JPH0730382A - Voltage-controlled oscillator - Google Patents

Abstract

PURPOSE:To adjust the VCO range for an input voltage and to adjust the center frequency. CONSTITUTION:When resistances 45 and 46 are varied, currents I1 and I2 flowing through them vary and a current I3 flowing through a load PMOIS 49 also varies. Once the current I3 is determined, the current I of a constant current charging circuit 60 and a constant current discharging circuit 70 is determined. A capacitor 73 is changed and discharged with the current I and an output voltage Vout of oscillation frequency corresponding to the input voltage Vin is outputted from an inverter 76.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage controlled oscillator (hereinafter referred to as VCO) having a center frequency adjusting function and a voltage controlling oscillator range adjusting function.

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram showing a configuration example of a conventional VCO. The VCO is an oscillator in response to an input voltage V _in is the frequency of the output voltage V _out is controlled, and a constant current circuit 10 outputs a constant current I in response to the input voltage V _in. The constant current circuit 10 includes an operational amplifier 11, an N-channel MOS transistor (hereinafter referred to as NMOS) 12 that controls the current I, a frequency adjustment resistor 13, and a load P-channel MOS transistor (hereinafter referred to as PMOS) 14. It is composed of P
The gate and the drain of the MOS 14 are connected to the gate of the PMOS 15, the source of the PMOS 15 is connected to the power supply voltage VCC, and the drain is the NMOS 16
Is connected to the ground potential GND via. PMOS 1
A constant current charging circuit 20 is connected to the gates 4 and 15, and a constant current discharging circuit 30 is connected to the gate of the NMOS 16. A capacitor 33 is connected to a connection point N between the constant current charging circuit 20 and the constant current discharging circuit 30. The Schmitt circuit 34 that outputs the charge / discharge switching control signal S34 is connected to the connection point N, and the two-stage inverters 35 and 36 that output the output voltage V _out are connected to the output side thereof.

The constant current charging circuit 20 is a circuit for charging the capacitor 33 with a constant current, and is a switching PMO gate-controlled by the drain voltage of the PMOS 14.
S21 and a PMOS 22 whose gate is controlled by a charge / discharge switching control signal S34, which are provided with a power supply voltage VC
It is connected in series between C and the connection point N. The constant current discharge circuit 30 is a circuit that discharges the capacitor 33 with a constant current, and includes an NMOS 31 gate-controlled by the gate voltage of the NMOS 16 and a switching NMOS 32 gate-controlled by the charge / discharge switching control signal S34. They are connected in series between the connection point N and GND. The PMOS 14, 15, and 21 have a mirror coefficient 1:
It constitutes a 1: 1 current mirror circuit. Also, N
The MOSs 16 and 31 form a current mirror circuit having a mirror coefficient of 1: 1.

[0004] Figure 4 is a characteristic diagram showing the relationship between the input voltage V _in of the VCO of Figure 3 and the oscillation frequency f. VINA is the voltage value of the input voltage V _in, f ₀ is the center frequency. The operation of FIG. 3 will be described with reference to FIG. Input voltage V _in
Is input to the operational amplifier 11, the current control NMOS 12 connected to the output side of the operational amplifier 11 controls the current I flowing through the adjustment resistor 13. Current I, the operational amplifier 11 and _{NMOS12, I = V in / R} 13 ( where, R _13; resistance value of the adjusting resistor 13) is controlled so as to be. Since the load PMOS 14 constitutes a current mirror circuit together with the PMOSs 15 and 21, the saturation drain currents of the PMOSs 14, 15 and 21 are equal to the current I. Further, the drain current of the NMOS 16 connected in cascade with the PMOS 15 becomes equal to the current I. Since the NMOS 16 constitutes a current mirror circuit together with the NMOS 31, the NMOS 16 and 3
The saturated drain current of 1 is equal to the current I. When the charge / discharge switching control signal S34 output from the Schmitt circuit 34 is at "H" level, the NMOS 32 turns on and the NMO
The capacitors 33 are discharged with a constant current I by S32 and S31. When the charge / discharge switching control signal S34 is at "L" level, the PMOS 22 is turned on and the PMOS 22, 21
Thus, the capacitor 33 is charged with a constant current I.
For example, the threshold V on the “H” level side of the Schmitt circuit 34
Let IH be VH and the threshold VIL on the “L” level side be VL. When the voltage VM at the connection point N is VL> VM, the PMOS
22 is turned on, the NMOS 32 is turned off, the capacitor 33 is charged by the current I, the voltage VM rises, and VM = V
Charging continues until it reaches H. When VM> VH, NMO
S32 turns on, PMOS22 turns off, and capacitor 33
Is discharged by the current I, the voltage VM drops, and VL =
Discharge continues until it reaches VM.

As described above, the voltage VM at the connection point N changes like a sawtooth wave between the threshold values VL and VH of the Schmitt circuit 34, and the waveform is shaped by the inverters 35 and 36.
Repeated pulses are generated as the output voltage V _out . Therefore, the oscillation frequency f is f = 1 / T = I / {2C ₃₃ · (VH-VL)} (1) where C is the time when one round trip between the threshold values VH and VL is T ₃₃ : The capacitance value of the capacitor 33. Since I = V _in / R ₁₃ , the frequency f can be adjusted by adjusting the resistance value of the adjusting resistor 13.

[0006]

However, the conventional VCO has the following problems and it is difficult to solve them. In a conventional VCO, I = V _in /
By substituting R ₁₃ into the equation (1), the oscillation frequency f becomes the following equation (2). f = V _in / {2C ₃₃ R ₁₃ · (VH-VL)} (2) From this equation (2), the VCO range is as shown in FIG.
It becomes ± 100% with respect to the center frequency f ₀ . for that reason,
The sensitivity to noise of the input voltage V _in cannot be adjusted, resulting in deterioration of jitter characteristics. The present invention provides a VCO that solves the problem that the prior art has, that the VCO range cannot be adjusted with respect to the input voltage, enables the VCO range to be adjusted, and can also adjust the center frequency. is there.

[0007]

In order to solve the above-mentioned problems, a constant current circuit for outputting a constant current corresponding to an input voltage in response to the input voltage, and a capacitor for charging / discharging are provided. And a waveform shaping circuit for performing waveform shaping by comparing the voltage of the capacitor with a threshold, and a constant current for switching the output of the waveform shaping circuit and charging and discharging the capacitor with a constant current based on the output of the constant current circuit. In a VCO having a charging / discharging circuit, the constant current circuit,
VCO range adjusting means and center frequency adjusting means are provided. In a second invention, the constant current circuit of the first invention is a VCO range connected to the first and second feedback constant current circuits and the output side of the first and second feedback constant current circuits. And resistors for adjustment and frequency adjustment.

[0008]

According to the first aspect of the invention, since the VCO is configured as described above, the VCO range adjusting means and the center frequency adjusting means change the output current of the constant current circuit by adjusting them. When the output current of the constant current circuit changes, the constant current corresponding thereto charges and discharges the capacitor in the constant current charging / discharging circuit, and the oscillation frequency changes so that the VCO range and the center frequency can be adjusted. According to the second invention,
When the resistance values of the VCO range adjusting resistor and the frequency adjusting resistor are changed, the output current of the constant current circuit changes, the capacitor is charged and discharged with a constant current based on the output current, and the oscillation frequency changes. Therefore, the above problem can be solved.

[0009]

1 is a circuit diagram of a VCO showing an embodiment of the present invention. This VCO has a constant current circuit 40 different from the conventional one.
And the same PMOS 51, NMOS 52, constant current charging circuit 60, constant current discharging circuit 70, capacitor 73,
With the Schmitt circuit 74 and the inverters 75 and 76,
It is configured. The constant current circuit 40 includes two first and second
Feedback constant current circuit of the operational amplifier 4
₁ , 42 and N for current control for controlling the currents I ₁ and I _2.
MOS 43 and 44, resistors 45 and 46 for VCO adjustment and frequency adjustment, and resistors 47 and 4 for generating reference voltage V _r
8 and. That is, one operational amplifier 41
The input voltage V _in is input to the negative input terminal, and is feedback-connected to the positive side input terminal via the current control NMOS43 its output terminal. The current control NMOS 43 is
Power supply voltage VC via drain NMOS 49
It is connected to C and the source is connected to GND via the resistor 45. The reference voltage V _r is input to the negative side input terminal of the other operational amplifier 42, and its output terminal is feedback-connected to the positive side input terminal via the current control NMOS 44. In the current control NMOS 44, the drain is connected to the power supply voltage VCC via the load PMOS 49, and the source is connected to the GND via the resistor 46. The resistors 47 and 48 for generating the reference voltage V _r are connected to the power supply voltage V
It is connected in series between CC and GND.

The gate and drain of the PMOS 49 are
The gate of the PMOS 51 is connected, the source of the PMOS 51 is connected to the power supply voltage VCC, and the drain is connected to the GND via the PMOS 52. A constant current charging circuit 60 is connected to the gate and drain of the PMOS 49. Further, the constant current discharge circuit 70 is connected to the gate of the NMOS 52. The constant current charging circuit 60 is a circuit for charging the capacitor 73 connected to the connection point N10 with a constant current, and the gate control is performed by the current I ₃ flowing through the PMOS 49 and the charge / discharge switching output from the Schmitt circuit 74. Control signal S
NMO for switching gated by 74
S62, which have a power supply voltage VCC and a connection point N1.
It is connected in series with 0. Constant current discharge circuit 70
Is a circuit for discharging the capacitor 73 with a constant current,
It has an NMOS 71 whose gate is controlled by the current I ₃ flowing through the NMOS 52, and a switching NMOS 72 whose gate is controlled by the charge / discharge switching control signal S74, which are connected in series between the connection point N10 and GND. . The input terminal of the Schmitt circuit 74 is connected to the connection point N10, and the two-stage waveform shaping inverters 75 and 76 that output the output voltage V _out are connected to the output terminal thereof. The PMOSs 49, 51 and 61 form a current mirror circuit having a mirror coefficient of 1: 1: 1. The NMOSs 52 and 71 form a current mirror circuit having a mirror coefficient of 1: 1.

[0011] Figure 2 is a characteristic diagram showing the relationship between the input voltage V _in the VCO of Figure 1 and the oscillation frequency f _0. VINA is the voltage value of the input voltage V _in, f ₀ is the center frequency. The operation of FIG. 1 will be described with reference to FIG. Input voltage V
_{When in} is input to the negative input terminal of the operational amplifier 41, the gate of the NMOS 43 is controlled by the output of the operational amplifier 41, and a constant current I ₁ flows through the resistor 45. The current I _{1 is, I 1 = V in / R} 45 ( where, R _45; resistance value of the resistor 45) becomes. On the other hand, since the reference voltage V _r is also applied to the negative input terminal of the operational amplifier 42, the output of the operational amplifier 42 gates the NMOS 44,
A constant current I ₂ also flows through the resistor 46. This current I _{2
Is, I 2 = V r / R} 46 ( where, R _46; resistance value of the resistor 46) becomes. Therefore, the constant current I ₃ flowing through the load PMOS 49 is I ₃ = I ₁ + I ₂ = V _in / R ₄₅ + V _r
/ R becomes ₄₆ . The PMOS 49 that passes the current I ₃ is a PMO.
Since constitute a current mirror circuit together with S51,61, the saturation current of their PMOS49 51 and 61 is equal to the current I _3. Further, the drain current of the NMOS 52 connected in cascade with the PMOS 51 becomes equal to the current I ₃ . Since the NMOSs 52 and 71 form a current mirror circuit, those NMOSs 52
And the saturated drain current of 71 is equal to the current I ₃ . Charge / discharge switching control signal S74 output from the Schmitt circuit 74
Is "H" level, the NMO in the constant current discharge circuit 70 is
S72 is turned on, and the capacitor 73 is discharged by the current I ₃ through the NMOSs 72 and 71. When charging and discharging switching control signal S74 is "L" level, PMOS 62 of the constant-current charging circuit 60 is turned on, the capacitor 73 through the PMOS62,61 is charged by the current I _3. For example,
As in the conventional case, the threshold value VIH on the “H” level side of the Schmitt circuit 74 is VH, and the threshold value VIL on the “L” level side is VL.
And When the voltage VM of the connection point N10 is VL> VM,
The PMOS 62 is turned on, the NMOS 72 is turned off, the capacitor 73 is charged by the current I ₃ , and charging continues until the voltage VM rises and VM = VH. When VM> VH, the NMOS 72 is turned on, the PMOS 62 is turned off, the capacitor is discharged by the constant current I ₃ , the voltage VM at the connection point N10 drops, and the discharge continues until VL = VM.
Therefore, the voltage VM is equal to the thresholds VL and V of the Schmitt circuit 74.
A sawtooth wave transition occurs between H. The output of the Schmitt circuit 74 is waveform-shaped by the inverters 75 and 76,
Repeated pulses are output as the output voltage V _out . Thus, the constant current I ₃ flowing through the load PMOS 49 is
Is determined, the current I of the constant current charging circuit 60 and the constant current discharging circuit 70 is determined as in the conventional case. Therefore, V
The oscillation frequency of CO is given by the following equation (3), where T is the time for one round trip between the thresholds VH and VL of the Schmitt circuit 74. _{f = I 3 / {2C 73} (VH-VL)} ··· (3) where, C _73; the input voltage of the capacitance values Figure 2 of the capacitor 73 - as shown in the frequency characteristic, the current flowing through resistor 46 I ₂ Is constant because it does not depend on the input voltage V _in . Since the current I ₁ flowing through the resistor 45 is proportional to the input voltage V _in , there is a constant slope, and this slope has an oscillation frequency f.
Is the same as the slope of the current I ₃ that determines This current I ₃
The larger the slope of, the wider the VCO range, and the smaller the slope, the narrower the VCO range. To increase the VCO range, reduce current I ₂ and increase current I ₁ . V
To narrow the CO range, increase the current I ₂ and increase the current I _2.
Reduce by ₁ . The center frequency f ₀ is set by I ₃ = I ₁
Adjust + I ₂ to the required frequency. As described above, in this embodiment, since the resistors 45 and 46 for adjusting the VCO range and the frequency are provided, the resistors 45 and 46 are provided.
Adjust the oscillation frequency f of the VCO by
The O range can also be adjusted. When the VCO range becomes adjustable, the sensitivity to input noise can be adjusted and the deterioration of jitter characteristics can be prevented.

The present invention is not limited to the above embodiment,
Various modifications are possible. The following are examples of such modifications. (I) The constant current circuit 40 is composed of the first and second feedback constant current circuits and the like, but can be composed of other circuits. (Ii) Schmitt circuit 74 and inverters 75 and 76
May be configured by a waveform shaping circuit having another configuration. For example, two Schmitt circuits may be connected to the connection point N10, and set / reset flip-flops may be provided on the output side of the Schmitt circuits to output a square wave pulse. (iii) Although the VCO in FIG. 1 is composed of MOS transistors, it may be composed of other transistors such as bipolar transistors.

[0013]

As described in detail above, according to the first invention, since the conventional constant current circuit is provided with the VCO range adjusting means and the center frequency adjusting means, the oscillation frequency of the VCO is adjusted and You can also adjust the VCO range. VC
When the O range can be adjusted, the sensitivity to input noise can be adjusted and the deterioration of jitter characteristics can be prevented. According to the second invention, the constant current circuit includes the first and second feedback constant current circuits and resistors for VCO range adjustment and frequency adjustment. Therefore, the value of the resistor should be adjusted. Thus, the oscillation frequency and VCO range can be easily adjusted. Moreover, the circuit configuration of the constant current circuit is simplified.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a VCO showing an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between an input voltage of the VCO of FIG. 1 and an oscillation frequency.

FIG. 3 is a circuit diagram of a conventional VCO.

FIG. 4 is a diagram showing a relationship between an input voltage of the VCO of FIG. 3 and an oscillation frequency.

[Explanation of symbols]

40 constant current circuit 41,42 operational amplifier 43,44 current control NMOS 45,46 resistor for VCO range adjustment and frequency adjustment 49 load PMOS 60 constant current charging circuit 70 constant current discharging circuit 73 capacitor 74 Schmitt circuit 75, 76 Inverter V _in input voltage V _out output voltage

Claims (2)

[Claims] 1. A constant current circuit which outputs a constant current corresponding to an input voltage in response to an input voltage, a charging / discharging capacitor, and a waveform shaping which compares the voltage of the capacitor with a threshold value to perform waveform shaping. In a voltage controlled oscillator comprising a circuit and a constant current charging / discharging circuit for switching the output of the waveform shaping circuit and charging / discharging the capacitor with a constant current based on the output of the constant current circuit, in the constant current circuit, A voltage controlled oscillator, comprising: a voltage controlled oscillator range adjusting means and a center frequency adjusting means. 2. The constant current circuit includes first and second feedback type constant current circuits, and a voltage controlled oscillator range adjusting device connected to the output side of the first and second feedback type constant current circuits. The voltage controlled oscillator according to claim 1, further comprising: a resistor for frequency adjustment.