U.S. patent application number 16/013558 was filed with the patent office on 2018-12-27 for hall sensor readout circuit, corresponding device and method.
This patent application is currently assigned to STMicroelectronics S.r.l.. The applicant listed for this patent is STMicroelectronics S.r.l.. Invention is credited to Paolo ANGELINI, Roberto Pio BAORDA, Danilo Karim KADDOURI.
Application Number | 20180372809 16/013558 |
Document ID | / |
Family ID | 60138886 |
Filed Date | 2018-12-27 |
United States Patent
Application |
20180372809 |
Kind Code |
A1 |
ANGELINI; Paolo ; et
al. |
December 27, 2018 |
HALL SENSOR READOUT CIRCUIT, CORRESPONDING DEVICE AND METHOD
Abstract
Hall sensing signals are received in a spinning readout pattern
of subsequent readout phases, wherein the pattern is cyclically
repeated at a spinning frequency and a polarity of the Hall sensor
signals is reversed in two non-adjacent readout phases of the
readout pattern. A signal storage circuit includes signal storage
capacitors. An accumulation circuit includes accumulation
capacitors. A switch network is selectively actuated to couple the
signal storage capacitors with the accumulation capacitors
synchronously with phases in the spinning readout pattern in
subsequent alternating first and second periods. The spinning
output is stored with alternating opposite signs on the signal
storage capacitors and the Hall sensing signals are stored in the
signal storage capacitors and then accumulated on the accumulation
capacitors with alternate signs in subsequent periods. The
accumulated output signal is then demodulated with a demodulation
frequency half the spinning frequency.
Inventors: |
ANGELINI; Paolo; (Bologna,
IT) ; BAORDA; Roberto Pio; (Milano, IT) ;
KADDOURI; Danilo Karim; (Pero (MI), IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
STMicroelectronics S.r.l. |
Agrate Brianza (MB) |
|
IT |
|
|
Assignee: |
STMicroelectronics S.r.l.
Agrate Brianza (MB)
IT
|
Family ID: |
60138886 |
Appl. No.: |
16/013558 |
Filed: |
June 20, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01R 33/075 20130101;
G01R 33/07 20130101; G01R 33/0017 20130101; G01R 15/202
20130101 |
International
Class: |
G01R 33/00 20060101
G01R033/00; G01R 33/07 20060101 G01R033/07 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 26, 2017 |
IT |
102017000071213 |
Claims
1. A circuit, comprising: a spinning circuit configured to receive
Hall sensor signals in a spinning readout pattern of subsequent
readout phases, the pattern cyclically repeated at a spinning
frequency, wherein the spinning circuit is configured for reversing
the polarity of the Hall sensor signals in two non-adjacent readout
phases in the readout pattern; a signal storage circuit including a
first and a second set of signal storage capacitors; an
accumulation circuit including a set of accumulation capacitors; a
network of switches selectively actuatable to couple the first and
second set of signal storage capacitors in the signal storage
circuit with the output from the spinning circuit and with the set
of accumulation capacitors in the accumulation circuit, wherein
switches of the network of switches are actuatable synchronously
with the readout phases in the spinning readout pattern in
subsequent alternating first and second periods, with the output
from the spinning circuit stored with alternating opposite signs in
the first and second set of signal storage capacitors and the Hall
sensing signal stored in the first and second set of signal storage
capacitors accumulated on the accumulation capacitors with
alternate signs in subsequent periods; and a demodulator circuit
configured to demodulate a signal output from the accumulation
circuit with a demodulation frequency that is half the spinning
frequency.
2. The circuit of claim 1, wherein the set of accumulation
capacitors in the accumulation circuit are resettable at each
period in said subsequent alternating first and second periods.
3. The circuit of claim 1, wherein the set of accumulation
capacitors in the accumulation circuit are resettable at intervals
of four accumulation phases of the signal from the spinning circuit
stored in the first and second set of signal storage
capacitors.
4. The circuit of claim 1, wherein the demodulator circuit includes
a sample and hold circuit that is actuated to sample the signal
output from the accumulation circuit with alternate positive and
negative signs and with a sampling frequency corresponding to said
spinning frequency.
5. The circuit of claim 1, further including an amplifier circuit
couple between the spinning circuit and the signal storage
circuit.
6. The circuit of claim 1, further including at least one low-pass
filter configured to receive an output from the demodulator circuit
and filter out an accumulation circuit offset.
7. The circuit of claim 6, further including a low-pass filter that
is at least partly integrated in the demodulator circuit.
8. The circuit of claim 1, further comprising a Hall sensor
configured to provide said Hall sensor signals.
9. A method, comprising: receiving Hall sensor signals in a
spinning readout pattern of subsequent readout phases, the pattern
cyclically repeated at a spinning frequency, by reversing the
polarity of the Hall sensor signals in two non-adjacent readout
phases in the readout pattern; storing the Hall sensor signals with
said reversed polarity in a first and a second set of signal
storage capacitors; accumulating the stored Hall sensor signals in
a set of accumulation capacitors by selectively feeding the Hall
sensor signals with said reversed polarity to the first and second
set of signal storage capacitors synchronously with the phases in
the spinning readout pattern in subsequent alternating first and
second periods, and selectively feeding the Hall sensor signals
with reversed polarity stored with alternating opposite signs on
the first and second set of signal storage capacitors accumulated
on the accumulation capacitors with alternate signs in subsequent
periods in the subsequent alternating first and second periods;
demodulating an accumulated signal generated by said accumulating
with a demodulating frequency half said spinning frequency.
10. The method of claim 9, further comprising resetting the
accumulation capacitors at each period in said subsequent
alternating first and second periods.
11. The method of claim 9, further comprising resetting the
accumulation capacitors at intervals of four accumulation phases of
the Hall sensor signal stored in the first and second set of signal
storage capacitors.
Description
PRIORITY CLAIM
[0001] This application claims the priority benefit of Italian
Application for Patent No. 102017000071213, filed on Jun. 26, 2017,
the content of which is hereby incorporated by reference in its
entirety to the maximum extent allowable by law.
TECHNICAL FIELD
[0002] The description relates to readout circuits.
[0003] One or more embodiments may provide a readout circuit for a
Hall sensor element for current sensing applications.
BACKGROUND
[0004] A technique currently referred to as "spinning" is
conventionally used for Hall sensor readout in order to reduce the
effects of Hall sensor offset.
[0005] In a conventional arrangement, a Hall-modulated signal can
be amplified in an amplifier stage to be then demodulated and
low-pass filtered to cancel out Hall sensor offset, amplifier stage
offset and 1/f noise.
[0006] A (very) selective low-pass filter may be employed for that
purpose. Spinning the Hall phases at a (very) high frequency may
also be adopted in order to facilitate ripple reduction. By
resorting to such an approach offset and 1/f noise of the low-pass
filter cannot be filtered adequately.
[0007] The reference by Chen et al., "A novel Hall dynamic offset
cancellation circuit based on four-phase spinning current
technique" presented at the Semiconductor Technology International
Conference (CSTIC), Shanghai, China, 15-16 Mar. 2015 (incorporated
by reference), discloses an arrangement where a Hall-modulated
signal is amplified by a first amplifier stage to be then
demodulated by a circuit which introduces a zero in the transfer
function at F.sub.spin providing ripple cancellation.
[0008] The circuit used to obtain ripple cancellation introduces
1/f noise and offset. Additionally such an arrangement may involve
using a type of sample and hold (S&H) circuit which may not be
practical in various applications.
[0009] There is accordingly a need in the art to provide a solution
addressing the foregoing outlined drawbacks.
SUMMARY
[0010] One or more embodiments provide a circuit adapted to comply
with high-bandwidth (for example 200 kHz) and low-noise
specifications.
[0011] One or more embodiments address issues related to the
possible presence of ripple due to the demodulation of the Hall
signal in those arrangements where the Hall signal is demodulated
to baseband with a view to filtering out offset, with current
spinning performed (for example at a frequency F.sub.spin) in order
to cancel out offset.
[0012] One or more embodiments may facilitate cancelling the ripple
introduced by spinning the Hall current by using a discrete-time
accumulator (SC accumulator) to amplify and modulate the Hall
sensor signal with phase generation and sample and hold processing
used to chop the accumulator in order to reduce offset and 1/f
noise therein.
[0013] One or more embodiments may provide one or more of the
following advantages: [0014] high bandwidth, [0015] low noise,
[0016] high temperature stability, and [0017] high accuracy.
[0018] One or more embodiments may facilitate offset and 1/f noise
cancellation in connection with the Hall sensor and an (amplifier)
stage possibly associated therewith as well as in a ripple
cancellation block by introducing a chopper function at a frequency
F.sub.chop=F.sub.spin/2.
[0019] In one or more embodiments, an accumulator having a gain of
four may be used which facilitates relaxing the requirements for an
associated low-pass filter and amplifier stage.
[0020] One or more embodiments may facilitate cancelling output
ripple as caused by a spinning technique.
[0021] In an embodiment, a circuit comprises: a spinning circuit
configured for receiving signals from a Hall sensor in a spinning
readout pattern of subsequent readout phases, the pattern
cyclically repeated at a spinning frequency, wherein the spinning
circuit is configured for reversing (inverting) the polarity of the
sensor signals in two non-adjacent readout phases in the readout
pattern; a signal storage circuit, including a first and a second
set of signal storage capacitors; an accumulation circuit including
a set of accumulation capacitors; a network of switches selectively
actuatable for coupling the first and second set of signal storage
capacitors in the signal storage circuit with the output from the
spinning circuit and with the accumulation capacitors in the
accumulation circuit, wherein the switches in the network of
switches are actuatable synchronously with the phases in the
spinning readout pattern in subsequent alternating first and second
periods, with the output from the spinning circuit stored with
alternating opposite signs on the first and second set of signal
storage capacitors and the sensing signal stored in the first and
second set of signal storage capacitors accumulated on the
accumulation capacitors with alternate signs in subsequent periods;
and a demodulator circuit active on the signal from the
accumulation circuit with a demodulation frequency half the
spinning frequency.
[0022] In one or more embodiments, the accumulation capacitors in
the accumulation circuit may be resettable at each period in said
subsequent alternating first and second periods.
[0023] In one or more embodiments, the accumulation capacitors in
the accumulation circuit may be resettable at intervals of four
accumulation phases of the signal from the spinning circuit stored
in the first and second set of signal storage capacitors.
[0024] In one or more embodiments, the demodulator circuit may
include a sample and hold circuit, actuatable for sampling the
signal from the accumulation circuit with alternate positive and
negative signs with a sampling frequency corresponding to said
spinning frequency.
[0025] One or more embodiments may include an amplifier stage
between the spinning circuit and the signal storage circuit.
[0026] One or more embodiments may include at least one low-pass
filter active on the output from the demodulator circuit to filter
out the accumulation circuit offset.
[0027] One or more embodiments may include a low-pass filter at
least partly integrated in the demodulator circuit.
[0028] In an embodiment, a device comprises: a Hall sensor
providing Hall sensor signals; and a spinning circuit coupled with
the Hall sensor for receiving therefrom said signals in said
spinning readout pattern of subsequent readout phases.
[0029] In one or more embodiments, a method comprises: receiving
signals from a Hall sensor in a spinning readout pattern of
subsequent readout phases, the pattern cyclically repeated at a
spinning frequency, by reversing the polarity of the sensor signals
in two non-adjacent readout phases in the readout pattern; storing
the sensor signals with said reversed polarity in a first and a
second set of signal storage capacitors and accumulating the sensor
signals stored in a set of accumulation capacitors, by selectively
feeding the sensor signals with said reversed polarity to the first
and second set of signal storage capacitors synchronously with the
phases in the spinning readout pattern in subsequent alternating
first and second periods, and the sensor signals with reversed
polarity stored with alternating opposite signs on the first and
second set of signal storage capacitors accumulated on the
accumulation capacitors with alternate signs in subsequent periods
in the subsequent alternating first and second periods; and
demodulating the accumulated signal with a demodulating frequency
half said spinning frequency.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] One or more embodiments will now be described, by way of
example only, with reference to the annexed figures, wherein:
[0031] FIGS. 1A-1D illustrate in an exemplary manner a "spinning"
readout of a Hall sensor,
[0032] FIG. 2 is a block diagram exemplary of embodiments,
[0033] FIG. 3 includes seven superposed time diagrams, referred to
a common abscissa time scale, exemplary of signals which may be
generated in embodiments, and
[0034] FIG. 4 is another circuit diagram substantially
corresponding to the diagram of FIG. 2 providing further details on
possible operation of embodiments.
DETAILED DESCRIPTION
[0035] In the ensuing description, one or more specific details are
illustrated, aimed at providing an in-depth understanding of
examples of embodiments of this description. The embodiments may be
obtained without one or more of the specific details, or with other
methods, components, materials, etc. In other cases, known
structures, materials, or operations are not illustrated or
described in detail so that certain aspects of embodiments will not
be obscured.
[0036] Reference to "an embodiment" or "one embodiment" in the
framework of the present description is intended to indicate that a
particular configuration, structure, or characteristic described in
relation to the embodiment is comprised in at least one embodiment.
Hence, phrases such as "in an embodiment" or "in one embodiment"
that may be present in one or more points of the present
description do not necessarily refer to one and the same
embodiment. Moreover, particular conformations, structures, or
characteristics may be combined in any adequate way in one or more
embodiments.
[0037] The references used herein are provided merely for
convenience and hence do not define the extent of protection or the
scope of the embodiments.
[0038] A Hall sensor as discussed herein can be regarded as a
distributed resistive Wheatstone bridge provided with a set of
pairs of nodes, for example four nodes or "pads" which can be
designated (in an orderly manner) V1, V2, V3 and V4 based on the
output sensing voltages which can be sensed at such nodes.
[0039] According to principles which are known per se (thus making
it unnecessary to provide a more detailed description herein) a
conventional spinning readout pattern of a four-pad Hall sensor
involves rotating by steps of, for instance, 90.degree., the bias
current(s) Ipol as schematically shown in FIGS. 1A-1D.
[0040] The spinning circuit will correspondingly include a set of
switches which are used to couple the pads of the Hall plate (V1,
V2, V3 and V4) to the bias circuit and to the input of a reading
chain to sense the signals V1, V2, V3 and V4 in four phases which
are repeated cyclically at a frequency F.sub.spin, and where the
connections of the pads as used for sensing are correspondingly
similarly "rotated" or "spun" (for example clockwise): [0041] Phase
1: the bias current flows from V1 to V3 (that is, "down" as shown
in FIG. 1A); positive output connected to V2, negative output
connected to V4; [0042] Phase 2: the bias current flows from V2 to
V4 (that is, "to the left" as shown in FIG. 1B); positive output
connected to V3, negative output connected to V1; [0043] Phase 3:
the bias current flows from V3 to V1 (that is, "up" as shown in
FIG. 1C); positive output connected to V4, negative output
connected to V2; [0044] Phase 4: the bias current flowing from V4
to V2 (that is, "to the right" as shown in FIG. 1D); positive
output connected to V1, negative output connected to V3.
[0045] Such a spinning readout pattern of a Hall sensor may be
regarded as involving a readout cycle (repeated at a frequency
F.sub.spin) of an ordered sequence of pads, for example V1, V2, V3,
V4 which are arranged in pairs of opposed pads (for example V1-V3
and V2-V4).
[0046] Such a spinning readout pattern will thus include subsequent
adjacent phases wherein a bias current "spins" ("down", "to the
left", "up", "to the right", "down" and so on, that is by angular
steps of, for instance, 90.degree. as exemplified in FIGS. 1A-1D),
that is flows between a first pair of opposed sensor pads and an
output voltage is sensed across a second pair (different from the
first pair) of opposed sensor pads, with the first and second pairs
of pads "rotated" or "spun" (clockwise or counterclockwise), that
is varied stepwise according to the ordered sequence of the pads,
so that at each rotation/spinning step each pad is, so to say,
"replaced" by an adjacent pad in the sequence when spinning
proceeds for one readout phase to an adjacent phase.
[0047] In one or more embodiments as exemplified herein the pads
V1, V2, V3 and V4 from the Hall sensor H (which per se may be
distinct from the embodiments) are connected to a spinning circuit
10 to provide to an amplifier stage (Amp) 12 a sensing signal Vin
obtained according to a spinning readout pattern of the pads V1,
V2, V3 and V4 as discussed in the following.
[0048] Reference 14 denotes a demodulator circuit configured for
operating (as discussed in the following) as a demodulator at
frequency F.sub.spin (equal to the spinning frequency).
[0049] In one or more embodiments as exemplified herein, the
demodulator circuit 14 includes four capacitors C1, C2, C3, C4 set
between the amplifier stage 12 and an accumulator stage 16
including an operational amplifier (opamp 16a).
[0050] The capacitors C1, C2, C3, C4 can be selectively coupled to
the outputs of the amplifier stage 12: a differential layout is
assumed as conventionally used for amplifying the output Vin from a
spinning circuit 10, which--as discussed previously--may be by
itself differential.
[0051] Coupling is via a set of switches such as electronic
switches, for example MOSFET transistors. These switches are
designated F1 and F2 in the figures in compliance with their "on"
(conductive) and "off" (non-conductive) states as discussed in the
following.
[0052] Further switches coupled to the opposed ends of the
capacitors C1, C2, C3, C4 a general "pi" layout permit to
selectively set to ground either one of the opposed ends of the
capacitors C1, C2, C3, C4. These further switches may again be
electronic switches, for example MOSFET transistors and are again
designated F1 and F2 in the figures in compliance with their "on"
(conductive) and "off" (non-conductive) states as discussed in the
following.
[0053] Still further switches permit to couple the capacitors C1,
C2, C3, C4 to the (differential) inputs of an accumulator stage 16
including a (differential) operational amplifier 16a with feedback
capacitors Cf coupled each between one of the (differential)
outputs of the operational amplifier 16a and a homologous
(differential) input of the of the operational amplifier 16a.
[0054] Once again: [0055] coupling of the capacitors C1, C2, C3, C4
to the accumulator stage 16 may be via electronic switches, for
example MOSFET transistors, [0056] these coupling switches are
designated F1 and F2 in the figures in compliance with their "on"
(conductive) and "off" (non-conductive) states as discussed in the
following.
[0057] Two further such switches (for example MOSFET transistors)
designated RST are coupled to the capacitors Cf in the accumulator
stage 16 with the capability of selectively short-circuiting
(resetting) the feedback capacitors Cf coupled to the operational
amplifier 16a.
[0058] As discussed in the following, the various switches F1, F2
and the switches RST can be regarded as operating as a chopper at a
frequency F.sub.chop equal to half the spinning frequency
F.sub.spin (that is, F.sub.chop=F.sub.spin/2).
[0059] The (differential) output Vout_ACC from the accumulator 16
is fed to a demodulator (for example a sample and hold) circuit 18
intended to operate at the chopping frequency F.sub.chop
(F.sub.chop=F.sub.spin/2) followed by a (1st order) low pass filter
20 (here shown as a distinct element, but possibly included in the
demodulator block 18) providing an output signal Vout, possibly
followed by a (2nd order) low-pass filter 22.
[0060] Clocking signals for the various circuits and the switches
(for example F1, F2, RST) as discussed herein can be derived from
(otherwise conventional) clock circuitry not visible in the figures
for simplicity of representation.
[0061] In one or more embodiments as exemplified herein, the
conventional spinning scheme as discussed previously can be
modified (for example in the spinning circuit 10) in the following
way: [0062] Phase RST: the bias current Ipol flows from V1 to V3;
with the output Vin (in FIGS. 2 and 4) taken as a positive output
connected to V2 and negative output connected to V4; [0063] Phase
1: the bias current Ipol flows from V2 to V4; positive output
connected to V1, negative output connected to V3 [0064] Phase 2:
Bias current flowing from V3 to V1; positive output connected to
V4, negative output connected to V2 [0065] Phase 3: Bias current
flowing from V4 to V2; positive output connected to V3, negative
output connected to V1.
[0066] As noted, the sign of the output voltages in Phases 1 and 3
(i.e., subsequent, non-adjacent phases) is here reversed (V1-V3 and
V3-V1, respectively) in comparison the output voltages in Phases 2
and 4 (V3-V1 and V1-V3, respectively) in conventional spinning as
discussed previously.
[0067] As discussed in the following, in one or more embodiments a
further phase (Phase 4) may be envisaged for timing operation of
the accumulator circuit 16, where the connections of the Hall
sensor nodes V1, V2, V3 and V4 essentially amount to a "don't care"
condition, such a phase possibly being (much) shorter than the
others.
[0068] The spinning readout pattern of one or more embodiments as
discussed above can again be regarded as a readout cycle (adapted
to be repeated at a frequency F.sub.spin) of an ordered sequence of
pads, for example V1, V2, V3, V4 which are arranged in pairs of
opposed pads (for example V1-V3 and V2-V4). Such a spinning readout
pattern will again include subsequent phases wherein a bias current
flows between a first pair of opposed sensor pads and an output
voltage is sensed across a second pair (different from the first
pair) of opposed sensor pads, with the first and second pairs of
pads "rotated" or "spun", that is varied stepwise according to the
ordered sequence of the pads, so that each pad is, so to say,
"replaced" by an adjacent pad in the sequence when spinning
proceeds for one readout phase to an adjacent phase.
[0069] In one or more embodiments as exemplified herein the signs
of the output voltages in two phases non-adjacent readout phases
(for example Phases 1 and 3 as exemplified herein) is "reversed",
that is sign-inverted (for example V1-V3 and V3-V1, respectively)
if compared with respect to the output voltages (for example V3-V1
and V1-V3, respectively) in the homologous phases (for example
Phases 2 and 4) in conventional spinning as discussed
previously.
[0070] This reversal can be regarded as a modulation of a useful
Hall sensing signal Vs at a frequency 2*F.sub.spin, where
F.sub.spin is the frequency of a complete spinning cycle.
[0071] For instance, by assuming that the "useful" signal lies
within a certain band F.sub.b<<F.sub.spin, while in
conventional spinning the signal remains in a band+/-F.sub.b around
DC, in the modified "reversed" or "sign inverted" spinning of one
or more embodiments, the signal is moved to a band+/-F.sub.b around
2*F.sub.spin.
[0072] On the other hand, the Hall sensor offset voltage
Offset.sub.Hall (briefly, the Hall offset) associated with the
"useful" component Vs of the signal V.sub.in is modulated at
F.sub.spin since it is different in each one of the four
phases.
[0073] After the amplifier 12 (which may be a conventional
time-continuous voltage amplifier) the useful signal Vs is still
modulated at 2*F.sub.spin, with the offset voltage Offset.sub.Hall
still modulated at F.sub.spin, with an amplifier offset
Offset.sub.A1 (constant at DC) appearing at the output of the
amplifier 12.
[0074] The time diagrams of FIG. 3 are exemplary of a possible
coordinated time behavior (for example with a common abscissa time
scale) of the following signals (from top to bottom): [0075]
control signals V(F1) and V(F2) of the switches F1 and F2: when
V(F1) or V(F2) high=switch "on", namely conductive; when V(F1) or
V(F2) low=switch "off", namely non-conductive; [0076] control
signals RST the switches RST in the accumulator circuit 16: when
RST high=switch "on", namely conductive; when RST low=switch "off",
namely non-conductive; [0077] sampling signal V(SAMPLE) controlling
the demodulator (for example sample & hold) circuit 18; [0078]
output signal Vin from the spinning circuit 10 (modulated at
2F.sub.spin with offset modulated at F.sub.spin); [0079] output
signal Vout_ACC from the accumulator circuit 16; [0080] output
signal Vout from the sample & hold circuit 20.
[0081] In FIG. 3, the timing of the signals VF(1)--and VF(2)--is
also shown compared with the (period 1/F.sub.spin corresponding to
the) frequency F.sub.spin, while the timing of the signals
V(SAMPLE) is shown compared with the (period 1/F.sub.chop
corresponding to the) frequency F.sub.chop=F.sub.spin/2.
[0082] For the sake of clarity of explanation, as shown in FIG. 3,
the period 1/F.sub.spin encompasses 2.5 periods of VF(1) and VF(2)
and the period 1/F.sub.chop encompasses 5 periods of VF(1) and
VF(2). It will be otherwise appreciated that, as noted previously,
in one or more embodiments, Phase 4 may be (even much) shorter than
the others so that 2.5 may de facto correspond to 2, while 5 may de
facto correspond to 4.
[0083] As exemplified in FIG. 3, the switches F1, F2 can be
operated with just two control signals V(F1), V(F2) in order to
implement the following mode of operation arranged over two
alternating periods, namely Period 1 and Period 2.
[0084] Period 1
[0085] Phase RST: RST is high, F1 is high and F2 is low; the
feedback capacitors Cf are reset to zero differential voltage and
in the meantime the input signal is sampled with positive sign on
the input capacitors C1 and C4.
[0086] Phase 1: RST is low, F1 is low and F2 is high; the input
signal stored in C1 and C4 during phase RST is transferred to the
accumulation capacitors Cf connected in a feedback loop in the
accumulator circuit 16; in the meantime, the input signal is
sampled with negative sign on the input capacitors C3 and C2.
[0087] Phase 2: RST is low, F1 is high and F2 is low; the input
signal stored in C3 and C2 during Phase 1 is transferred to the
accumulation capacitors Cf; in the meanwhile, the input signal is
sampled with positive sign on the input capacitors C1 and C4.
[0088] Phase 3: RST is low, F1 is low and F2 is high; the input
signal stored in C1 and C4 during Phase 2 is transferred to the
accumulation capacitors Cf; in the meantime, the input signal is
sampled with negative sign on the input capacitors C3 and C2.
[0089] Phase 4: RST is low, F1 is high and F2 is low; the input
signal stored in C3 and C2 during Phase 3 is transferred to the
accumulation capacitors Cf connected in feedback.
[0090] Period 2
[0091] Phase RST: RST is high, F1 is low and F2 is high; the
feedback capacitors Cf are reset to zero differential voltage and
in the meantime the input signal is sampled with negative sign on
the input capacitors C3 and C2.
[0092] Phase 1: RST is low, F1 is high and F2 is low; the input
signal stored in C3 and C2 during phase RST is transferred to the
accumulation capacitors Cf; in the meantime the input signal is
sampled with positive sign on the input capacitors C1 and C4.
[0093] Phase 2: RST is low, F1 is low and F2 is high; the input
signal stored in C1 and C4 during Phase 1 is transferred to the
accumulation capacitors Cf; in the meantime, the input signal is
sampled with negative sign on the input capacitors C3 and C2.
[0094] Phase 3: RST is low, F1 is high and F2 is low; the input
signal stored in C3 and C2 during Phase 2 is transferred to the
accumulation capacitors Cf; in the meantime, the input signal is
sampled with positive sign on the input capacitors C1 and C4.
[0095] Phase 4: RST is low, F1 is low and F2 is high; the input
signal stored in C1 and C4 during Phase 3 is transferred to the
accumulation capacitors Cf connected in feedback.
[0096] Once again it will be recalled that, in one or more
embodiments, Phase 4 may actually be much shorter than the
others.
[0097] The arrangement just discussed (circuits 14 and 16 in FIGS.
2 and 4) may thus be regarded as including: [0098] a first set of
signal storage capacitors, C1 and C4, [0099] a second set of signal
storage capacitors, C3 and C2, [0100] a set of accumulation
capacitors Cf, and [0101] a network of switches (those designated
F1, F2) selectively activatable under the control of signals V(F1)
and V(F2) for coupling the first (C1, C4) and second set (C3, C2)
of signal storage capacitors in the circuit 14 with the output from
the spinning circuit 10 (via the amplifier 12) and with the
accumulation capacitors Cf in the accumulator circuit 16.
[0102] In an embodiment as exemplified herein, the switches F1, F2
are actuatable synchronously (that is, in a timed relationship)
with the phases RST, Phase 1, Phase2, Phase 3 and Phase 4 in the
spinning readout pattern in two alternating periods, Period 1 and
Period 2.
[0103] In the phases of the two periods, the sensing signal Vin
from the spinning circuit (as received via the amplifier 12) is
thus stored (sampled) with alternating opposite signs on the first
(C1, C4) and second set (C3, C2) of signal storage capacitors (for
example positive on C1, C4 and negative on C3, C2 in the first
period resp. negative on C1, C4 and positive on C3, C2 in the
second period), with the sensing signal stored in the accumulation
capacitors Cf, and the accumulation capacitors Cf reset for example
short circuited via the switches RST in the accumulator block 16)
at each period (for example during the RST phases).
[0104] In operation as discussed previously a signal Vout_ACC is
accumulated at the output of the accumulator circuit 16 with
alternate signs in subsequent periods (for example with positive
sign in "even" periods and negative sign in "odd" periods).
[0105] As a result of operation as discussed previously, the signal
at the input of the accumulator circuit 16 will include: [0106] a
useful signal V.sub.s modulated at F.sub.spin/2, [0107] the Hall
offset signal Offset.sub.Hall including two components, one at
F.sub.spin and one at 3*F.sub.spin, and [0108] the offset from
amplifier 12, namely Offset.sub.A1, at 2*F.sub.spin.
[0109] In the arrangement as exemplified herein, after four
accumulations, in the signal at the output of the accumulator
circuit 16, namely Vout_ACC, V.sub.s will still be at F.sub.spin/2,
while Offset.sub.Hall and Offset.sub.A1 will be cancelled thanks to
the zeroes of the transfer function of the four-level
accumulation.
[0110] On top of V.sub.s there will also be an offset
Offset.sub.accumulator of the operational amplifier(s) in the
accumulator circuit 16, with such an offset Offset.sub.accumulator
being adapted to be regarded as constant at DC: more to the point
this applies to the signal Vout_ACC as re-sampled in the (for
example sample & hold) circuit 18 controlled by the signal
V(SAMPLE) of FIG. 3.
[0111] The demodulator (for example sample and hold circuit)
circuit 18 after the accumulator circuit 16 may include two pairs
of input switches configured for sampling the incoming signal from
the accumulator circuit 16 with alternate positive and negative
signs, with a sampling frequency F.sub.spin, thus acting as
demodulator at F.sub.chop=F.sub.spin/2, that is at half the
spinning frequency F.sub.spin.
[0112] After this demodulation, the useful signal V.sub.s is at DC
(or, to be more precise, in a band+/-F.sub.b around DC), while
V.sub.oAcc is moved at F.sub.spin/2, given that the demodulating
frequency (for example sample and hold sampling frequency) is
F.sub.spin.
[0113] At this point all the offset voltages generated by the Hall
sensor and by the various amplifiers are cancelled, with the
exception of the offset voltage of the operational amplifier(s) in
the accumulator circuit 16: however this is modulated at
F.sub.spin/2 and so can be reduced by low pass continuous time
filters for example 20 and (possibly) 22 that follow the
demodulator (for example sample and hold) circuit 18.
[0114] As indicated, in one or more embodiments a (first order)
low-pass filter can be embedded in the demodulator (sample and
hold) circuit 18.
[0115] Also, it was observed that the offset contribution due the
operational amplifier(s) in the accumulator circuit 16 is small in
comparison with the useful signal: in fact the useful signal has
been already amplified by the gain of the amplifier stage 12,
multiplied by four (that is the intrinsic gain of the accumulator
circuit 16).
[0116] By way of recap, FIG. 4 provides a "frequency-domain"
representation of the arrangement exemplified herein where the
modulation features of the signal components at the output of the
various circuits are summarized for immediate reference.
[0117] Spinning Circuit 10 [0118] Signal (useful): 2F.sub.spin
[0119] Offset.sub.hall: F.sub.spin
[0120] Amplifier Circuit 12 [0121] Signal: 2F.sub.spin [0122]
Offset.sub.Hall: F.sub.spin [0123] Offset.sub.A1: DC
[0124] Demodulator Circuit 14 [0125] Signal: F.sub.spin/2 [0126]
Offset.sub.Hall: F.sub.spin+3F.sub.spin [0127] Offset.sub.A1:
2F.sub.spin
[0128] Accumulator Circuit 16 [0129] Signal: F.sub.spin/2 [0130]
Offset.sub.hall: cancelled [0131] Offset.sub.accumulator: DC [0132]
Offset.sub.A1: cancelled
[0133] Demodulator Circuit 18 [0134] Signal: DC [0135]
Offset.sub.accumulator: F.sub.spin/2
[0136] It will otherwise be recalled that the "useful" signal lies
in fact in a band+/-F.sub.b, so that, for instance, Signal: DC
actually means Signal: +/-F.sub.b around DC.
[0137] In one or more embodiments a circuit may include: [0138] a
spinning circuit (for example 10) configured for receiving signals
(for example four signals V1, V2, V3, V4) from a Hall sensor (for
example H) in a spinning readout pattern of subsequent readout
phases, the pattern cyclically repeated at a spinning frequency
(for example F.sub.spin).
[0139] Such a spinning readout pattern, as applicable to a Hall
sensor having a plurality of pairs of mutually opposed pads (for
instance V1 and V3, V2 and V4 in FIG. 1), includes (in a manner
known to those of skill in the art) subsequent adjacent phases
wherein a bias current "spins" ("down", "to the left", "up", "to
the right", "down" and so on, that is by angular steps of, for
instance, 90.degree. as exemplified in FIG. 1) that is flows
between a first pair of opposed sensor pads (see V1 and V3 in
portion a) of FIG. 1) and an output voltage is sensed across a
second pair (different from the first pair, e.g. V2 and V4) of
opposed sensor pads, with the first and second pairs of pads
"rotated" or "spun" (clockwise or counterclockwise), that is varied
stepwise (e.g., by 90.degree. steps) according to the ordered
sequence of the pads: see, for instance the bias current Ipol
subsequently flowing from V1 to V3 in portion a), from V2 to V4 in
portion b), from V3 to V1 in portion c), and from V4 to V2 in
portion d) of Fguire 1), so that at each rotation/spinning step
each pad is, so to say, "replaced" by an adjacent pad in the
sequence when spinning proceeds for one readout phase to an
adjacent phase.
[0140] In one or more embodiments, the spinning circuit (10) may be
configured for reversing (inverting) the polarity of the sensor
signals for every two subsequent non-adjacent readout phases in the
readout pattern (for example V3-V1 inverted to V1-V3 and V4-V2
inverted to V2-V4 in Phases 1 and 3 after Phase RST, with Phases 1
and 3 being subsequent yet non-adjacent due to the presence of
Phase 2 interleaved therebetween), [0141] a signal storage circuit
(for example 14), including a first (for example C1, C4) and a
second (for example C3, C2) set of signal storage capacitors,
[0142] an accumulation circuit (for example 16) including a set of
accumulation capacitors (for example Cf), [0143] a network of
switches (for example F1, F2) selectively actuatable (for example
via signals V(F1) and V(F2)) for coupling the first and second set
of signal storage capacitors in the signal storage circuit with the
output from the spinning circuit (10, for example through the
amplifier 12) and with the accumulation capacitors in the
accumulation circuit, wherein the switches in the network of
switches are actuatable (configured to be actuated) synchronously
with the phases in the spinning readout pattern in subsequent
alternating first and second periods (see for example the previous
description of Period 1 and Period 2), with the output from the
spinning circuit stored with alternating opposite signs on the
first and second set of signal storage capacitors and the sensing
signal stored in the first and second set of signal storage
capacitors accumulated on the accumulation capacitors with
alternate signs in subsequent periods (see again the previous
description of Period 1 and Period 2), [0144] a demodulator circuit
(for example 18) active on the signal from the accumulation circuit
with a demodulation frequency (for example F.sub.chop=F.sub.spin/2)
half the spinning frequency (for example F.sub.spin).
[0145] In one or more embodiments, the accumulation capacitors in
the accumulation circuit may be resettable (configured to be reset,
for example via the switches RST) at each period in said subsequent
alternating first and second periods.
[0146] In one or more embodiments, the accumulation capacitors in
the accumulation circuit may be resettable at intervals of four
accumulation phases of the signal from the spinning circuit stored
in the first and second set of signal storage capacitors.
[0147] In one or more embodiments, the demodulator circuit may
include a sample and hold circuit, actuatable (configured to be
actuated) for sampling the signal from the accumulation circuit
with alternate positive and negative signs with a sampling
frequency corresponding to said spinning frequency.
[0148] One or more embodiments may include an amplifier stage (for
example 12) between the spinning circuit and the signal storage
circuit.
[0149] One or more embodiments may include at least one low-pass
filter (for example 20, 22) active on the output from the
demodulator circuit to filter out the accumulation circuit offset
(for example Offset.sub.accumulator).
[0150] One or more embodiments may include a low-pass filter at
least partly (for example 20) integrated in the demodulator
circuit.
[0151] A device according to one or more embodiments may include:
[0152] a Hall sensor (for example H) providing Hall sensor signals
(for example four signals V1, V2, V3, V4), [0153] a circuit
according to one or more embodiments, the spinning circuit (for
example 10) in the circuit coupled with the Hall sensor for
receiving therefrom said signals in said spinning readout pattern
of subsequent readout phases.
[0154] In one or more embodiments a method may include: [0155]
receiving signals from a Hall sensor in a spinning readout pattern
of subsequent readout phases, the pattern cyclically repeated at a
spinning frequency, by reversing (inverting) the polarity of the
sensor signals in two non-adjacent readout phases in the readout
pattern, [0156] storing the sensor signals with said reversed
polarity in a first and a second set of signal storage capacitors
and accumulating the sensor signals stored in a set of accumulation
capacitors, by selectively feeding the sensor signals with said
reversed polarity to the first and second set of signal storage
capacitors synchronously with the phases in the spinning readout
pattern in subsequent alternating first and second periods, and the
sensor signals with reversed polarity stored with alternating
opposite signs on the first and second set of signal storage
capacitors accumulated on the accumulation capacitors with
alternate signs in subsequent periods in the subsequent alternating
first and second periods, [0157] demodulating the accumulated
signal with a demodulating frequency half said spinning
frequency.
[0158] One or more embodiments, may thus involve a reversed
polarity of the sensors signals for (every) two subsequent,
non-adjacent readout phases. In contrast to known spinning
techniques, in one or more embodiments the polarity of the sensor
signals may be reversed at every phase as discussed previously, so
that the resulting read-out pattern of the useful signal is plus,
minus, plus, minus.
[0159] In one or more embodiments, the charge accumulated on C1,
C2, C3 and C4 may be completely transferred to the capacitors Cf
thanks to the operational amplifiers (opamp) 16a.
[0160] This may be advantageous over arrangements that do not
contemplate the presence of such an opamp, so that the charge may
not be completely transferred (for instance with charge sharing
only). An arrangement as exemplified herein may thus facial having
a gain in the place of an attenuation of the signal.
[0161] In one or more embodiments, the readout chain, starting from
block 10, may process the signals V1, V2, V3 and V4 using the same
circuits in a time multiplex arrangement, thus overcoming the
limitations of those arrangements providing distinct circuits for
reading purposes.
[0162] As noted, one or more embodiments may include: [0163]
accumulation capacitors (for instance Cf) in the accumulation
circuit block built around the opamp 16a that are resettable at
intervals of (for instance) four accumulation phases of the signal
from the spinning circuit stored in the first and second sets of
signal storage capacitors (for instance C1, C4 and C3, C2,
respectively), and/or [0164] a sample and hold circuit block in the
demodulator circuit block actuatable for sampling the signal from
the accumulation circuit block with alternate positive and negative
signs with a sampling frequency corresponding to the spinning
frequency F spin, that is the frequency at which the bias current
Ipol (and the sensing voltages) "spin" by angular steps (of
90.degree. for instance) in the spinning readout pattern.
[0165] Also, it will be appreciated that one or more embodiments
may involve signals and circuits that are fully differential, a
differential arrangement exhibiting a good immunity to external
noise.
[0166] Without prejudice to the underlying principles, the details
and embodiments may vary, even significantly, with respect to what
has been described by way of example only, without departing from
the extent of protection.
[0167] The extent of protection is defined by the annexed claims.
The claims are an integral part of the technical teaching provided
herein.
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