JPH03220806A - Self-exciting oscillation circuit - Google Patents

Abstract

PURPOSE:To eliminate the need for an excess level shift circuit and to reduce the power consumption by inputting a 1st voltage signal having a 1st DC level and a gain signal having a 2nd DC level to a gain control converter to which the 1st and 2nd DC levels are set. CONSTITUTION:A 1st voltage/current converter 15 having a level shift stage converts an output signal of a vibrator 10 into a 1st current signal and gives it to a 1st current/voltage converter 16. The 1st current signal is converted into a 1st voltage signal V01 fixed to the 1st DC level. Then square of the V01 is operated by a square computing element 17 having a level shift stage in the opposite direction to output a 2nd current signal 12 and the current 12 is converted into a 2nd voltage signal V02 fixed to the 2nd DC level by a 2nd current/voltage converter 18. Then a gain control converter 20 controls the loop gain of the oscillation loop to be the unity with a gain signal with respect to the V01 and the result is outputted to a vibrator as an exciting signal.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a self-excited oscillation circuit that measures physical quantities such as differential pressure by causing self-excited oscillation using a vibration sensor, and particularly relates to a self-excited oscillation circuit that measures physical quantities such as differential pressure. This invention relates to a self-oscillation circuit that has been improved to enable wide-band self-oscillation.

Such self-excited oscillation circuits can be applied to signal transmitters with limited power usage, such as two-wire signal transmitters that transmit circuit power and signals with a unified current using two transmission lines. I can do it.

<Prior Art> FIG. 5 is a block diagram showing an example of the configuration of a conventional self-oscillation circuit.

Reference numeral 10 denotes a resonator, to which an excitation voltage Ve is supplied from the variable gain amplifier 11, and an output voltage generated at its output terminal by supplying this excitation voltage Ve is the output voltage of the amplifier 1.
Input voltage V at the input terminal of 2.

is entered as . The output voltage of this amplifier 12 is supplied to the input terminal of the variable gain amplifier 11.

In this way, the self-sustained oscillation that oscillates at the natural frequency of the vibrator 10 is continued by the positive feedback oscillation loop constituted by the vibrator 10, the variable gain amplifier 11, and the amplifier 12.

In this case, the oscillation voltage is taken out from the output terminal of the amplifier 12 and inputted to the DC voltage converter 13 to convert it into a DC voltage, and this DC voltage is compared with the reference voltage Es+ and the error amplifier 1
4, the error is amplified and supplied to the variable gain amplifier 11, and the gain of the variable gain amplifier 11 is controlled so that the oscillation amplitude is determined by this reference voltage Es+, so that the self-oscillation of the oscillation loop continues. There is.

However, the variable gain amplifier 11, amplifier 12, DC voltage converter, error amplifier 14, etc. used in such a self-excited oscillation circuit usually include an aiI multiplier width amplifier to perform voltage amplification. In this case, since most of the elements accompanying the monolithic element are capacitive, zero-voltage amplification lowers the cutoff frequency, creating a wideband amplifier that can amplify up to several hundred KH2 or more with low current consumption of a few μA or less. It is difficult to do so.

Therefore, a circuit mainly based on current amplification is generally adopted instead of voltage amplification.

FIG. 6 is a circuit diagram showing an example of a voltage increasing @rgJ path mainly using such current amplification.

Input voltage Vj is applied between the bases of transistors Q5 and Q6, and the emitters of these transistors Q5 and Q6 are each connected to one end of a resistor RE having the same resistance value, and one end of the other end is connected to the negative power supply - Connected to VEE and constant current 1. It is connected to the other end of the constant current source CC1 that flows.

The collectors of these transistors Q5 and Q6 are connected to the emitters of transistors Q1 and Q4, whose bases are grounded, and to the bases of transistors Q2 and Q3, respectively.

The emitters of transistors Q2 and Q3 are connected to each other,
One end is connected to a negative power supply -VEE, and the other end is connected to a constant current source CC2 that flows a constant current IE. transistor Q
The collector of transistor Q2 is connected to the collector of transistor Q4 and connected to the positive power supply +VCC through a load resistor RL, and the collector of transistor Q3 is connected to the collector of transistor Q and connected to the positive power supply +VCC through the load resistor RL. ing. Then, an output voltage V is generated between the collectors of transistors Q and Q4. , has been taken out.

Next, the operation of the amplifier circuit configured as above will be explained.

Input voltage v9. is applied, a constant current IB is distributed to the collectors of transistors Q5 and Q6.

If the distribution ratio is χ, the overall current is constant at I8, so the collector of transistor Q5 has Inx,
A current (l−χ>rs/) is distributed and flows through the collector of the transistor Q6. Therefore, the input voltage Vi has the following relationship.

χIa-(1-χ) I a =Vr 1/RE...
(1) Due to this current distribution, a difference occurs between the base/emitter voltages of transistors Q and Q4, and a differential voltage VO is generated.

In this case, each distribution current χIQ, (1-χ)Is and the difference voltage Vo are Vo = Vv In [(1-χ)IB/χIa]...
・There is the following relationship (2). However, although the thermal voltage of transistors Q5 and Q6 is assumed to be vT, it will be assumed hereafter that all transistors are formed to have the same thermal voltage for simplicity.

Also, this differential voltage vO is converted into collector currents I2 and I in transistors Q2 and Q3, respectively, but the collector currents I2, I3' and differential voltage V0 at this time are I2/13 = exp (Vl)/ VT)”(
There is a relationship 3).

Using equations (2) and (3), the following relationship is obtained: I2/l3=(1-χ)IB/χIB (1-χ)/χ (4). Therefore, each collector current I2, I3 is (
Considering that the current is distributed by the shunt ratio of 1-χ) and χ, the constant current IE is I22(1-χ)IE...(5)I3=
It is distributed as χIE...(6).

Also, the collector currents 11 and I of transistors Q1 and Q4 are
4, if these t current amplification factors are large, ■1°χIB ... (7) I
4-(1-χ)Is (8).

Output voltage V0. is Vo + =RL [(I+ +13) (I2
+I4)]...(9) Therefore, in equation (9), equation (1), (4
) and (5) to (8), the output voltage ■
. , is Vo + = (RL/RE) [1+
(IE/Ia)]...(I1) is obtained as follows.

<Problems to be Solved by the Invention> However, if an oscillation circuit is constructed using a plurality of such voltage amplifiers that mainly perform current amplification, a wide band can be achieved because it is less susceptible to the effects of parasitic capacitance. Since DC level shifting occurs in many cases, new problems arise, requiring extra level shifting circuitry and increasing ground current consumption.

Means for Accomplishing the Problems> In order to solve the above problems, the present invention provides a system in which an excitation signal is input to a vibrator, the vibrator is excited, an output signal generated by this excitation is detected, and this is amplified by an amplifying means. In a self-excited oscillation circuit that self-oscillates at the natural frequency of the vibrator by applying it as an excitation signal, the amplifying means has a level shift stage and converts the output signal into a first current signal and outputs the first voltage. a current converter, a first current/'converter positive pressure converter for converting the first current signal into a first voltage signal fixed at a first DC level, and a level shift stage having a direction opposite to the level shift stage; The second voltage signal is calculated by calculating the square of the first voltage signal.
a square calculator that outputs a high current signal; and a second square calculator that converts this second current signal into a second voltage signal fixed at a second DC level.
a current/voltage converter, an integrator that compares and integrates the second voltage signal based on the reference voltage and outputs a gain signal, the first voltage signal is based on the first DC level, and the gain signal is based on the first DC level. A gain control converter is provided which controls the loop gain of the oscillation loop to be 1 using a gain signal calculated based on two DC levels and outputs it as an excitation signal.

Function> The first voltage/current converter having a level shift stage converts the output signal of the vibrator into a first current signal and outputs it to the first current/voltage converter, where the first current signal is output to the first current/voltage converter. Signal first! :
a first voltage signal fixed at a current level.

Next, a square calculator having a level shift stage in the opposite direction to this level shift stage calculates the square of the first child pressure signal to output a second current signal, and this second current signal is used as a second current signal. ,' a second DC level fixed by a tortoise pressure transducer.
Convert to voltage signal.

Further, the integrator compares and integrates the second S pressure signal with reference to the reference voltage, and outputs a gain signal.

Then, the gain control converter receives a first voltage signal based on the first DC level and a gain signal based on the second DC level, and oscillates based on the gain signal with respect to the first voltage signal. The loop gain of the loop is controlled to be 1 and output as a wJ@ signal to the vibrator.

〈Performance period〉 FIG. 1 is a block diagram showing the overall configuration of the present invention.

2 is an input voltage input from the output end of the vibrator 10, and this input voltage VL2 is passed through a transformer T1 having a midpoint in the secondary measurement to a voltage / current to the AC voltage ei2 to the converter 15.
is entered as . At the midpoint of this transformer T1 is the first group 4! Voltage VS+ is applied. This voltage/SS converter 5 converts the AC voltage ei2 into an AC current 11 and outputs it to the current/voltage converter 16 at the next stage.

The current/voltage converter 16 is composed of an operational amplifier Q7 to which the first base voltage Vs+ is applied to the non-inverting input terminal (+) and a feedback resistor R1 is connected between the output terminal and the inverting input *(-). An alternating current i is applied to this inverting input terminal (-) to produce an alternating current voltage vo whose direct current level is fixed at the first reference voltage VS+.
Convert to +(=i, R).

This AC heavy pressure VOI has a DC level equal to the first reference voltage VS.
It is set to +, and the square of the AC voltage VOI is calculated and the AC @
It is input to the square calculator 17 which outputs it as a i 2.

The current/voltage converter 18 has a second J at its non-inverting input terminal (+).
! : Quasi voltage VS2 is applied and the output terminal and inverting input @ (-
), a parallel circuit of a feedback resistor R2 and a capacitor C2 is connected between the operational amplifier 0, and an AC current 12 is passed through the inverting input terminal (-) to bring the DC level to the first reference voltage VS2. It is converted into a fixed DC voltage V02 and output.

This DC voltage v02 is inputted to a resistor R3 of an integrator with a capacitor C3 connected between the output terminal and the inverting input terminal (between which the reference voltage vR is applied to the non-inverting input terminal (+),
Here, the reference voltage vQ and the DC voltage V. The gain voltage VG is output so that 2 is equal to 2.

20 is a gain control converter, in which the first reference voltage V
When SI is set, AC voltage VO+ is input, and this AC voltage VO+ is set based on this first reference voltage VS+.
It is converted into an alternating current i3 corresponding to + and output.

In this case, this conversion gain is the gain voltage Vc of the integrator 19
is changed based on the second reference voltage VS2.

The alternating current i3 obtained at the output end of the gain control converter 20 is connected to the second group 21! at one end. Transformer T to which voltage VS2 is applied
2 and is passed as a current signal from the secondary side to the input resistor R9 of the vibrator 10) to generate an alternating current voltage VO2, thereby exciting the vibrator 10.

As described above, self-excited oscillation is sustained by the main oscillation loop composed of the voltage/current converter 15 including the vibrator 10, the current/voltage converter 16, the gain control converter 20, etc. In this case, the amplitude of the self-excited oscillation circuit is maintained constant by a gain signal generation circuit that generates a gain signal, which is composed of a square calculator 17, a current/voltage converter 18, an integrator 19, etc., and stable oscillation is continued. .

Next, a detailed circuit including each block configured as described above will be explained using FIGS. 2 and 3. FIG. 2 is a circuit diagram configuring the main oscillation loop, and FIG. 3 is a circuit diagram configuring the gain signal generation circuit.

First, the details of the circuit of the voltage/current converter 15 in FIG. 2 will be explained.

An alternating current voltage ej2 is applied between the non-inverting inputs (+) of the differential amplifiers A1 and A2, the outputs of which are connected to the bases of the transistors Q+o and Q++, the emitters of which are respectively connected to the differential amplifier A1. and the inverting input terminal (-) of A2, and are connected through a resistor R4.

The emitters of transistors Q1° and Q++ are biased at I8+ by constant current sources CCco and CC4, respectively, and their collectors are biased by constant current 2IBI, respectively.
It is connected to one end of constant current sources CC5 and CC6, and the other ends are both connected to the positive power supply +Vcc.

Second standard constitutional pressure Vs2 (Vs, <VS2<V
CC) level-shifted transistors Q+a and Q1
The emitters of 0 are transistors Q+o and Q++, respectively.
The collectors of transistors Q+2 and Q10 are connected to a current mirror circuit formed of transistors Q+a and Q10, respectively. Then, input voltage VL2 is converted into alternating current i and output from the collector of transistor Q15.

Next, the operation of the voltage/current converter 15 configured as above will be explained.

Input voltage V72 is applied to the non-inverting input terminals (+) of differential amplifiers A and A2;
2 is balanced when the input voltage V is applied to the resistor R4, so the alternating current iχ flowing through the resistor R4 is expressed by the following equation.

i x "Vj 2 /R4=・(11) Therefore, the emitters of transistors Q, ., Ql, each have (I
B1+tχ), (Ia+iχ) emitter current flows,
Assuming that the amplification factor of these transistors is large,
A similar collector current flows through the collectors of these transistors.

On the other hand, the constant 44 current sources CC, , CC, each flow a constant current of 2IB, so the transistors Q,2 and Ql3
The emitters of (fatiχ) and (Ia++l
An emitter current of x) is caused to flow, and a similar collector current is caused to flow to the collector. Transistors Q+2 and Ql3
Since a gallent mirror circuit composed of transistors Q14 and Q+s is connected to the collector of transistor Q15, a collector S current that is a copy of the collector S current (Ia+fχ) of transistor Q+a is passed through the collector of transistor Q15. As a result, the alternating current 11 flowing to the next stage current/voltage converter 16 is i,=2iχ...
・(12) becomes.

Also, since this alternating current i is passed through the resistor R1 of the current/voltage converter 16, the alternating current voltage V generated at its output terminal
For O+, Vo + = l 1R1 = 2 i

In this case, the AC voltage VO+ always operates based on the first reference voltage VS due to the effect of the virtual grounding of the operational amplifier Q7, so the AC voltage V0 cannot be directly input to the gain control converter 20. can.

Next, details of the circuit of the gain control converter 20 will be explained.

The emitters of the transistors Q+ s -Q+ v are connected in common, and this common connection point is connected to a constant current source CCv that flows a constant current IB2 as a bias current.
A first reference voltage VSI is applied to the base of +t.

Transistors (h 8- (h s are configured as a pair of differential amplifiers, their emitters are connected to transistors QC
It is connected to the collector of s. Also, transistor Q2
o and Q2 + are also configured as a pair of differential amplifiers, the emitters of which are connected to the collector of transistor Q+v. And transistors Q+s and Q2
The base of the transistor Qts is fixed to the second reference voltage VS2, and the gain voltage Vc from the integrator 19 is applied to the bases of the transistors Qts and Q2.

The collectors of transistors Q+s and Q20 are each directly connected to the positive lightning source +VcC via a current mirror circuit formed of transistors Q22 and Q23, respectively.

The AC current i3 is transmitted from the collector of the transistor Q2 to the transformer T whose one end is connected to the second reference voltage VS2.
2 and is output to the vibrator 10 from its secondary side.

Next, the operation of the gain control converter 20 with a length of 1 m as described above will be explained.

The minute AC voltage VO that is the output of the current/voltage converter 16
By applying I to the base of transistor Q+s, changes of alternating currents +iy+ and -'1'l+ occur in the collectors of transistors Q+6 and Q+v, or these alternating currents change the transconductance to gIL. Then, it is shown by the following equation.

iy+=gtVo+/2 ---<+4)f, gw-Is 2 /2V7 (15).

Next, when the sum of currents of alternating currents flowing through transistors Q+a and Q+s is applied to each emitter of gain voltage VG to the base of transistor Q+a, then transistor Q , 8 is given by the following equation.

1y2=iy+ /'[1+exp (VG/VT)
(16) This emitter S flow iy2 simultaneously flows from the collector as collector To a + i y 2.

On the other hand, whether the collector current iy2 of transistor Q+6 flows through the collector of transistor Q1g with a decrease in collector current iy2 equal to the increase in collector current iy2 of transistor Q+6, or this collector current -1y2 flows through transistor Q2 of the current mirror circuit.
This current is copied to the collector of transistor Q23 and flows as collector current -1y2. As in the case of transistors Q+8 and (hs), a collector current of +iy2 flows through the collectors of transistors Q20.

Therefore, the alternating current i3 is 13=2iy2...<17>.

Substituting equations (14) and (16) into this equation, j:i = g
11v01 / [1+exp (VG /VT)]
−(18). Therefore, the alternating current i3
The magnitude of is controlled by the gain voltage Vc.

Next, details of the gain signal generation circuit shown in FIG. 3 will be explained. The gain signal generation circuit includes a square calculator 17, a current/
Although it is composed of a pressure converter 18, an integrator 19, etc., the details of the circuit of the square calculator 17 will be explained first.

Transistors Q2 a and Q25 are configured as a pair of differential amplifiers, and their emitters are connected to a current source CC through which a constant current IB3 flows. Also, transistor Q
2 e, Q2? are also configured as a pair of differential amplifiers, whose emitters carry a constant current I.

3 is connected to a current source CC9. The bases of transistors Q25 and Q26 are connected to the first reference voltage VS+.
The AC voltage VOI, which is the output of the current/voltage converter 16, is applied to the bases of the transistors Q24 and Q27.

The collectors of transistors Q2a and Q25 are diode-connected transistors Q28 and Q2Q.
, and their collectors are connected to the positive power supply ÷VCC via a resistor R4.

Also, transistors Q3 o and Q3 + are configured as a differential amplifier, and their emitters are connected to transistor Q2
The collectors of transistors Q32 and Q33 are also configured as differential amplifiers, and their emitters are connected to transistors Q32 and Q33.
2? are connected to the respective collectors.

The bases of transistors Q3+ and Q32 are connected to the collector of transistor Q25, and the bases of transistors Q3+ and Q32 are connected to the collector of transistor Q25. and Q
The bases of transistors 33 and 33 are respectively connected to the collectors of transistors Q24.

The collectors of transistors Q30 and Q32 are connected to transistor Q3+ through transistor Q34 of a current mirror circuit composed of transistors Q34 and Q35, respectively.
The collectors of Q33 and Q33 are each connected to the positive power supply +VCC via a transistor Q35. Then, the output alternating current amount a i 2 is taken out from the collectors of transistors Q3+ and Q33.

Next, the operation of the square calculator 17 configured as above will be explained.

The t currents flowing to the collectors of transistors Q2 a and Q25 as a whole are (IQ3〒iz) and (Ia
3 iz), and the transistors Q2g, Q2? As a whole, the $ flow flowing to the collectors of (Ia3
iz), (Ia3 + i2), but the AC voltage V
If only the t flow fluctuation i2 due to OI is considered, iz :gt −Vo 1/ with mutual conductance gt−
2 = (Ia 3 /2VT) Vo + /2...
(19) becomes.

Here, in the same way as when formula (4) was derived, the collector currents of transistors Q2 a and Q2 s (■a3+i
z), (Ia3 tz) and transistor Qco01Q
31, collector current I5 of Qco2 and Qco. I? , I
6. When finding the relationship with Ia, (I s : ” 12
) /'I 83I? ,”' (I B 3
i2)I6/(Ia3 fiz)...
・(20) and (Ia3 iz)/IB 3 I 5 ,・” (I a :l iz
)=I4/' (Ia3 fiz)...
・(21>) In addition, the collector of transistor Q35 is the collector of transistor Q34.
Since it is a copy of the current flow (I5TI6), 1B=I
5+Ig...(22).

Here, if the output S flow is Io, then I o = I a〒Iv Ia I, l + I7 (I5 + Is ) (23) is obtained using the relationship of equation (22).

When the output type aIo is calculated using the above equations (19)2 to (21) and (23), Io = -4iz 2 /Ia 3 , and ■. is the AC current 12 corresponding to the AC quantity pressure VQI
It can be obtained as Therefore, i 2-4 iz '/' I B 3 - <
24). Using the relationship of (one) equation in this equation, i2 = 4 E (Ia3 /'2Vt )VQ
+ /'2]2/' I B 3 Is 3 (VQ + /'2VT) 2... (2
5) It becomes.

Since this AC current 12 flows through the resistor R2 of the current/voltage converter 18, the next DC voltage V02 is generated at its output terminal.

\・′. 2=-i2R2 R2Ia 3' (Vo + /2VT)
(26) Since this DC voltage vo2 operates based on the second reference voltage VS2 due to the virtual grounding of the operational amplifier Q8, it can be input directly to the gain control converter 20 via the integrator 19.

FIG. 4 is a circuit diagram showing another embodiment of the gain control converter.

Transistor Q+a of gain control converter 20 shown in FIG.
.about.Q23 may be constructed as shown in FIG. 4 using multipliers shown as Q30 to Q35 in FIG.

Furthermore, since the transformers T1 and T2 shown in FIG. 2 are used to match the t position between the input and output of the vibrator 10, either one may be omitted, or a capacitive connection may be used.

Note that the @current/'voltage converter 18 may be configured as a rectifier using a peak detection circuit.

<Effects of the Invention> As described above in detail and in detail, according to the present invention, the voltage/
A first voltage signal having a first DC level outputted from the mainstream converter via the first current/voltage converter, and a second voltage signal outputted from the square calculator via the second voltage/current converter. Since the gain signal having a DC level is input to the gain control converter in which the first and second DC levels are set, there is no need for an extra level shift circuit. It is possible to achieve lower current consumption.

Furthermore, since S-flow amplification is effectively used, a wideband self-oscillation circuit can be realized.

Due to these effects, the present invention can be effectively applied to transmitters that have limited power and handle high frequencies, such as two-wire signal transmitters that apply self-excited oscillation.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the overall configuration of the present invention, FIG. 2 is a circuit diagram configuring the main oscillation loop in FIG. 1,
Figure 3 is a circuit diagram configuring the gain signal generation circuit in Figure 1, Figure 4 is a circuit diagram showing another configuration of the gain control converter in Figure 2, and Figure 5 is a circuit diagram of a conventional self-excited oscillation circuit. FIG. 6 is a block diagram showing the configuration of a voltage amplifier used in the self-excited oscillation circuit shown in FIG. 5. 10... Vibrator, 11... Variable gain amplifier, 1 error amplifier, 15... Heavy pressure, 'SS flow membrane changer 168...
・Current pressure converter, 17...Squaring calculator,...Product 5r
20...Gain control converter. Agent＼ Patent Attorney Shinsuke Ko R Diagram 1゛゛〆1

Claims (1)

[Claims] Self-excitation in which an excitation signal is input to a vibrator to excite it, an output signal generated by this excitation is detected, amplified by an amplification means, and applied as the excitation signal to self-oscillate at the natural frequency of the vibrator. In the oscillation circuit, the amplifying means includes a first voltage/current converter having a level shift stage and converting the output signal into a first current signal and outputting the same, and fixing the first current signal at a first DC level. a first current/voltage converter for converting the voltage signal into a first voltage signal; and a level shift stage in the opposite direction to the level shift stage, and calculates the square of the first voltage signal to output a second current signal. a second current/voltage converter that converts this second current signal into a second voltage signal fixed at a second DC level; and a second current/voltage converter that compares and integrates this second voltage signal based on a reference voltage. the first voltage signal is calculated based on the first DC level, the gain signal is calculated based on the second DC level, and the loop gain of the oscillation loop is set to 1 by the gain signal; 1. A self-excited oscillation circuit, comprising: a gain control converter that controls the gain so that the excitation signal is controlled so as to output the excitation signal as the excitation signal.