MAGNETIC SENSOR FOR MEASURING AN EXTERNAL MAGNETIC FIELD ANGLE IN A TWO-DIMENSIONAL PLANE AND METHOD FOR MEASURING SAID ANGLE USING THE MAGNETIC SENSOR
Magnetic sensor for measuring an external magnetic field angle in a two-dimensional plane, including: a first and second sensing unit outputting, respectively, a first signal sin(θ) and a second signal cos(θ); a first multiplying DAC receiving the first signal and a first digital input sin(f*t) and outputting a first modulated output signal; a second multiplying DAC receiving the second signal and a second digital input cos(f*t) and outputting a second modulated output signal; a first RC filter receiving the first modulated output signal and outputting a first filtered signal sin(θ)*sin(f*t+RCd); a second RC filter receiving the second modulated output signal and outputting a second filtered signal sin(θ)*sin(f*t+RCd); an adder adding the first and second filtered signals and outputting a summed signal cos(f*t+RCd+θ); and an angle extracting unit for measuring the phase delay between the summed signal and a synchronization signal and determining the angle from the phase delay.
1 . A magnetic sensor for measuring an angle (θ) of an external magnetic field in a two-dimensional plane, comprising:
a first sensing unit outputting a first signal sin(θ) and a second field sensing unit outputting a second signal cos(θ);
a first multiplying DAC receiving the first signal sin(θ) and a first digital input sin(f*t) and outputting a first modulated output signal sin(θ)*sin(f*t), where f is a frequency and t is time;
a clock generator generating a clock synchronization signal;
a second multiplying DAC receiving the second signal cos(θ) and a second digital input cos(f*t) and outputting a second modulated output signal cos(θ)*cos(f*t);
a first RC filter receiving the first modulated output signal and outputting a first filtered signal sin(θ)*sin(f*t+RCd);
a second RC filter receiving the second modulated output signal and outputting a second filtered signal sin(θ)*sin(f*t+RCd), where RCd is a phase delay caused by the first and second RC filter;
an adder configured for adding the first filtered signal with the second filtered signal and outputting a summed signal cos(f*t+RCd+θ); and
an angle extracting unit configured for measuring the phase delay (RCd) between the summed signal and the clock synchronization signal ( 101 ) using a reference output signal cos(f*t+RCd), and for determining the angle from the phase delay (RCd).
2 . The magnetic sensor according to claim 1 , further comprising a comparator receiving the summed signal and configured for finding rising zero cross of the summed signal.
3 . The magnetic sensor according to claim 2 , wherein the angle extracting unit is a counter configured to start counting when the reference output signal cos(f*t+RCd) crosses zero and to stop counting when the summed signal cos(f*t+RCd+θ) crosses zero, the angle being proportional to the count.
4 . The magnetic sensor according to claim 3 , further comprising:
a reference multiplying DAC receiving an analog reference signal and a normalized reference digital input cos(f*t) and outputting a reference modulated output signal cos(f*t); and
a reference RC filter configured for generating the reference output signal cos(f*t+RCd) from inputted reference modulated output signal.
5 . The magnetic sensor according to claim 4 , wherein the reference output signal is inputted in a reference comparator configured for finding rising zero cross of the reference output signal.
6 . The magnetic sensor according to claim 3 , wherein the counter runs at a clock frequency greater than f.
7 . The magnetic sensor according to claim 6 , wherein f*t larger than the angle.
8 . The magnetic sensor according to claim 1 , wherein the first and second multiplying DAC are a four quadrant multiplying DAC.
9 . The magnetic sensor according to claim 1 , wherein the first and second sensing units comprise a plurality of TMR sensing elements arranged in full-bridge circuit.
10 . A method for determining an rotational angle θ in a two-dimensional space of an external magnetic field, using a magnetic sensor comprising:
a first sensing unit outputting a first signal sin(θ) and a second field sensing unit outputting a second signal cos(θ);
a first multiplying DAC receiving the first signal sin(θ) and a first digital input sin(f*t) and outputting a first modulated output signal sin(θ)*sin(f*t), where f is a frequency and t is time;
a clock generator generating a clock synchronization signal;
a second multiplying DAC receiving the second signal cos(θ) and a second digital input cos(f*t) and outputting a second modulated output signal cos(θ) *cos(f*t);
a first RC filter receiving the first modulated output signal and outputting a first filtered signal sin(θ) *sin(f*t+RCd);
a second RC filter receiving the second modulated output signal and outputting a second filtered signal sin(θ)*sin(f*t+RCd), where RCd is a phase delay caused by the first and second RC filter;
an adder configured for adding the first filtered signal with the second filtered signal and outputting a summed signal cos(f*t+RCd+θ); and
an angle extracting unit configured for measuring the phase delay (RCd) between the summed signal and the clock synchronization signal ( 101 ) using a reference output signal cos(f*t+RCd), and for determining the angle from the phase delay (RCd);
the method comprising:
inputting the first signal of the first sensing unit and the first digital input sin(f*t) to the first multiplying DAC to output the first modulated output signal sin(θ)*sin(f*t);
inputting the second signal of the second sensing unit and the second digital input cos(f*t) to the second multiplying DAC to output the second modulated output signal cos(θ)*cos(f*t);
inputting the first modulated output signal in the first RC filter and the second modulated output signal in the second RC filter to output, respectively, the first filtered signal sin(θ)*sin(f*t+RCd) and the second filtered signal sin(θ)*sin(f*t+RCd);
adding the first filtered signal and the second filtered signal in the adder circuit to output the summed signal cos(f*t+RCd+θ);
measuring the phase delay (RCd) between the summed signal and the clock synchronization signal using a reference output signal cos(f*t+RCd) in the angle extracting unit, and determining the angle from the measured phase delay (RCd).
11 . The method according to claim 10 , further comprising providing a first voltage waveform to the first sensing unit to output the first signal sin(θ) and providing a second voltage waveform to the second sensing unit to output the second signal cos(θ).
12 . The method according to claim 10 ,
wherein the magnetic sensor further comprises a comparator; and
wherein the method further comprises inputting the summed signal in the comparator and finding rising zero cross of the summed signal.
13 . The method according to claim 12 ,
wherein the magnetic sensor further comprises a reference multiplying DAC and a reference RC filter; and
wherein the method further comprises inputting an analog reference signal and a normalized reference digital input cos(f*t) in the reference multiplying DAC to output a reference modulated output signal cos(f*t);
and inputting the reference modulated output signal in the reference RC filter to generate the reference output signal cos(f*t+RCd).
14 . The method according to claim 13 ,
wherein the magnetic sensor further comprises a reference comparator; and
wherein the method further comprises inputting the reference output signal in the reference comparator and finding rising zero cross of the reference output signal.