Similarly, for the differential pair formed by the transistors (TI) (TI.), equation (2) can be obtained using the same derivation method as described above. However, transistor (TI) (T,.)
The differential resistance of the differential pair is (Res).

In the formula ■■, if we eliminate V as Jω=S, we get S1°4rel re c+czV++s・2re*c
t °V4"Vs=(S"・4re+re*C+C*"
S・2re*Ct+1)Vt...' Equation (2) is obtained.

In this formula (3), v+ +Vl+ V1+ V4,
(2) By providing each condition as described below, it is possible to change the characteristics of the variable filter shown in FIG. 6.

(Condition 1) y, = y, = Q, V 4 = V l a, vl = Vll
@1 type■ is S°2re Cao C mushroom°V Im = (S” ・4re
+ retc+c weight◆S゛2retcr+1)°V 0
．． Electricity Vowl/V +*=S°2re snow cm/(S″-4
re, re*c+c mushroom+s°2reffic1÷1) where ωo= (1/4re, retc, cs)””=1(I
mountain/C+cs)""kT Q = (re+C+/re1cm)""= (I, cl
/l1cl)"". This equation (■) indicates the transfer function of BPF.

Therefore, when condition 1 is satisfied, that is, terminals (15) (19
) is grounded, the terminal (18) is the input terminal of the variable filter (20), and the terminal (16) is the output terminal.
The variable filter operates as a variable BPF.

Here, ω0 is the center frequency of the BPF, which changes by changing the current amount (211) (21m) of the constant current source circuits (11) (13). Further, Q indicates the steepness of the filter, and similarly changes by changing the amount of current (21+) (21m). That is, by controlling the current amount (1+) (Is), the characteristics of the variable BPF can be changed.

(Condition 2) V+=Vs=V Is v, = −V +,
l/l:: VoII + From the formula ■... ■ (ω., Q are the same as above). This equation (2) indicates the APF transfer function.

Therefore, when condition 2 is satisfied, that is, terminals (15) (19
) as a common input terminal, inputting a signal with the opposite polarity of the input signal to the terminal (18), and using the terminal (16) as the output terminal, the variable filter (2o) in Fig. 6 can be configured as a variable AP.
It operates as F, and its characteristics depend on the amount of current (11).

(Condition 3) ■, =v, = V 1m, v4=0, v1=v, 1 equation■
From V a, / V Im= (S”◆ω.”)/(S”+
-S. ')...■. This equation (2) represents the transfer function of the band elution filter (BEF).

Therefore, when condition 3 is satisfied, that is, terminals (15) (19
) as a common input terminal, terminal (18) as the grounding terminal, and terminal (16) as the output terminal to create a variable filter.
(20) operates as a variable BEF, and its characteristics depend on the amount of current (11) (+1).

(Condition 4) Vl = V l a, y+ = y, = Q, Vt = V*u+
From formula ■, v a −l/v +, = 'S''/(
S ” + し S ten ma')... ■Q
It becomes Q. This formula ■ is a second-order bypass filter (HPF)
shows the transfer function of

Therefore, when condition 4 is satisfied, terminal (15) is used as an input terminal, terminal (1B) (19) is grounded, and terminal (16) is
) as the output terminal, the variable filter (20)
operates as a HP F, and its characteristics are the current amount (11) (
+1).

(Condition 5) V+=V+= O* Vs= V 16% Vt= V
From out formula ■ ve+++/ V Is”ωO”/ (S”-5”!+
l@”) ... (2) This equation (2) indicates the transfer function of a second-order low-pass filter (LPF).

Therefore, when condition 5 is satisfied, terminal (19) is used as an input terminal, terminals (15) and (18) are grounded, and terminal (16) is
) as the output terminal, the variable filter (20
) operates as an LPF, and its characteristics are the current amount (I,) (
It depends on

As mentioned above, by applying various conditions to the variable filter (20) shown in FIG. 6 without changing its circuit configuration, it can be operated as a variable BPF or variable APF, and the characteristics of the filter can be changed. is the amount of current (It)
(Ig).

Figure 7 is a circuit diagram of a specific variable filter that can control the amount of current (1,) (It) by applying the principle of the variable filter (20) in Figure 6, and uses a constant current source circuit. It is constituted by an emitter 7 oror type transistor and a resistor, and is configured so that the amount of current of this constant current source circuit is controlled according to the voltage value of a control signal. Here, the circuit diagram shown in FIG. 7 will be briefly explained. In FIG. 7, the same parts as those in FIG. 6 are designated by the same reference numerals, and the explanation thereof will be omitted.

The constant current source circuit (11) includes transistors (T,
, ) (T, , ) and a resistor (22) with a resistance value (r), and a transistor (Tz) (Tit) nohes In
A control signal supplied to terminal (5o) is applied. Further, the constant current source circuit (13) also has parallel-connected transistors (Tl
l) (T, 4) and a resistor (23) having a resistance value (r), and a control signal is applied to the base of the transistor (T, , ) (T, , ). In addition, in Fig. 6, the current amount of the constant current source circuits (11) and (12) is (2L +) (2I
t), but as described later, the voltage applied to the base of the transistors (TI) (T, ) of the differential pair is set to the voltage dividing resistor (R
1) By setting the voltage division with (R4) and (R, ) (R1), each constant current source circuit (11) (12) in Fig. 7
The amount of current in the portion corresponding to is set to be equal.

The constant current source circuit (12) includes a transistor (T1.) (T,
4), a constant current source circuit consisting of an emitter 7-oror type transistor (T, , ) coupled to this transistor (T, , ), and a resistor (24) with a resistance value of (2r). Transistor (Ti
The amount of current is controlled according to a control signal applied to the base of t). Similarly, the constant current source circuit (14) is a current mirror circuit consisting of transistors (T, I) (Tll), a transistor (T, .) and a resistor (25
) is replaced with a constant current source circuit consisting of a transistor (
T. ) The amount of current is controlled according to a control signal applied to the base of the Note that the amount of current flowing through the constant current source circuits (11) (12) (13) (14) in response to a control signal having an arbitrary voltage value, that is, the resistors (22) (24) (23) (2
5) t ij! If the amount of current in the resistor (24) is i, the amount of current in the resistors (22) and (23) is 2i, and the amount of current in the resistor (2
5), l flows, and due to the operation of the current mirror circuit,
The collector current of the transistor (T,,) (T,) is also i. Also, the resistors (R1) (R1) (R3) (R1) are inserted to set the gain. Furthermore, although the resistor (R*) (R4) is grounded, a DC bias such as 1-Vcc is applied so that the differential pair can handle high-frequency AC signals when actually operating the circuit. Sometimes you have to.

In the circuit of Fig. 7, if we perform the same calculation as in equation (2), then the following holds true, and when we eliminate V, we get 514re+remC+C*-v,+S・2re,C5
L-v4+L-vs= (S”・4re+re*C+C
*+S・2retC*+L)vt −■.

Applying the condition l to this formula ``'' and making it m6''(L/4re+re*C+Cm)'', it becomes the following, which becomes the transfer function of BPF.

Moreover, when condition 2 is applied to the formula ■°, it becomes the following, which becomes the APF transfer function. In addition, in Figure 8, the variable filter (20) is connected to two operational amplifiers (41) (42).
FIG.

Next, an oscillation circuit created using the variable filter (20) having the above configuration will be described. Figure 1 shows a variable BPF (30
), and the terminals (18) and (16) are connected in a closed circuit (32) via an amplifier (31) to generate an amplifier (
31) Take out the output as an oscillation output and further output the external signal (
By using SG) as the control signal for the variable filter shown in Figure 7, the voltage level B can be adjusted according to the voltage level of the external signal (SG).
The center frequency (ω.°) of P F (30) changes to operate as a voltage controlled oscillator (VCO).

The vCO shown in Fig. 1 can be realized with an extremely simple configuration, but in order to realize an even more accurate VCO, it is necessary to replace the variable phase shifter (7) of the conventional VCO shown in Fig. 5. hand,
Using the variable BPF (30) that satisfies condition 1, condition 2 is applied to another variable filter (20), that is, terminals (15) and (19) are made common input terminals, and terminal (18)
The variable A P F (33
) is possible by adding an automatic control circuit using variable B P F (30). FIG. 10 shows this high precision CO.

In this FIG. 10, the crystal B P F (10) is the same as in FIG. 5, and this crystal B P F (10
) output is input to variable B P F (30). That is, the output of the crystal BPF (30) will be input to the terminal (18) of the variable filter (20) that satisfies condition l, and the terminal (16) of this variable filter (20) will be input to the terminal (16) of the amplifier (31). Coupled to the input end, variable B P F
(30) The output is input to the amplifier (31). The output of this amplifier (31) is output as an oscillation output, and is also fed back to the input end of the crystal BP F (10) in a closed circuit (6).

On the other hand, the variable filter (20
) is another variable filter having the same configuration as variable A
The output of the amplifier (31) is also input to P F (33). The amplitude of the variable A P F (33) is constant regardless of the frequency, and the phase difference between input and output can be set to O (zero) only at a resonant frequency that is controlled from the outside. Therefore, variable A P
The input and output signals of F (33) are transferred to a phase comparator (34).
The phase difference between the input and output of the variable A P F (33) is detected, the phase difference detection signal corresponding to this phase difference is integrated by the low pass filter (LPF) (35),
It is fed back to P F (33) as a control signal. This L
P F (35) output is the variable filter (
20) will be supplied to the terminal (50) of the variable A
The intermediate frequency (ω. The oscillation frequency always matches the oscillation frequency of the oscillation output from 31).

The variable B P F (30) is the variable A P
Since it has the same circuit configuration as the variable APF (33), the control signal to the variable APF (33) is changed to the variable B P F (30
).

That is, the L P F (35) output is changed to the variable B P F (
By also feeding back to the terminal (50) of the variable filter (20) that operates as
The resonant frequency of (30) also matches the oscillation frequency of the oscillation output, and at this frequency, the input/output phase difference of variable B P F (30) also becomes zero, and the oscillation frequency is the resonant frequency of the crystal resonator (fO) Therefore, harmonic components are removed.

Then, an external signal (SG) having a frequency sufficiently higher than the cutoff frequency of L P F (35) is
By adding the control signal that is the output of F (35) to the adder (36), the intermediate frequency of the variable B P F (30) changes, and the crystal B P F (10) changes accordingly.
The intermediate frequency of is also shifted from (fo), and the oscillation frequency can be changed.

In this example, variable B P F (30) and variable A
Two variable filters with the circuit configuration shown in Figure 7 are required for the PF (33), but if they are made with the same monolithic IC, the temperature characteristics will be the same and the relative accuracy of the capacitor and transistor will be good. , the automatic control of the variable APF for the variable BPF has become highly accurate, and although the variable BPF itself has large errors in terms of temperature and absolute accuracy variations, the operation of the variable APF in the same IC allows for the same resonance as the variable APF. becomes the frequency.

(G) Effects of the Invention As described above, according to the present invention, it is possible to realize a highly accurate oscillation circuit that generates an oscillation output with few harmonic components.

[Brief explanation of drawings]

1, 6 to 10 relate to embodiments of the present invention,
Fig. 1 is a circuit block diagram of one embodiment, Fig. 6 is a principle diagram of a variable filter, Fig. 7 is a circuit diagram of a variable filter, Fig. 8 is a circuit diagram of a variable filter configured using an operational amplifier, and Fig. 9 is a circuit diagram of a variable filter constructed using an operational amplifier. The figure is an explanatory diagram explaining the operating principle of the variable filter, and FIG. 10 is a circuit block diagram of another embodiment. FIG. 2 is a circuit diagram of a crystal BPF, FIG. 3 is an equivalent circuit diagram of a resonant element, FIG. 4 is a frequency characteristic diagram of a crystal BPF, and FIG. 5 is a circuit block diagram of a conventional example. (30)...Variable BPF, (33)...Variable APF
, (34)...phase comparator

Claims (3)

[Claims] (1) Variable B whose resonant frequency can be controlled according to external signals
A voltage-controlled oscillation circuit configured by connecting the input and output ends of a PF in a closed circuit with the same phase and a gain of 1 or more. (2) BPF using a vibrator that vibrates at a predetermined frequency
In an oscillation circuit configured by coupling the input and output terminals of the oscillator in a closed circuit having the same phase and a gain of 1 or more, the oscillator is inserted into the closed circuit,
A variable BPF whose resonant frequency can be controlled by a first control signal, a variable APF to which an oscillation output is input and whose output phase can be controlled by a second control signal, and a phase difference between the input and output of the variable APF is detected. and a phase comparator, which feeds back the phase comparison output as the first and second control signals, and sets the input and output of each of the variable BPF and the variable APF to be in the same phase, thereby changing the oscillation frequency to the oscillation frequency of the vibrator. An oscillation circuit characterized by matching the vibration frequency of. (3) BPF using a vibrator that vibrates at a predetermined frequency
In an oscillation circuit configured by coupling the input and output terminals of the oscillator in a closed circuit having the same phase and a gain of 1 or more, the oscillator is inserted into the closed circuit,
A variable BPF whose resonant frequency can be controlled by a first control signal, a variable APF to which an oscillation output is input and whose output phase can be controlled by a second control signal, and a phase difference between the input and output of the variable APF is detected. and a phase comparator, the oscillation frequency of the vibrator is adjusted by feeding back the phase comparison output as the first and second control signals and making the input and output of each of the variable BPF and the variable APF the same phase. An oscillation circuit characterized in that the oscillation frequency is made to match the oscillation frequency and is made variable by adding an external signal to the first control signal.