PHASE DETECTOR AND DIGITAL PHASE-LOCKED LOOP

• US 3,644,835 A
• Filed: 12/21/1970
• Issued: 02/22/1972
• Est. Priority Date: 12/21/1970
• Status: Expired due to Term

• Current Assignee: James E. Thompson
• Original Assignee: James E. Thompson
• Inventors: Thompson, James E.
• Primary Examiner(s): Forrer, Donald D.
• Assistant Examiner(s): Hart, R. E.
• Application Number:
  US05/099,764
• Time in Patent Office: 428 Days
• Field of Search: 328/109,133,140,166,155 307/232,295,214
• US Class Current: 327/3
• CPC Class Codes: H03L 7/085 concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal H03L7/10 takes precedence; circuits for comparing the phase or frequency of two mutually-independent oscillations H03D13/00

Abstract

There is disclosed a phase detector which operates in a current mode to detect the phase difference between an analog input signal and a digital input signal. The phase difference between these two signals is provided as a current generated from combined chopping and gain block circuits. Current-mode operation increases the gain obtainable from prior art voltage-mode phase detectors and enables convenient filter circuit design for integration of the output signals from the phase detector. The current-mode phase detector may be used in combination with a voltage-controlled multivibrator circuit to provide a digital phase-locked loop having a high-loop gain and having improved pull-in and hold-in ranges. The combined chopping and gain block circuits enables IC implementation with a minimum number of external connections.

Claims

1. Apparatus for detecting the phase difference between an analog input signal and a digital input signal comprising:

means for generating a signal having a current which is proportional to the phase difference between said input signals, so as to provide a current-mode phase detector operating in a nonlinear region, wherein said phase difference is the relative phase of said input signals with respect to a phase difference of 90* between said input signals, said signal generating means including a source of potential voltage;

first and second current-generating means, said second currentgenerating means generating a constant current in said first current-generating means generating a current having a constant component and a component whose amplitude is responsive to the voltage amplitude of said analog input signal;

an output circuit having first and second legs, one end of said first leg being connected to one end of said second leg and to said source of potential voltage;

means for delivering current from said first current source to said first leg and from said second current source to said second leg in response to said digital input signal being at a first predetermined value, and for delivering current from said first source to said second leg and from said second source to said first leg in response to said digital input signal being at a second predetermined level, the time-averaged difference in current in said first and second legs being proportional to the phase difference between said input signals.

2. The apparatus as recited in claim 1 wherein said output circuit includes means for subtracting the current in said first leg from that in said second leg.

3. The apparatus as recited in claim 1 wherein said output circuit includes resistive elements of equal value in each of said legs between the ends thereof.

4. The apparatus as recited in claim 1 and further including means having an inverting and a noninverting input circuit for amplifying the difference in voltage between said inverting and noninverting input circuits and for providing the amplified result at the output thereof, said output being connected to said one end of said first and second legs, said inverting input circuit being connected to the other end of said first leg and said noninverting input circuit being connected to said other end of said second leg, whereby the current in said first leg is subtracted from that in said second leg, the difference in current being available at either one of said other ends of said legs, said difference in current being proportional to said phase difference.

5. The apparatus as recited in claim 3 and further including an analog input circuit coupled to said first current source, said input circuit having a first resistive element having a resistance Re whereby the difference in current between said first and second legs is given by the expression (Vp/ pi Re) sin theta , where Vp is the peak voltage of said analog input and theta is the quadrature phase difference between said inputs.

6. The apparatus as recited in claim 5 and further including a filter circuit comprising a second resistive element having a resistance Rz and a capacitive element coupled in series with said second resistive element between a reference potential and one of said other eNds of said legs, said capacitive element having a capacitance C, the voltage between said one of said other ends and said reference potential being (Vp/ pi Re) ( theta R- theta V) (RzCs+1/Cs) where theta R is the phase of said analog input signal, theta v is the phase of said digital input signal and s is the Laplace variable.

7. The apparatus as recited in claim 6 and further including a voltage-controlled multivibrator circuit having its voltage control input coupled to said one other end, said current delivery means being responsive to the amplitude of the digital signal available at the output of said voltage-controlled multivibrator, whereby a digital phase-locked loop is formed.

8. Apparatus for detecting the phase difference between an analog and a digital input signal comprising in combination first and second current sources for generating first and second currents in response to the amplitude of said analog input signal such that a push-pull feed is provided;

a gain block, having first and second current source load circuits, one side of each of said current source load circuits adapted to be coupled to a source of potential voltage, and gain block including means for amplifying the voltage difference between the other sides of said current source load circuits and for coupling said amplified difference to said one side of each current source load circuit, said current source load circuits having resistance between opposite sides thereof; and

signal chopping means for connecting said current sources at one time each to different current source load circuit in response to the amplitude of said digital input signal being at a first predetermined value and for reversing said connection at a second time in response to said digital input signal being at a second predetermined value such that said analog and digital input signals are multiplied, whereby the difference in current flowing in said current source load circuits is proportional to the phase difference between said analog and digital input signals.

9. Apparatus for detecting the phase difference between an analog and a digital input signal comprising in combination first and second current sources for generating first and second currents, the current generated by said first current source having a constant component and a variable component having an amplitude responsive to said analog input signal, the current generated by said second current source being at a constant value;

a gain block, having first and second current source load circuits, one side of each of said current source load circuits adapted to be coupled to a source of potential voltage, said gain block including means for amplifying the voltage difference between the other sides of said current source load circuits and for coupling said amplified difference to said one side of each current source load circuit, said current source load circuits having resistance between opposite sides thereof; and

signal-chopping means for connecting said current sources at one time each to a different current source load circuit in response to the amplitude of said digital input signal being at a first predetermined value and for reversing said connection at a second time in response to said digital input signal being at a second predetermined value such that said analog and digital input signals are multiplied.

10. The apparatus as recited in claim 9 wherein said current source load circuits have matching resistance elements between opposite sides thereof.

11. In combination, a phase detector which generates a current proportional to the phase difference between an analog input signal and a digital input signal;

means for integrating said current over time and for providing a voltage proportional to said integrated current; and

voltage-controlled oscillator means for generating said digital signal having a Frequency proportional to the amplitude of said voltage, whereby a digital phase-locked loop is formed in which said digital signal is phase locked with respect to said analog input signal whenever said current is at a minimum.

12. The combination as recited in claim 11 wherein said phase detector includes an input circuit having a resistive element, said voltage being a function of only the following variables:

the resistance of said resistive element, the resistance of the resistance element in said integrating means, the capacitance of the capacitor in said integrating means, the peak voltage of said analog signal, the Laplace variable, and the phase difference between said analog and digital input signals, whereby said input circuit resistance forms part of the filter characteristic of said integrating means and whereby the other elements in said phase detector do not affect the transfer function of said filter.

13. A hybrid phase-shifting circuit comprising in combination a phase detector which generates a current proportional to the phase difference between an analog input signal and a digital input signal, said phase detector including;

first and second current sources for generating first and second currents in response to the amplitude of said analog input signal;

a gain block having first and second current source load circuits, one side of each of said current source load circuits adapted to be coupled to a source of potential voltage, said gain block including means for amplifying the voltage difference between the other sides of said current source load circuits and for coupling said amplified difference to said one side of each current source load circuit, said current source load circuits having resistance between opposite sides thereof; and

signal-chopping means for connecting said current sources at one time each to a different current source load circuit in response to the amplitude of said digital input signal being at a first predetermined value and for reversing said connection at a second time in response to said digital input signal being at a second predetermined value such that said analog and digital input signals are multiplied;

means for integrating the output current of said phase detector over time and for providing a voltage proportional to said integrated current; and

voltage-controlled oscillator means for generating said digital signal having a frequency proportional to the amplitude of said voltage whereby a digital phase-locked loop is formed in which said digital signal is shifted exactly 90* with respect to said analog input signal whenever the current from said phase detector is at a minimum.