Phase-shift modulation of a direct antenna-driving VCO

• US 5,966,055 A
• Filed: 02/14/1997
• Issued: 10/12/1999
• Est. Priority Date: 02/14/1997
• Status: Expired due to Term

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Thomson, David J., Knoedl, George Jr.
• Primary Examiner(s): Grimm, Siegfried H.
• Application Number:
  US08/799,164
• Time in Patent Office: 970 Days
• Field of Search: 332/100, 332/101, 332/102, 332/103, 332/104, 332/105, 332/127, 332/128, 332/144, 332/146, 375/271, 375/272, 375/274, 375/279, 375/280, 375/281, 375/283, 375/302, 375/303, 375/305, 375/306, 375/308
• US Class Current: 332/103
• CPC Class Codes: H03C 3/0975 applying frequency modulation in the phase locked loop at components other than the divider, the voltage controlled oscillator or the reference clock

Abstract

Apparatus for generating the family of PSK (phase shift keyed) modulations, which include BPSK (binary PSK), QPSK (quaternary PSK), MSK (minimum shift keying) and the like. The carrier is generated with the desired digital information already phase-modulated onto it by directly introducing a phase shift or delay onto the error path of a phase-locked loop. causing the phase-locked loop to create the phase modulation. The [proposed scheme differs from common practice approaches, which are usually implemented by linear synthesis (an AM technique); rather, it] invention employs direct nonlinear synthesis (an FM technique). The invention [yields good phase precision with arbitrary spectral shaping under the constraint of constant envelope signaling. It] permits the connection of the output of a simple, inexpensive VCO (voltage controlled oscillator) directly to a system'"'"'s antenna without the need for intervening circuit elements such as phase splitters, mixers, and the like which is applicable to [. The resulting minimal implementation will lend itself well to] the power, size and cost constraints of a microminiature radio transmitter as might be required, for example, for the up-link of a wrist-phone style communicator.

Claims

1. A modulated oscillator having a radio-frequency output and a modulation input, the frequency or phase of the radio frequency output being controlled by a signal applied to the modulation input, comprising:

a voltage controlled oscillator having a radio-frequency ouptput and a control input, the frequency of the radio-frequency output being controlled by the voltage applied to the control input,

a detector having first and second inputs and an error output, the error output comprising a voltage related to the frequency or phase difference between the signals present at the first and second inputs;

a referene oscillator having a radio-frequency output coupled to the first input of the detector;

the second input of the detector being coupled to the radio-frequency output of the voltage-controlled oscillator, the coupling of the radio-frequency output of the voltage controlled oscillator to the second input of the detector comprising a feedback path;

the error output of the detector being coupled to the control input of the voltage controlled oscillator, the coupling of the error output of the detector to the control input of the voltage controlled oscillator comprising an error path;

such that the error output of the detector is related to the phase or frequency difference between the signal present at the radio-frequency ouptput of the voltage controlled oscillator and the radio-frequency output of the reference oscillator;

the referene oscillator, voltage controlled oscillator, and detector, and the error path and feedback path comprising a phase-locked loop;

the voltage on the error path and the radio-frequency signal on the feedback path comprising a feedback signal in the phase-locked loop, such that the radio frequency output of the modulated oscillator is controlled by the phase-locked loop through the feedback signal, and

a keyed phase shift network in the feedback path of the phase-locked loop between the radio-frequency output of the voltage-controlled oscillator and the second input of the detector, having at least one switching control input coupled to the modulation input such that a signal at a switching control input of the keyed phase shift network causes a phase shift of a predetermined amount;

the keyed phase shift network comprising;

a capacitor having a first end coupled to the second input of the detector and a second end connected to ground;

a first resistor having a first end and a second end, the second end being coupled to the first end of the capacitor;

a second resistor having a first end coupled to the radio-frequency output of the voltage-controlled oscillator and a second end coupled at a common point to the first end of the first resistor;

switching means for making or breaking a connection in response to a signal present at the switching control input, having a first terminal coupled to the radio-frequency output of the voltage controlled oscillator and a second terminal coupled to the common point of the first and second resistors, such that a signal on the switching control input causes the switching means to change conductive state, shunting the second resistor;

the values of the first and second resistors and the capacitor being chosen such that introducing a signal at the switching control input of the switching means, causing the switching means to shunt the second resistor, introduces a change in phase shift of a predetermined value.

2. The modulated oscillator of claim 1, in which the differential phase shift θ

is determined by θ

=Δ

Ω

=-tan^-1 +tan^-1 where ω

_ref is the frequency of the radio-frequency output of the reference oscillator, R₁ is the value of the first resistor, and R₂ is the value of the second resistor, and C is the value of the capacitor.

3. The modulated oscillator of claim 1 in which the switching means is a field effect transistor.

4. A modulated oscillator having a radio-frequency output and a modulation input, the frequency or phase of the radio frequency output being controlled by a signal applied to the modulation input, comprising:

a voltage controlled oscillator having a radio-frequency output and a control input, the frequency of the radio-frequency output being controlled by the voltage applied to the control input,

a detector having first and second inputs and an error output, the error output comprising a voltage related to the frequency or phase difference between the signals present at the first and second inputs;

a reference oscillator having a radio-frequency output coupled to the first input of the detector;

the second input of the detector being coupled to the radio-frequency output of the voltage-controlled oscillator, the coupling of the radio-frequency output of the voltage controlled oscillator to the second input of the detector comprising a feedback path;

the error output of the detector being coupled to the control input of the voltage controlled oscillator, the coupling of the error output of the detector to the control input of the voltage controlled oscillator comprising an error path;

such that the error output of the detector is related to the phase or frequency difference between the signal present at the radio-frequency output of the voltage controlled oscillator and the radio-frequency output of the reference oscillator;

the referne oscillator, voltage controlled oscillator, and detector, and the error path and feedback path comprising a phase-locked loop;

the voltage on the error path and the radio-frequency signal on the feedback path comprising a feedback signal in the phase-locked loop, such that the radio frequency output of the modulated oscillator is controlled by the phase-locked loop through the feedback signal, and

a keyed phase shift netowrk in the feedback path of the phase-locked loop between the radio-frequency output of the voltage-controlled oscillator and the second input of the detector, having at least one switching control input coupled to the modulation input such that a signal at a switching control input of the keyed phase shift network causes a phase shift of a predetermined amount;

the keyed phase shift network being a differential phase shift keyer havng a plurality of switching control inputs, such that a plural;

ity of phase shifts may be introduced by combinations of signals at the plurality of inputs, in which the keyed phase shift network comprises;

a capacitor having a first end coupled to the second input of the detector and a second end connected to ground;

a first resistor having a first end and a second end, the second end being coupled to the first end of the capacitor;

a plurality of Δ

R networks connected in series, each having a signal path input and a signal path output and a switching control input, the signal path input of the first Δ

R network being coupled to the radio frequency output of the voltage-controlled oscillator, the output of the last Δ

R network being coupled to the first end of the first resistor of the phase shift keyer, the switching control input of each Δ

R network being coupled to one of the plurality of switching control inputs of the phase shift keyer, each Δ

R network comprising;

a shift resistor having a first end coupled to the signal path input of the Δ

R network and a second end coupled to the signal path output of the Δ

R network;

switching means means for making or breaking a connection in response to a signal present at the switching control input, having a first terminal coupled to the first end of the shift resistor and a second terminal coupled to the second end of the shift resistor, such that a signal on the switching control input causes the switching means to change conductive state, shunting the shift resistor;

the values of the shift resistors of the Δ

R networks, the first resistor of the phase shift keyer and the capacitor being chosen such that introducing one or more signals at the switching control inputs of the plurality of Δ

R networks causes the switching means of the plurality of Δ

R networks to shunt their respective shift resistors, thus introducing a plurality of phase shifts of predetermined value.

5. The modulated oscillator of claim 4, in which there are two AR networks, and there are four phase shifts of predetermined value chosen such that introducing two signals into the two switching control inputs results in quadrature keying of the output of the voltage controlled oscillator.

6. The modulated oscillator of claim 4, in which the switching means of the AR networks comprises a field-effect transistor.

7. The modulated oscillator of claim 4, in which the AR networks further comprise an additional resistor in series with the switching means.

8. A modulated oscillator having a radio-frequency output and a modulation input, the frequency or phase of the radio frequency output being controlled by a signal applied to the modulation input, comprising:

a voltage controlled oscillator having a radio-frequency output and a control input, the frequency of the radio-frequency output being controlled by the voltage applied to the control input,

a detector having first and second inputs and an error output, the error output comprising a voltage related to the frequency or phase difference between the signals present at the first and second inputs;

a reference oscillator having a radio-frequency output coupled to the first input of the detector;

the second input of the detector being coupled to the radio-frequency output of the voltage-controlled oscillator, the coupling of the radio-frequency output of the voltage controlled oscillator to the second input of the detector comprising a feedback path;

the error output of the detector being coupled to the control input of the voltage controlled oscillator, the coupling of the error output of the detector to the control input of the voltage controlled oscillator comprising an error path;

such that the error output of the detector is related to the phase or frequency difference between the signal present at the radio-frequency output of the voltage controlled oscillator and the radio-frequency output of the reference oscillator;

the reference oscillator, voltage controlled oscillator, and detector, and the error path and feedback path comprising a phase-locked loop;

the voltage on the error path and the radio-frequency signal on the feedback path comprising a feedback signal in the phase-locked loop, such that the radio frequency output of the modulated oscillator is controlled by the phaselocked loop through the feedback signal, and

a phase shift keyer in the error path between the error output of the detector and the control input of the voltage controlled oscillator, having at least one switching control input coupled to the modulation input such that a signal at a switching control input of the phase-shift keyer injects a perturbation into the error path of the phase locked loop, causing a phase shift of a predetermined amount in the radio-frequency output of the voltage controlled oscillator.

9. The modulated oscillator of claim 8, in which the phase-shift keyer comprises a keyed voltage divider having a switching control input, a reference input coupled to a fixed DC reference voltage and a switched output, such that a signal on the switching control input causes a voltage of at least one fixed value to appear at the switched output, such that a signal at the switching control input causes a perturbation of the error voltage on the error path related to the fixed voltage value, causing a phase shift of a predetermined amount in the radio-frequency output of the voltage controlled oscillator.

10. The modulated oscillator of claim 8, in which the cumulative phase of the modulated radio-frequency output of the voltage controlled oscillator is restricted to a predetermined range.

11. The modulated oscillator of claim 10, in which the cumulative phase of the radio-frequency output of the voltage controlled oscillator is restricted to a range of 2x.

12. The modulated oscillator of claim 8, in which the frequency of the radio frequency output of the reference oscillator is less than the frequency of the radio-frequency output of the voltage controlled oscillator, and the phase-locked loop further comprises divider means for dividing the frequency of a signal, the divider means being in the feedback path between the radio frequency output of the voltage controlled oscillator and the second input of the detector.

13. The modulated oscillator of claim 12, in which the cumulative phase of the modulated radio-frequency output of the voltage controlled oscillator is restricted to a predetermined range.

14. The modulated oscillator of claim 13, in which the cumulative phase of the radio-frequency output of the voltage controlled oscillator is restricted to a range of 2π

.

15. The modulated oscillator of claim 14, in which one is added to the count in the divider when the cumulative phase rolls over from 0 to ##EQU28##

16. The modulated oscillator of claim 14, in which one is subtracted from the count in the divider when the cumulative phase rolls over from to 0.

17. A method of generating an RF carrier which is frequency or phase modulated by a modulating signal, the RF carrier being generated by a phase-locked loop oscillator having an RF output and frequency control means including a feedback path having an error voltage, the method comprising introducing a shift in the phase of the error voltage in the feedback path of the phase-locked loop in response to the modulating signal.

18. The method of claim 17, in which the modulating signal is chosen such that RF output is quadrature phase-shift keyed.

19. The method of claim 17, in which the RF output of the oscillator is connected directly to an antenna.

20. A phase-shift modulator for radio-frequency oscillators of the kind comprising a voltage controlled oscillator having a radio-frequency output and a control input, the frequency of the radio-frequency oiutput being controlled by the voltage applied to the control input, a detector having first and second inputs and an error output, the error output comprising a voltage related to the frequency or phase difference between the signals present at the first and second inputs;

a reference oscillator having a radio-frequency output coupled to the first input of the detector;

the second input of the detector being coupled to the radio-frequency output of the voltage-controlled oscillator, the coupling of the radio-frequency outpt of the voltage controlled oscillator to the second input of the detector comprising a feedback path;

the error outpuit of the detector being coupled to the control input of the voltage controlled oscillator, the coupling of the error output of the detector to the control input of the voltage controlled oscillator comprising an error path;

such that the error output of the detector is related to the phase of frequency difference between the signal present at the radio-frequency output of the voltage controlled oscillator and the radio-frequency output of the reference oscillator;

the reference oscillator, voltage controlled oscillator, and detector, and the error path and feedback path comprising aphase-locked loop;

the voltage on the error path and the radio-frequency signal on the feedback path comprising a feedback signal in the phase-locked loop, such that the radio frequency output of the modulated oscillator is controlled by the phase-locked loop through the feedback signal;

the modulator comrpising phase-shift network means for introducing the modulsting signal as a keyed perturbation of the error voltage in the error path in respnse to the modulating signal.

21. The modulator of claim 20, in which the modulating signal is chosen such that RF output is quadrature phase-shift keyed.

22. A modulated oscillator having a radio-frequency output and a modulation input, the frequency or phase of the radio frequency outptu being controlled by a signal appleied to the modulation inpout, comprising:

a voltage controlled oscillator having a radio-frequency output and a control input, the frequency of the radio-frequency output being controlled by the voltage applied to the control input,

a detector having first and secod inputs and an error output, the error output comprising a voltage related to the frequency or phase difference between the signals present at the first and second inputs;

a referene oscillator having a radio-frequency output coupled to the firs input of the detector;

the frequency of the radio frequency output of the reference oscillator being less than the frequency of the radio-frequency output of the voltage controlled oscillator,

the second input of the detector being coupled to the radio-frequency output of the voltage-controlled oscillator, the coupling of the radio-frequency output of the voltage controlled oscillator to the second input of the detector comprising a feedback path;

divider means for dividing the frequency of a signal, the divider means being in the feedback path betwen the radio-frequency output of the voltage controlled oscillator and the second input of the detecotr,

the error output of the detector being coupled to the control input of the voltage controlled oscillator, the coupling of the error output of the detector to the control input of the voltage controlled oscillator comprising an error path;

such that the error output of the detector is related to the phase or frequency difference betwen the signal present at the radio-frequency outptu of the voltage controlled oscillator and the radio-frequency output of the reference oscillator;

the refrenc eoscillator, voltage controlled oscillator, and detector, and the error path and feedback path comrpissing a phse-locked loop;

the voltage on the error path and the radio-frequency signal on the feedback path comprising a feedback signal in the phase-locked loop, such that the radio frequency output of the modulated oscillator is controlled by the phase-locked loop throgh the feedback signal,

a keyed phase shift network in the feeeback path of the phase-locked loop between the radio-frequency outpout of the voltage-cpntrolled oscillator and the second input of the detector, having at least one switching control input coupled to the modulation input such that a signal at a switching control input of the keyed phase shift network causes a phase shift of a predetermined amount;

the cumulative phase of the modulated radio-frequency output of the voltage controlled oscillator is resitrcited to a predetermined range of 2π

by adding to or subtracting from the count in the divider when the cumul;

ative phase rolls over.

23. The modulated oscillator of claim 22, in which one is added to the count in the divider when the cumulative phase rolls over from 0 to ##EQU29##

24. The modulated oscillator of claim 22, in which one is subtracted from the count in the divider when the cumulative phase rolls over from to 0.