JPS61270909A - Voltage controlled oscillator - Google Patents

Abstract

PURPOSE:To obtain excellent voltage versus oscillating frequency characteristic even at a high frequency region by forming a variable capacitor on the same semiconductor chip so as to reduce a parasitic inductance thereby eliminating a characteristic distortion at the high frequency. CONSTITUTION:A capacitor 3 on an emitter coupling multivibrator 1 is the result of optional number of selection and combination of plural variable capacitors CO-Cn formed on the semiconductor chip by switches S1-Sn. Further, an adjusting terminal 4 is provided to a differential amplifier 2 to adjust an output voltage amplitude Vx by a value of an adjusting resistor RxX5. Thus, the input voltage versus oscillating frequency characteristic is compensated. An optional capacitance is obtained by operating the switches S1-Sn and it is prevented that the reduction in the degree of freedom of the user's application is fixed by providing an adjusting terminal.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a voltage controlled oscillator (vC○), and particularly to a voltage controlled oscillator suitable for improving distortion in the high frequency region of input voltage-oscillation frequency characteristics. be.

[Background of the invention]

Conventionally, the basic circuit of a voltage controlled oscillator (VC○) is as follows:
“Analog Integrated Circuits” translated by Shuji Nakazawa and two others, Kindai Kagakusha,
There is an emitter-coupled multivibrator type shown in FIG. 6, which is published on September 15, 1975, pages 333-334. As an applied circuit based on the basic circuit,
Generally, the circuit block is as shown in FIG. However, in the applied circuit, the oscillation voltage applied to the capacitor C in FIG. 5 is fixed at VBE (V), but can be set arbitrarily.

The VCO 64 is composed of an oscillation section, a differential amplification section, and an output buffer section, and oscillates the voltage Vin (V) input to the voltage controlled current sources 61 and 62, which have the same characteristics within one oscillation section and the same input terminal. Convert to current I (A), I o: Vin ・・・・・・
(1) The external timing capacitor 63 is charged and discharged with the converted current I based on the 0N10FF state of the transistors 57 and 58, thereby entering an oscillation state. Note that during the oscillation operation, as shown in FIG.

VSTA terminal 50 is in "Loν" state, differential amplifier 5
The voltage at the input terminals 51 and 52 of 9 is IO~II VF"
(V), the voltage amplitude at the output terminal 53.54 of the differential amplifier 59 is ΔV (V), and the voltage difference at the input terminal 53.54 of the differential amplifier 60 is ±ΔV (V).

At this time, the voltage generated at both ends 55°56 of the external timing capacitor 63 has the waveform shown in FIG.
The oscillation frequency f (Hz) according to 4 is as follows. However, C
is the value CF of the external timing capacitor 63), ΔV is the single-end output voltage amplitude (V) of the differential amplifier 59, I is the oscillation current (A) proportional to the input voltage Vin (V), tpd
is the signal propagation delay time (see) caused by element characteristics in the feedback loop between the oscillation section and the differential amplifier section, and generally the external timing capacitor 63 is shorted and the differential amplifier 5
It is equal to one cycle (see) when the VCO 64 is caused to toggle oscillation by reversely connecting the output polarity of 9.

From this, for example, the output voltage amplitude Δ of the differential amplifier 59
V is 0.8 (V), the value C of the external timing capacitor 63 is 50 (pF), the signal propagation delay time tpd is 8 (ns),
When the oscillation current I is 5 (mA'), VC
The oscillation frequency f output from O64 is 25 (MHz
).

In this way, the VCO 64 that changes f (MI4z) according to the value of Vin (V) is 1. For example, in a data discrimination window generation circuit of a magnetic disk storage device, the PLL (P has
The oscillator is used as an oscillator in a locked loop) circuit, but as data transfer speeds have increased recently, oscillation in a higher frequency range is required. Also.

As an oscillator of a PLL circuit, when the input voltage Vin (V) is made equal to a certain reference bias voltage Vo (V),
The oscillation frequency fo (Hz) at that time is determined accurately (for example, ±
(approximately 0.1%) may also need to be adjusted. Note that fo is particularly called a "free-running oscillation frequency", and the oscillation current Io at this time is especially called a "center oscillation current".

In order to meet the above requirements, the VCO 64 has an output voltage amplitude Δ of the differential amplifier 59, which has variations due to manufacturing.
V (V), signal propagation delay time tpd (see), and timing capacitance 6 for external components that have a tolerance of about 1%.
3, the conversion characteristics of the voltage-controlled current sources 61 and 62 are adjusted using external variable resistors, etc., and the center oscillation current I
By changing the value of o(A), a predetermined free-running oscillation frequency fo(Hz
) within the range.

However, with the above measures, the input voltage-oscillation frequency characteristic of the VCO 64 becomes a curve 71 that deviates from the ideal curve 70 shown in FIG. 9 in the high frequency range. This is because in the high frequency range, the constant term tpd that does not depend on the oscillation current I (A) in equation (2) cannot be ignored, that is, [4C
This is because the condition of ΔV/I) >> t pd no longer holds, and the input voltage-oscillation frequency characteristic becomes nonlinear.

Therefore, in order to operate the VCO 64 in a higher frequency range, external components are required such as the value C (F) of the timing capacitor 63 and the single-end output voltage amplitude ΔV (V
) and increase the oscillation current I (A), as well as the signal propagation delay time t pd (
It is essential to improve device characteristics in order to reduce .see).

From the above, similar to the above, for example, the output voltage amplitude ΔV of the differential amplifier 59 is 0.4 (V), the value C of the external timing capacitor 63 is 20 (p F), and the oscillation current I is 5 (m A ).
, in a state where the signal propagation delay time tpcl is reduced to 2 (ns), it is possible to increase the oscillation frequency f output from the VCO 64 to 120 (MH), but in reality, the external connection is Curve 72 where characteristic distortion occurs in a certain frequency range due to the influence of parasitic inductance in lead wires and IC package lead wires.
The input voltage-oscillation frequency characteristic was as follows.

[Purpose of the invention]

The purpose of the present invention is to solve such conventional problems and to develop an emitter-coupled multivibrator voltage controlled oscillator (VCO).
), to provide a voltage controlled oscillator which can obtain input voltage-oscillation frequency characteristics without characteristic distortion in a high frequency range and reduce signal propagation delay time tpd without limiting the range of applications of users. There is a particular thing.

[Summary of the invention]

In order to achieve the above object, a voltage controlled oscillator (v
co)i is a voltage-controlled current source 18.19 that converts an input voltage into a current, an emitter-coupled multivibrator that oscillates based on the N current, and an emitter-coupled multivibrator that amplifies the output of the oscillation and supplies a negative signal to the emitter-coupled multivibrator. In a voltage controlled oscillator in which a feedback differential amplifier 2 is formed on a semiconductor chip,
A plurality of capacitors CO” formed on the semiconductor chip
It is characterized by comprising a variable capacitor 3 made of Cn, which performs the oscillation by charging and discharging the current, and a terminal 4 for adjusting the voltage of the negative feedback.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a voltage controlled oscillator (VC) showing an embodiment of the present invention.
It is a block diagram of O). In the same figure.

11.12 are diodes with equal characteristics, 13°14
are resistors with equal characteristics and low resistance, 15° and 16 are NPN transistors with equal characteristics, 17 is a differential amplifier with positive and negative input/output terminals, 18.19 is a common input terminal 9 a current-drawing voltage-controlled current source with
are the positive and negative input/output terminals and the aforementioned VSTA terminal 50.
A differential amplifier is equipped with a switching input terminal VsTA6 which can similarly instruct start/stop of oscillation operation, and an adjustment terminal 4 to which a resistor 5 is connected to adjust the input voltage-oscillation frequency characteristic aWi, and 3 is a variable capacitor. 10.26 is a DC bias power supply VccyV, which is formed on the same semiconductor chip with a configuration that allows the capacitance value to be changed.
Power supply terminal that supplies EE.

7.8 is an output terminal for sending out differential signals of opposite polarity from the differential amplifier 17 to the outside, and 20 to 25 are connection terminals.

The circuit configuration of the VCOL is as shown in No. 111, in which the anodes of diodes 11 and 12 and one end of resistors 13 and 14 are connected to the mg terminal vccto, and the opposite side, that is, the cathode of diode 11 and the other end of low resistance resistor 13, are connected to the mg terminal vccto. Connect end to end 2
0 to the collector of the NPN transistor 15 and the positive input terminal of the differential amplifier 2, and connect the cathode of the diode I2 and the other end of the resistor 14 to the NPN
Connected to the collector of the N transistor 16 and the negative input terminal of the differential amplifier 2.

Similarly, the positive output end of the differential amplifier 2 is connected to the positive input end of the differential amplifier 17 and the base of the NPN transistor 16 via the connecting end 22, while the negative output end is connected to the connecting end 22.
3 to the negative input terminal of the differential amplifier 17 and the base of the NPN transistor 15. NPN) - the emitter of the transistor 15 is connected to the output end of the voltage controlled current source 18 and one end of the variable capacitor 3 via the connection end 24;
On the other hand, the emitter of the NPN transistor 16 is connected to the connection terminal 25.
It is connected to the output end of the voltage controlled current source 19 and the other end of the variable capacitor 3 via. The positive and negative output terminals of the differential amplifier 17 are connected to output terminals 7 and 8, respectively, and voltage control and current source L8 are connected.
．． The other end of the output of L9 is connected to the DC bias power supply VEE, and the common control input end of the voltage controlled current source 18 and 19 is connected to the input terminal 9.
Then, the amplitude adjustment terminal and the switching input terminal of the differential amplifier 2 are connected to the adjustment terminal 4 and the switching input terminal 6, respectively. A resistor 5 for voltage adjustment, which will be described later, is connected to the adjustment terminal 4. Note that each of the above elements except the resistor 5 is formed on the same semiconductor chip.

The VCOl performs an oscillation operation using the same oscillation mechanism as the VCO64 shown in FIG.
) is sent to output terminals 7 and 8. Its oscillation frequency f(H
z) is the same as in equation (2) above. However, CX has variable capacity! a3 value CF), vX is the single-end output voltage swing * (V) of differential amplifier 2, tpd is the signal propagation delay time (sec), and Δ is the oscillation current (A) proportional to the input voltage Vin (V). be.

The difference from the VCO 64 described above is that (1) a resistor 5 for adjusting vx is connected to the differential amplifier 2, and (2) a variable capacitor 3 is formed on the same semiconductor chip.

FIG. 2 is a configuration diagram of a variable capacitor 3 showing an embodiment of the present invention. In the same figure, col CL *C2r
C3...Cn are capacitors formed on the same semiconductor chip with values to be described later, and Sl is a capacitor formed on the same semiconductor chip.

S2+S3...Sn are switching devices that can be set to an open or short-circuit state, respectively.

The capacitor C□''Cn sets the value Cx(F) as the variable capacitor 3 to the minimum C)(win(F) when all switches wI81 to Sn are in the open state, and conversely, all are in the short-circuited state. When this happens, the maximum value is CXmax (P).This can be expressed as a formula.

Cx+*1n=C(I X(1+a) ””
(4)C)<max=(C□ +C1+C2+”・+C
n)

In addition, the capacitor Co''Cn is set to the value Cx(F) of the variable capacitor 3 to the target value CTc(F).

Co = CT c/ 2 (F) ”(6
3C1=CTc/2CF) ...(7
)C2=CT C/22CF) ""
(8) Cs = CT c/23(F)
”(9)Cn=+CTc/2'(F)
-...cto).

C) (min (F) and C) (may (F) when configured in each of the above parts are calculated from the above formulas (4) and (5),
)＜+ain=CT CX(1+ a)/2 (F)
...(11)=CTcX[(3/2) (1/
2”)×(1+α)(F) 5 (12) In other words, the value Cx(F) of the variable capacitor 3 is set to (1
1) Value C according to formula (+m1n(F) to value C according to formula (12)) (max(F)), each switch 81
By opening or shorting ~Sn, CTC
(1+α)/2nCF) allows setting an arbitrary capacitance value. In other words, as shown in Figure 4, the adjustment range when manufacturing variation α = 0 is 0.5.
(,rc~[1,5(1/2')ICT(:(F'),
The adjustment range is 0.6C7c when the setting pitch is CT (:/2'CF) and manufacturing variation α; +20%.
~(1,8-(1,2/2')JCrc(F)-Setting angle f FC1,2 CT (:/2" (F) Adjustment range when manufacturing variation α=-20% 0.4CT~(1,2(0,8/2”)]CTC(
F), the setting pitch is 0.8 (, rc/2" (F). Therefore, by using one piece, the manufacturing variation can be reduced by ±2.
The value CX(F) of the variable capacitor 3 at 0% is set to the minimum value 0.
Maximum value from 6Crc(F) [1, 2 (0, 8/2”l)]
Up to CTc (F) (7) from medium to maximum Wf4M (1,
2/2 n””) CTa(F) (7) Can be set arbitrarily at 11th place.

From the above, for example, when the number of stages n is set to 6'',
Cx(F) from the range of 0.6CTc to 1.19CTc(F), the maximum error is 0.0094CTC(F) (=0.
94%) can be set arbitrarily. Also.

If the manufacturing variation is ±30% and the number of stages n is the same as above *"6'J: L7'= then LC4:l:, Cx(F
) wo 0, the maximum error is 0.0 from the range of 65CTC to 1.039CTc(F). Can be arbitrarily selected using the value of OL 02CTG (F).

FIGS. 3(a) to 3(c) show examples of realizing open or shorted states of the switches S1 to Sn.

In the same figure (a), between terminal TI and 'r3, terminal 'r
By passing a large current between 2 and T3, the junctions of diodes DSly and DS2 are destroyed,
This is a method of changing the state between the terminals 'r and -'r2 from open to short-circuited. In the same figure (b), by flowing a large current between terminals 'r and -'r, fuse (1st) is blown, and terminals 'r and -T2 are changed from a short circuit to an open state, contrary to the above. This is the way to do it. In the same figure (e), the terminal T1
This is a method in which the metal wire connecting between -T2 is irradiated with a laser beam to fuse it, and the terminal 'r and -T2 are changed from a short circuit to an open state as in the above 1a (b).

FIG. 5 is a circuit diagram showing one embodiment of the differential amplifier 2. In FIG. In addition, in the same figure, the connection end 20~23° resistor RX5
．． Adjustment terminal 4. Switching input terminal 6. The illumination bias power supplies VEE are the same as those shown in FIG. 1 above.

When the signal VSTA from the switching input terminal 6 is at 1 "High" level, the differential amplifier 2 turns on the transistor Tr5 to stop the amplification function, and vice versa.
When the voltage is at the v37 level, T r 5 is turned off to perform the amplification operation. Moreover, since the emitter voltage of the transistor T r 5 can be changed according to the value of the adjustment resistor RX5, the output voltage amplitude Vx (V) of the connection terminal 22 and the connection terminal 23 can be changed to Ill! It is possible to do so.

The single-ended output voltage amplitude of the differential amplifier 2 due to its adjustment Vx (V month, V x ” (Rs / (Rt + Rx) 3X
(VER-VBE)(V)'' (13) Note that in this embodiment, the variable resistor 5 is externally connected to the adjustment terminal 4.

It is also possible to connect a circuit network having a temperature compensation function or the like.

In this way, by forming the variable capacitor 3 on the same semiconductor chip with a W1 degree equal to or higher than that of individual components, the parasitic inductance associated with wiring etc. can be made extremely small, and the high frequency of the input voltage-oscillation frequency characteristic can be minimized. It becomes possible to remove characteristic distortion in the area. In addition, the variable capacitor 3 (
6) to (10), and by providing switchers 81 to Sn for connecting them, the value Cx(F) of the variable capacitor 3 can be changed. It is possible to easily and accurately set the target value Crc (F), and the timing capacity was previously set to 63.
Since the m'M resistor 5 connected to the differential amplifier 2 compensates for the input voltage-oscillation frequency characteristics, it is possible to prevent the user's flexibility in application, which would be reduced if the timing capacitance was fixed. can.

〔Effect of the invention〕

As explained above, according to the present invention, parasitic inductance is significantly reduced by forming variable capacitors on the same semiconductor chip, characteristic distortion in the high frequency range is eliminated, and signal propagation delay time tpd is also reduced. Since it is small, good input voltage-oscillation frequency characteristics can be obtained even in a high frequency region of several tens of Mz or more. Further, by configuring the variable capacitor with a plurality of capacitors having different values, the user's range of application is prevented from being limited.

[Brief explanation of the drawing]

FIG. 1 shows a voltage controlled oscillator (V
CO), FIG. 2 is a block diagram of the variable capacitor r) 3, FIGS. 3(a) to (c) are diagrams for explaining how to realize the switching devices 81 to Sn, and FIG. Value of capacitor 3 Cx(
Fig. 5 is a circuit diagram of the differential amplifier 2, and Fig. 6 is a diagram for explaining the setting method of the differential amplifier 2.
○) Circuit diagram showing the basic circuit, Figure 7 is the conventional voltage side m
FIG. 8 is an equivalent block diagram of an application circuit of an oscillator (VCO), FIG. 8 is an operation timing chart of FIG. 7, and FIG. 9 is a characteristic diagram of input voltage versus oscillation frequency of FIG. 7. 1.64: Voltage controlled oscillator (VCO), 2,17°59
．． 60: Differential amplifier, 3: Variable capacitor, 4: '111M
Terminal, 5*131 14 r RL~R4: Resistor, 6: Cut-off input terminal, 7, 8: Output terminal, 9: Input terminal, 10.26: Power supply terminal, 11, 12. Dsl *D
s2: Diode, 15, 16, 57, 58°Trl~
Tr5: NPN transistor, 18.19°61.62: Voltage controlled current source, 20~25.51~54
: connection end, 50: VSTA terminal, 55, 56; external terminal, 63: external timing capacitor, 70: ideal characteristic curve,
71, 72: Characteristic curve, T1 to T3: Terminal, C (1”
Cn: Capacitor, Hsl: Fuse, 81-Sn: Switch. Figure 1 Figure 2 Figure 4 Figure 5

Claims (1)

[Claims] (1) A voltage-controlled current source that converts an input voltage into a current, an emitter-coupled multivibrator that oscillates based on the current, and a differential amplifier that amplifies the output of the oscillation and provides negative feedback to the emitter-coupled multivibrator. in a voltage controlled oscillator formed on a semiconductor chip, the voltage controlled oscillator is composed of a plurality of capacitors formed on the semiconductor chip, and includes a variable capacitor that performs the oscillation by charging and discharging the current, and a voltage of the negative feedback that is adjusted. A voltage controlled oscillator characterized by comprising a terminal for.