US 7,072,617 B1 · System and method for suppression of RFI interference

Abstract

A system and method for suppressing RFI receives a differential input signal Vd, and a signal Vcm which varies with the common mode component of Vd. Vcm is phase-shifted and then amplified with a programmable gain G1 to produce an output VA1. A subtractor produces an output Vsub which varies with Vd−VA1. Vsub is amplified with a programmable gain G2 to produce an output VA2. An analog input signal processing circuit receives VA2 at an input which has an associated maximum dynamic range. A processor adjusts G2 such that VA2 covers the maximum dynamic range, adjusts the phase shift and G1 to minimize VA2, and adjusts G2 to increase VA2 such that it again covers the maximum dynamic range. The RFI in Vd is substantially subtracted out, thereby enabling the full dynamic range of the analog input signal processing circuit to be employed in receiving Vd.

Claims21

Dependent claims

A radio frequency interference (RFI) suppression system, comprising:

a first input for receiving a differential input signal Vd;
a second input for receiving a signal Vcm which varies with the common mode component of said differential input signal;
a first amplifier PGA1 having a programmable gain G1 which varies in response to a first control signal and which receives Vcm at an input and produces an output VA1 which varies with Vcm*G1;
a subtractor circuit which receives Vd at a first input and VA1 at a second input and produces an output Vsub which varies with Vd−VA1;
a second amplifier PGA2 having a programmable gain G2 which varies in response to a second control signal and which receives Vsub at an input and produces an output VA2 which varies with Vsub*G2;
and
a processor which receives a signal that varies with VA2 at an input and is arranged to:
provide said second control signal to adjust programmable gain G2 such that VA2 equals a predetermined value;
provide said first control signal to adjust programmable gain G1 to minimize VA2;
and
provide, after VA2 is minimized, said second control signal to adjust programmable gain G2 to increase VA2 such that it equals said predetermined value.

8 more elements

A radio frequency interference (RFI) suppression system, comprising:

a first input for receiving a differential input signal Vd;
a second input for receiving a signal Vcm which varies with the common mode component of said differential input signal;
a programmable phase shifter circuit which receives Vcm at an input, introduces a phase shift Φ1 in response to a first control signal, and produces a version of Vcm phase-shifted by Φ1 at its output;
a comparison circuit which sets an enable flag when Vcm is greater than a predetermined threshold Vth;
a first amplifier PGA1 having a programmable gain G1 which varies in response to a second control signal and which receives said phase-shifted version of Vcm at an input and produces an output VA1 which varies with Vcm*G1;
a subtractor circuit which receives Vd at a first input and VA1 at a second input and produces an output Vsub which varies with Vd−VA1;
a second amplifier PGA2 having a programmable gain G2 which varies in response to a third control signal and which receives Vsub at an input and produces an output VA2 which varies with Vsub*G2;
an analog input signal processing circuit which receives VA2 at an input which has an associated maximum dynamic range;
and
a processor which receives a signal which varies with VA2 at an input and is arranged to:
provide said third control signal to adjust programmable gain G2 such that VA2 covers said maximum dynamic range;
provide, if said enable flag is set, said first control signal to adjust programmable phase shift Φ1 to minimize VA2;
provide, if said enable flag is set, said second control signal to adjust programmable gain G1 to minimize VA2;
and
provide, after VA2 is minimized, said third control signal to adjust programmable gain G2 to increase VA2 such that it covers said maximum dynamic range.

12 more elements

A radio frequency interference (RFI) suppression system, comprising:

a first input for receiving a differential input signal Vd which is approximately given by:
Vd=Vdmt+Vrfid, where Vdmt is the desired differential input signal and Vrfid is the differential component of the RFI present in Vd when said system is subjected to RFI;
and
a second input for receiving a signal Vcm which varies with the common mode component of said differential input signal which is approximately given by:
Vcm=Vrfic, where Vrfic is the common mode component of the RFI present in Vcm;
a programmable phase shifter circuit which receives Vcm at an input, introduces a phase shift Φ1 in response to a first control signal, and produces a version of Vcm phase-shifted by Φ1 at its output;
a comparison circuit which sets an enable flag when Vcm is greater than a predetermined threshold;
a first amplifier PGA1 having a programmable gain G1 which varies in response to a second control signal and which receives said phase-shifted version of Vcm at an input and produces an output VA1 which varies with Vcm*G1;
a subtractor circuit which receives Vd at a first input and VA1 at a second input and produces an output Vsub, said subtractor circuit including an enable input which is coupled to said enable flag, said subtractor circuit arranged such that Vsub=Vd−VA1 when said enable flag is set and Vsub=Vd when said enable flag is not set;
a second amplifier PGA2 having a programmable gain G2 which varies in response to a third control signal and which receives Vsub at an input and produces an output VA2 which varies with Vsub*G2, said system arranged such that VA2 is approximately given by:
VA2=G2(Vdmt+Vda·cos(ωt+Φd)−(G1(Vc·cos(ωt+Φc+Φ1)))
where Vda and Vc are the amplitudes of the differential and common mode components of the RFI present in Vd and Vcm, respectively, ω is the frequency of the RFI signal, and Φd and Φc are the phase differences between Vrfid and Vrfic, respectively, and the RFI signal;
such that the RMS value of signal VA2 for a given Vdmt signal is a minimum when Φc+Φ1=Φd and
G1
=
V
da
V
c
;
an analog-to-digital converter (ADC) which has an associated maximum dynamic range which corresponds to a predetermined RMS voltage and which receives VA2 at its analog input and produces a digital word at its digital output which represents VA2;
and
a digital signal processor (DSP) which receives said digital word and said enable flag at respective inputs and is arranged to:
provide said third control signal to adjust programmable gain G2 to make VA2 equal to said predetermined RMS voltage;
provide, if said enable flag is set, said first control signal to adjust programmable phase shift Φ1 to minimize the RMS voltage of VA2;
provide, if said enable flag is set, said second control signal to adjust programmable gain G1 to minimize the RMS voltage of VA2;
and
provide, after the RMS voltage of VA2 is minimized, said third control signal to adjust programmable gain G2 to make VA2 equal to said predetermined RMS voltage.

25 more elements

A method of suppressing radio frequency interference (RFI), comprising:

receiving a differential input signal Vd;
receiving a signal Vcm which varies with the common mode component of said differential input signal;
comparing Vcm with a predetermined threshold and setting an enable flag when Vcm is greater than said predetermined threshold;
phase-shifting signal Vcm by a programmable phase shift amount Φ1;
amplifying said phase-shifted signal Vcm with a programmable gain G1 to produce an output VA1 which varies with Vcm*G1;
subtracting VA1 from Vd to produce an output Vsub;
amplifying Vsub with a programmable gain G2 to produce an output VA2 which varies with Vsub*G2;
receiving VA2 at an input which has an associated maximum dynamic range;
adjusting programmable gain G2 such that said VA2 covers said maximum dynamic range;
adjusting, if said enable flag is set, programmable phase shift amount Φ1 to minimize VA2;
adjusting, if said enable flag is set, programmable gain G1 to minimize VA2;
and
adjusting, after VA2 is minimized, programmable gain G2 to increase VA2 such that it covers said maximum dynamic range.

10 more elements

Dependencies are inferred from the claim text.

System and method for suppression of RFI interference

Life of this patent

System and method for suppression of RFI interference

Life of this patent

Abstract

Claims21