VARIABLE FREQUENCY OSCILLATOR AND COMMUNICATION CIRCUIT WITH IT

• US 20080122546A1
• Filed: 06/29/2007
• Published: 05/29/2008
• Est. Priority Date: 07/04/2006
• Status: Active Grant

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Masuda, Toru, SHIRAMIZU, Nobuhiro
• Granted Patent: US 7,592,877 B2
• Time in Patent Office: Days
• US Class Current: 331/34
• CPC Class Codes: H03K 2005/00208 using differential stages
• CPC Class Codes: H03K 2005/00234 using circuits having two logic levels
• CPC Class Codes: H03K 3/0322 with differential cells
• CPC Class Codes: H03K 3/35613 the input circuit having a differential configuration
• CPC Class Codes: H03K 5/133 using a chain of active delay devices
• CPC Class Codes: H03L 1/00 Stabilisation of generator output against variations of physical values, e.g. power supply
• CPC Class Codes: H03L 7/0891 the up-down pulses controlling source and sink current generators, e.g. a charge pump
• CPC Class Codes: H03L 7/0995 the oscillator comprising a ring oscillator
• CPC Class Codes: H03L 7/18 using a frequency divider or counter in the loop H03L7/20, H03L7/22 take precedence
• CPC Class Codes: H03M 9/00 Parallel/series conversion or vice versa digital stores in which the information is moved stepwise per se G11C19/00

Abstract

In a variable frequency oscillator in a semiconductor device, as the variation of an oscillation frequency caused by the variation of temperature and supply voltage and process variation is large, it is difficult to reduce the conversion ratio of control voltage dependent upon phase noise and the oscillation frequency and therefore, phase noise is large. The variation of the oscillation frequency is suppressed and phase noise is reduced by connecting a voltage-to-current conversion circuit that converts input control voltage to control current of a ring oscillator to the ring oscillator where delay circuits a delay time of which increases and decreases according to the amplitude of input control current are cascade-connected by a plurality of stages in a ring and increasing/decreasing current dependent upon any of temperature, supply voltage and the threshold voltage of a transistor inside the voltage-to-current conversion circuit.

Claims

1. A variable frequency oscillator, comprising:

a power supply terminal for connecting to an external power supply;

a ring oscillator in which delay circuits of a plurality of stages are cascade-connected in a ring and each of the delay circuits of the plurality of stages is connected to the power supply terminal in common and which outputs an oscillation signal of a frequency according to control current; and

a current source for frequency control connected to each of the delay circuits of the plurality of stages in common for supplying the control current to the ring oscillator,

wherein the current source for frequency control includes a first current source and a second current source respectively connected to the ring oscillator via a common terminal,

wherein the first current source generates current for frequency control according to input frequency control voltage,

wherein the second current source generates current for compensation according to environmental variation, and

wherein the current for frequency control and the current for compensation are added to be control current of the ring oscillator.

2. The variable frequency oscillator according to claim 1,

wherein the second current source generates current for compensation dependent upon at least one of ambient temperature and the voltage of the external power supply.

3. The variable frequency oscillator according to claim 1,

wherein the second current source generates current for compensation dependent upon ambient temperature, the voltage of the external power supply and the threshold voltage of a transistor.

4. The variable frequency oscillator according to claim 1,

wherein the second current source generates second reference voltage based upon the output of a reference voltage source circuit for process, voltage and temperature (PVT) environment compensation and offset voltage for process, voltage and temperature environment compensation generated based upon the output of the reference voltage source circuit and converts the second reference voltage to second current,

wherein the first current source generates first current based upon input frequency control voltage and the offset voltage for process, voltage and temperature environment compensation, and

wherein the first current and the second current are added to be the current for frequency control.

5. The variable frequency oscillator according to claim 1,

wherein the second current source includes a reference voltage source circuit, and

wherein the reference voltage source circuit includes a first MOS transistor and a resistor and supplies reference voltage dependent upon the threshold voltage of the first MOS transistor to a reference voltage output terminal.

6. The variable frequency oscillator according to claim 1,

wherein the second current source includes a reference voltage source circuit and a reference voltage conversion circuit, and

wherein the reference voltage conversion circuit includes a second MOS transistor and outputs output voltage according to the reference voltage supplied from the reference voltage source circuit as offset voltage for process, voltage and temperature environment compensation.

7. The variable frequency oscillator according to claim 1,

wherein the second current source includes a reference voltage source circuit, a reference voltage conversion circuit, a first voltage select switch circuit and a second voltage controlled current source circuit, and

wherein the first voltage select switch circuit includes a plurality of MOS transistors which are controlled by an input logic signal and the gate size of which can be varied, multiplies input voltages from the reference voltage source circuit and the reference voltage conversion circuit, and outputs the multiplied input voltages to the second voltage controlled current source circuit.

8. The variable frequency oscillator according to claim 1,

wherein the first current source includes a voltage conversion circuit for frequency control, a second voltage select switch circuit and a second voltage controlled current source circuit,

wherein the second current source generates second reference voltage based upon the output of a reference voltage source circuit for process, voltage and temperature environment compensation and offset voltage for process, voltage and temperature environment compensation generated based upon the output of the reference voltage source circuit and converts the second reference voltage to second current,

wherein the voltage conversion circuit for frequency control of the first current source converts frequency control voltage input from an external device to first reference output voltage based upon the offset voltage, and

wherein the second voltage select switch circuit includes a plurality of MOS transistors which is controlled by an input logic signal and the gate size of which can be varied, multiplies the first reference output voltage, and outputs the multiplied first reference output voltage to the second voltage controlled current source circuit.

9. A variable frequency oscillator, comprising:

a power supply terminal for connecting to an external power supply;

a ring oscillator in which delay circuit of a plurality of stages are cascade-connected in a ring and each of the delay circuits of the plurality of stages is connected to the power supply terminal in common and which outputs an oscillation signal of a frequency according to control current; and

a current source for frequency control connected to each of the delay circuits of the plurality of stages in common for supplying the control current to the ring oscillator,

wherein the current source for frequency control includes a first current source and a second current source respectively connected to the ring oscillator via a common terminal,

wherein the first current source includes a voltage conversion circuit for frequency control and a first voltage controlled current source circuit,

wherein the second current source at least includes a first reference voltage source circuit for process, voltage and temperature environment compensation, a second reference voltage conversion circuit for process, voltage and temperature environment compensation and a second voltage controlled current source circuit, and

wherein current of the first current source and current of the second current source are added and are input to the ring oscillator as the control current.

10. The variable frequency oscillator according to claim 9,

wherein a current source for frequency control of the ring oscillator is provided with first and second voltage controlled current source circuits, first and second voltage selectors controlled by a control signal input from an external device, a reference voltage source circuit for process, voltage and temperature environment compensation, a reference voltage conversion circuit for process, voltage and temperature environment compensation and a voltage conversion circuit for frequency control to which voltage for frequency control input from an external device is input,

wherein a terminal common to the first and second voltage controlled current source circuits and each terminal of the plurality of delay circuits are connected,

wherein a control signal input from the external device is converted to first current control voltage via the second voltage selector and the first current control voltage is converted to first current in the first voltage controlled current source circuit,

wherein each output of the reference voltage source circuit and the reference voltage conversion circuit respectively controlled by the control signal is converted to second current control voltage via the first voltage selector and the second current control voltage is converted to second current in the second voltage controlled current source circuit, and

wherein the first and second currents are added to be current for frequency control of the ring oscillator.

11. The variable frequency oscillator according to claim 10,

wherein the first and second voltage selectors are respectively provided with a switch configured by an MOS transistor and each current control voltage is varied by an internal or external logic signal.

12. The variable frequency oscillator according to claim 9, further comprising:

a reference voltage source circuit for process, voltage and temperature environment compensation that generates one or more reference voltages dependent upon either of temperature or supply voltage;

a reference voltage conversion circuit for process, voltage and temperature environment compensation that increases and decreases voltage according to the input reference voltage;

a voltage conversion circuit for frequency control that increases and decreases input control voltage according to the reference voltage and outputs it;

first and second voltage selectors that gradually switch the ratio of input voltage and output voltage by one or more input logic signals; and

first and second variable current sources that generate control current according to the input voltage,

wherein an output terminal of the reference voltage source circuit is connected to an input terminal of the first voltage selector,

wherein an output terminal of the first voltage selector is connected to an input terminal of the first variable current source,

wherein the output terminal of the reference voltage source circuit is connected to an input terminal of the reference voltage conversion circuit,

wherein an output terminal of the reference voltage conversion circuit is connected to a reference voltage input terminal of the voltage conversion circuit for frequency control,

wherein voltage input to the variable frequency oscillator functions as input control voltage of the voltage conversion circuit for frequency control,

wherein an output terminal of the voltage conversion circuit for frequency control is connected to an input terminal of the second voltage selector,

wherein an output terminal of the voltage selector is connected to an input terminal of the second variable current source,

wherein an output terminal of the first and second variable current sources is shared, and

wherein current acquired by adding respective output currents of the first and second variable current sources is used for the input control current of the ring oscillator.

13. The variable frequency oscillator according to claim 9,

wherein the ring oscillator includes delay circuits of K stages, where K stands for an odd number equivalent to 3 or more,

wherein each delay circuit is provided with a first differential signal input terminal, a second differential signal input terminal, a differential signal output terminal and a current input terminal,

wherein the differential signal output terminal of the delay circuit of the M-th stage is connected to the first differential signal input terminal of the delay circuit of the (M+1)th stage with a positive phase and a negative phase inverted and is connected to the second differential signal input terminal of the delay circuit of the (M+2)th stage without inversion, where M stands for an integer equivalent to K−

2 or less,

wherein the differential signal output terminal of the delay circuit of the (K−

1)th stage is connected to the first differential signal input terminal of the delay circuit of the K-th stage with a positive phase and a negative phase inverted and is connected to the second differential signal input terminal of the delay circuit of a first stage without inversion, and

wherein the differential signal output terminal of the delay circuit of the K-th stage is connected to the first differential signal input terminal of the delay circuit of the first stage with a positive phase and a negative phase inverted and is connected to the second differential signal input terminal of the delay circuit of the second stage without inversion.

14. The variable frequency oscillator according to claim 9,

wherein the ring oscillator includes delay circuits of L stages, where L stands for an even number equivalent to 4 or more,

wherein each delay circuit is provided with a first differential signal input terminal, a second differential signal input terminal, a differential signal output terminal and a current input terminal,

wherein the differential signal output terminal of the delay circuit of an M-th stage is connected to the first differential signal input terminal of the delay circuit of an (M+1)th stage with a positive phase and a negative phase inverted and is connected to the second differential signal input terminal of the delay circuit of an (M+2)th stage without inversion, where M stands for an integer equivalent to K−

2 or less,

wherein the differential signal output terminal of the delay circuit of an (L−

1)th stage is connected to the first differential signal input terminal of the delay circuit of an L-th stage with a positive phase and a negative phase inverted and is connected to the second differential signal input terminal of the delay circuit of a first stage with a positive phase and a negative phase inverted, and

wherein the differential signal output terminal of the delay circuit of the L-th stage is connected to the first differential signal input terminal of the delay circuit of the first stage without inversion and is connected to the second differential signal input terminal of the delay circuit of a second stage with a positive phase and a negative phase inverted.

15. The variable frequency oscillator according to claim 9,

wherein the ring oscillator includes the delay circuits of L stages, where L stands for an even number equivalent to 2 or more,

wherein the delay circuit is provided with a differential signal input terminal, a differential signal output terminal and a current input terminal,

wherein the differential signal output terminal of the delay circuit of an M-th stage is connected to the differential signal input terminal of the delay circuit of an (M+1)th stage with a positive phase and a negative phase inverted, where M stands for an integer equivalent to L−

1 or less, and

wherein the differential signal output terminal of the delay circuit of a K-th stage is connected to a first differential signal input terminal of the delay circuit of a first stage with a positive phase and a negative phase inverted.

16. The variable frequency oscillator according to claim 9,

wherein the ring oscillator includes the delay circuits of L stages, where L stands for an even number equivalent to 2 or more,

wherein the delay circuit is provided with a differential signal input terminal, a differential signal output terminal and a current input terminal,

wherein the differential signal output terminal of the delay circuit of an M-th stage is connected to the differential signal input terminal of the delay circuit of an (M+1)th stage with a positive phase and a negative phase inverted, where M stands for an integer equivalent to L−

1 or less, and

wherein the differential signal output terminal of the delay circuit of an L-th stage is connected to a first differential signal input terminal of the delay circuit of a first stage without inversion.

17. The variable frequency oscillator according to claim 10,

wherein the reference voltage source circuit includes first and second NMOS transistors, first and second PMOS transistors and a resistor,

wherein a source terminal of the first NMOS transistor is connected to a ground terminal,

wherein a gate terminal of the first NMOS transistor, a source terminal of the second NMOS transistor and a first terminal of the resistor are connected and a second terminal of the resistor is connected to an ground terminal,

wherein a drain terminal of the first NMOS transistor, a gate terminal of the second NMOS transistor and a drain terminal of the first PMOS transistor are connected,

wherein a gate terminal of the first PMOS transistor, a gate terminal and a drain terminal of the second PMOS transistor and a drain terminal of the second NMOS transistor are connected and configure a reference voltage output terminal,

wherein a source terminal of the first PMOS transistor and a source terminal of the second PMOS transistor are connected to a power supply terminal, and

wherein voltage dependent upon the threshold voltage of the first NMOS transistor is supplied to the reference voltage output terminal.

18. A communication circuit provided with a phase locked loop (PLL),

wherein the PLL includes a phase frequency detector, a charge pump, a loop filter, a voltage controlled oscillator and a divider,

wherein the voltage controlled oscillator comprises:

a power supply terminal for connecting to an external power supply;

a ring oscillator in which delay circuits of a plurality of stages are cascade-connected in a ring and each of the delay circuits of the plurality of stages is connected to the power supply terminal in common and which outputs an oscillation signal of a frequency according to control current; and

a current source for frequency control connected to each of the delay circuits of the plurality of stages in common for supplying the control current to the ring oscillator,

wherein the current source of frequency control includes a first current source and a second current source respectively connected to the ring oscillator via a common terminal,

wherein the first current source generates current for frequency control according to input frequency control voltage,

wherein the second current source generates current for compensation according to environmental variation, and

wherein the current for frequency control and the current for compensation are added to be control current of the ring oscillator.

19. The communication circuit according to claim 18,

wherein the second current source generates current for compensation dependent upon ambient temperature, the voltage of the external power supply and the threshold voltage of a transistor.

20. The communication circuit according to claim 18, further comprising:

a parallel-to-serial converter that converts a parallel input signal to a serial signal;

a serial signal output circuit;

a serial signal input circuit;

a clock and data recovery (CDR) circuit for regenerating a clock signal synchronized with a received signal;

a serial-to-parallel converter that generates a parallel output signal; and

a serializer/deserializer (SERDES) circuit provided with a PLL oscillation frequency switch circuit.