U.S. patent application number 14/587817 was filed with the patent office on 2016-06-30 for periodic bandwidth widening for inductive coupled communications.
The applicant listed for this patent is Texas Instruments Incorporated. Invention is credited to ANOOP BHAT, SUBHASHISH MUKHERJEE, KUMAR ANURAG SHRIVASTAVA.
Application Number | 20160191123 14/587817 |
Document ID | / |
Family ID | 56165534 |
Filed Date | 2016-06-30 |
United States Patent
Application |
20160191123 |
Kind Code |
A1 |
MUKHERJEE; SUBHASHISH ; et
al. |
June 30, 2016 |
PERIODIC BANDWIDTH WIDENING FOR INDUCTIVE COUPLED
COMMUNICATIONS
Abstract
A method of inductive coupled communications includes providing
a first resonant tank (first tank) and a second resonant tank
(second tank) tuned to essentially the same resonant frequency,
each having antenna coils and switches positioned for changing a Q
and a bandwidth of their tank. The antenna coils are separated by a
distance that provides near-field communications. The first tank is
driven to for generating induced oscillations to transmit a
predetermined number of carrier frequency cycles providing data.
After the predetermined number of cycles, a switch is activated for
widening the bandwidth of the first tank. Responsive to the
oscillations in the first tank, the second tank begins induced
oscillations. Upon detecting a bit associated with the induced
oscillations, a switch is activated for widening the bandwidth of
the second tank and a receiver circuit receiving an output of the
second tank is reset.
Inventors: |
MUKHERJEE; SUBHASHISH;
(BANGALORE, IN) ; BHAT; ANOOP; (BANGALORE, IN)
; SHRIVASTAVA; KUMAR ANURAG; (BANGALORE, IN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Texas Instruments Incorporated |
Dallas |
TX |
US |
|
|
Family ID: |
56165534 |
Appl. No.: |
14/587817 |
Filed: |
December 31, 2014 |
Current U.S.
Class: |
375/300 |
Current CPC
Class: |
H04L 27/04 20130101;
H04B 5/0087 20130101; H04B 5/0031 20130101 |
International
Class: |
H04B 5/00 20060101
H04B005/00; H04L 27/04 20060101 H04L027/04 |
Claims
1. A method of resonant inductive coupled communications, the
method comprising: driving a first resonant tank (first tank) for
generating induced oscillations with a modulated carrier signal,
said first tank tuned to a first resonant frequency and including
first antenna coils, so that said first antenna coils transmit a
predetermined number of carrier frequency cycles (predetermined
number of cycles) for providing data that is first transition
coded; said first tank further including: a first capacitor coupled
in parallel to said first antenna coils; a first resistor coupled
in series between said first antenna coils; and a first switch
coupled in series between said first antenna coils; after said
predetermined number of cycles, activating said first switch for
widening a bandwidth and changing a Q factor of said first tank;
responsive to said oscillations in said first tank, beginning
induced oscillations in a second resonant tank (second tank), said
second tank tuned to a second resonant frequency that is
essentially equal said first resonant frequency and including: a
second antenna coil that is separated from said first antenna coils
by a distance that provides near-field communications; a second
capacitor coupled in parallel to said second antenna coil; and a
second switch coupled in parallel to said second antenna coil; and
responsive to detecting a bit associated with said induced
oscillations of said second tank, activating said second switch for
widening a bandwidth and changing a Q factor of said second tank,
and resetting a receiver sense circuit coupled to receive an output
of said second tank.
2. The method of claim 1, further comprising: opening said first
switch to bring said first resistor into said first tank; and
opening said second switch to remove a second resistor from said
second tank.
3. The method of claim 1, wherein said modulated carrier signal is
an amplitude-shift keyed (ASK) signal.
4. The method of claim 1, wherein said receiver sense circuit
includes an amplifier: coupled to receive an output of said second
tank at inputs of said amplifier; and coupled in series to a
rectifier and peak detector and a delay block.
5. The method of claim 1, wherein a product of a maximum Q factor
for said first tank and a maximum Q factor for said second tank is
.gtoreq.50.
6. The method of claim 1, wherein said modulated carrier signal is
at a carrier frequency from 500 MHz to 4 GHz.
7. The method of claim 1, wherein said first tank is formed on a
first chip and said second tank is formed on a second chip, and
said first antenna coils and said second antenna coil both comprise
metal loops.
8. The method of claim 7, wherein said first chip and said second
chip are positioned lateral to one another on a split leadframe
within a multi-chip package (MCP), and said first chip and said
second chip both include mold compound thereover and
therebetween.
9. The method of claim 7, wherein said first chip and said second
chip are in a stacked configuration on a substrate within a
multi-chip package (MCP).
10. The method of claim 1, wherein said driving said first tank to
oscillate comprises applying a periodic wave tuned to said first
resonant frequency modulated by said data.
11. A resonant inductive coupled communications system, comprising:
a first resonant tank (first tank) tuned to a first resonant
frequency and including: first antenna coils; a first capacitor
coupled in parallel to said first antenna coils; a first resistor
coupled in series between said first antenna coils; and a first
switch coupled in series between said first antenna coils; a second
resonant tank (second tank) tuned to a second resonant frequency
that is essentially equal said first resonant frequency and
including: a second antenna coil that is separated from said first
antenna coils by a distance that provides near-field
communications; a second capacitor coupled in parallel to said
second antenna coil, and a second switch coupled in parallel to
said second antenna coil; receiver sense circuitry coupled to an
output of said second tank; said first tank arranged to generate
induced oscillations when driven by a modulated carrier signal, so
that said first antenna coils transmit a predetermined number of
carrier frequency cycles (predetermined number of cycles) for
providing data that is first transition coded; a transmit
controller for activating said first switch for widening a
bandwidth and changing a Q factor of said first tank after said
predetermined number of cycles; said second tank arranged to begin
induced oscillations responsive to said oscillations in said first
tank; and said receiver sense circuitry arranged to activate said
second switch for widening a bandwidth and changing a Q factor of
said second tank and to reset itself, responsive to detecting a bit
associated with said induced oscillations of said second tank.
12. The system of claim 11, wherein: opening said first switch is
for bringing said first resistor into said first tank; and opening
said second switch is for removing a second resistor from said
second tank.
13. The system of claim 11, wherein said first tank is formed on a
first chip and said second tank is formed on a second chip, and
said first antenna coils and said second antenna coil comprise
metal loops.
14. The system of claim 13, wherein said first chip and said second
chip are positioned lateral to one another on a split leadframe
within a multi-chip package (MCP), and said first chip and said
second chip both include mold compound thereover and
therebetween.
15. The system of claim 11, wherein said modulated carrier signal
is an amplitude-shift keyed (ASK) signal.
16. The system of claim 11, wherein said receiver sense circuitry
includes an amplifier: coupled to receive an output of said second
tank at inputs of said amplifier; and coupled in series to a
rectifier and peak detector and a delay block.
17. The system of claim 11, wherein a product of a maximum Q factor
for said first tank and a maximum Q factor for said second tank is
.gtoreq.50.
18. The system of claim 11, wherein said modulated carrier signal
is at a carrier frequency from 500 MHz to 4 GHz.
19. The system of claim 13, wherein said first chip and said second
chip are in a stacked configuration on a substrate within a
multi-chip package (MCP).
20. The system of claim 11, wherein said driving said first tank to
oscillate comprises applying a periodic wave tuned to said first
resonant frequency modulated by said data.
Description
CROSS-REFERENCE TO COPENDING APPLICATIONS
[0001] This application has subject matter related to copending
application Ser. No. 14/289,895 entitled "METHOD AND APPARATUS FOR
DIE-TO-DIE COMMUNICATION" that was filed on May 29, 2014.
FIELD
[0002] Disclosed embodiments relate to resonant inductive coupled
communication systems.
BACKGROUND
[0003] Resonant inductive coupling (or electromagnetic induction)
is the near-field wireless transmission of energy between two
inductors (coils) between resonant circuits tuned to resonate at
about the same frequency. The respective coils may exist as a
single piece of equipment or comprise two separate pieces of
equipment.
[0004] The general principle of energy transfer and efficiency for
resonant inductive coupling is that if a given oscillating amount
of energy (for example a pulse or a series of pulses) is forced
into a primary (transmitting) coil which is capacitively loaded,
the coil will "ring", so that oscillating fields will occur, with
the field energy transferring back and forth between the magnetic
field in the inductor and the electric field across the capacitor
at the resonant frequency. This oscillation will decrease (damp)
over time at a rate determined by the gain-bandwidth (Q factor) of
the resonant circuit, mainly due to resistive and radiative losses.
However, provided the secondary (receiving) coil cuts enough of the
magnetic field that it absorbs more energy than is lost in each
cycle of the primary (transmitting) coil, then most of the
transmitted energy can still be transferred.
[0005] The primary coil is generally the L part of a series RLC
resonant circuit (resonant "tank"), and the Q factor for such a
resonant tank is given by:
Q = 1 R L C ##EQU00001##
For example for R=20 ohm, C=1 .mu.F and L=10 mH, Q=5. Because the Q
factor for the resonant tank can be very high, only a small
percentage of the magnetic field needs to be coupled from one coil
to the other coil to achieve a reasonably high energy transfer
efficiency, even though the magnetic field decays quickly with
increasing distance from a coil, the primary coil and secondary
coil can be several diameters apart. It can be shown that a figure
of merit for the energy transfer efficiency (U) from primary coil
and secondary coil is the following:
U=k {square root over (Q.sub.1Q.sub.2)}
[0006] Where k is the coupling coefficient, and Q1 and Q2 are the
Q's for the primary (transmitting) tank and secondary (receiving)
tank. Although assuming a reasonable k-value (k<1) the energy
transfer efficiency for the resonant inductive coupled
communication system can be high, the data rate may be limited
because for a communication channel the maximum data-rate that can
be achieved is limited by the channel's bandwidth, which is given
by the Q of the tank (higher Q means a lower bandwidth). For
example, for a tank tuned at 1 GHz with a Q of 10, the bandwidth is
only 100 MHz. For example, for a binary modulation scheme (e.g.,
ON-OFF keying), the maximum data-rate is 2.times. the available
bandwidth, governed by the well-known Nyquist theorem.
SUMMARY
[0007] This Summary briefly indicates the nature and substance of
this Disclosure. It is submitted with the understanding that it
will not be used to interpret or limit the scope or meaning of the
claims.
[0008] Disclosed embodiments recognize the above-described data
rate limitation for resonant inductive coupled communication
systems is particularly problematic when high speed data transfer
is needed. For example, it may be desirable to achieve a 400+ Mb/s
data rate between semiconductor (e.g., silicon) die having
respective resonant tanks with on-chip antenna coils, where in one
example the tank bandwidth is <1/2 the desired data rate, such
as about 130 MHz in one particular embodiment. This makes the
desired minimum communication data rate of 400 Mb/s for binary
communications not possible as this data rate is >2.times.
bandwidth, which violates the Nyquist theorem.
[0009] Disclosed embodiments include methods of inductive coupled
communications includes providing a first resonant tank (first
tank) and a second resonant tank (second tank) tuned to essentially
the same resonant frequency, each having antenna coils and switches
positioned for changing a Q and a bandwidth of their tank. By
adaptively changing the Q of the transmitter and receiver tanks the
above-described data rate problem is solved. The antenna coils are
separated by a distance that provides near-field communications.
The first tank is driven to oscillate to transmit a predetermined
number of carrier frequency cycles providing data. After the
predetermined number of cycles, a switch is activated for widening
the bandwidth of the first tank. Responsive to the oscillations in
the first tank, the second tank begins induced oscillations. Upon
detecting a bit associated with the induced oscillations, a switch
is activated for widening the bandwidth of the second tank and a
receiver circuit receiving an output of the second tank is
reset.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Reference will now be made to the accompanying drawings,
which are not necessarily drawn to scale, wherein:
[0011] FIG. 1 is a flow chart that shows steps in an example method
of resonant inductive coupled communications including periodic
bandwidth widening, according to an example embodiment.
[0012] FIG. 2A is a depiction of a lateral multichip mode (MCM)
package implementing disclosed resonant inductive coupled
communications including periodic bandwidth widening having
respective die shown as Die 1 and Die 2 on a split lead frame of
the MCM to achieve a high isolation voltage between the Dies,
according to an example embodiment.
[0013] FIG. 2B is a depiction of a vertical MCM package
implementing disclosed resonant inductive coupled communications
including periodic bandwidth widening having respective die shown
as Die 2 on Die 1 stacked on a die pad of the lead frame, according
to an example embodiment.
[0014] FIG. 3A depicts an example arrangement for implementing a
forced resonance of a tank, according to an example embodiment, and
FIG. 3B depicts the input modulated carrier drive signal waveform
and the resulting waveform across the antenna coils, according to
an example embodiment.
[0015] FIG. 4 top plot depicts the effect of disclosed de-Qing on a
tank according to an example embodiment vs. an otherwise equivalent
tank without disclosed de-Qing, and the bottom plot depicts last
stage buffer output as a function of time for the disclosed
transmitter tank employing de-Qing.
[0016] FIG. 5A depicts an example resonant inductive coupled
communications system embodiment including two coupled series tanks
according to an example embodiment, and FIG. 5B depicts waveforms
for the NMOS switches SW2, SW1 and transmitter voltage (Vxmtr)
according to an example embodiment.
[0017] FIG. 6A depicts receiver output waveforms across a receiver
tank without disclosed De-Qing and FIG. 6B depicts receiver output
waveforms across an otherwise equivalent receiver tank including
disclosed De-Qing, according to an example embodiment.
[0018] FIG. 7 shows block diagram depictions of another example
receiver sense circuit architecture, according to an example
embodiment.
[0019] FIG. 8 shows results from a transient simulation across the
receiver tank for a 400 Mbps data input (01010100110011000111)
showing the data input at the top and the data output for the
receiver tank on the bottom, according to an example
embodiment.
DETAILED DESCRIPTION
[0020] Example embodiments are described with reference to the
drawings, wherein like reference numerals are used to designate
similar or equivalent elements. Illustrated ordering of acts or
events should not be considered as limiting, as some acts or events
may occur in different order and/or concurrently with other acts or
events. Furthermore, some illustrated acts or events may not be
required to implement a methodology in accordance with this
disclosure.
[0021] Also, the terms "coupled to" or "couples with" (and the
like) as used herein without further qualification are intended to
describe either an indirect or direct electrical connection. Thus,
if a first device "couples" to a second device, that connection can
be through a direct electrical connection where there are only
parasitics in the pathway, or through an indirect electrical
connection via intervening items including other devices and
connections. For indirect coupling, the intervening item generally
does not modify the information of a signal but may adjust its
current level, voltage level, and/or power level.
[0022] Disclosed embodiments provide communication methods for
resonant inductive coupled communication systems, where the
respective tanks each include switches that periodically reset the
system memory and periodically widen the channel bandwidth (e.g.,
by adding resistance) to achieve a high data rate, beyond (above)
the Nyquist data rate. Disclosed embodiments include methods of
resonant inductive coupled communications including providing a
first resonant tank (first tank) tuned to a first resonant
frequency including a first switch, a first capacitor and a first
antenna coil where the first switch is positioned for changing a Q
and a bandwidth of the first tank, and a second resonant tank
(second tank) tuned to a second resonant frequency that is
essentially equal the first resonant frequency including a second
switch, a second capacitor and a second antenna coil wherein the
second switch is positioned for changing a Q and a bandwidth of the
second tank. As used herein, tank resonant frequencies being
"essentially equal" is defined to be within 10% of one another. The
first antenna coil and second antenna coil are separated from one
another by a distance that provides near-field communications
defined herein as distance providing a minimum coupling coefficient
(k) of 0.01 (or more precisely k*(Q1*Q2).sup.1/2>0.1) The
respective resonant tanks can be series resonant tanks or parallel
resonant tanks.
[0023] The first tank is driven to oscillate with a modulated
carrier signal so that the first antenna coil transmits a
predetermined number of carrier frequency cycles (predetermined
number of cycles) providing data that is first transition coded
(i.e., a 0 to 1 transition or a 1 to 0 transition triggers
transmission of carrier pulses). After the predetermined number of
cycles, the first switch is activated for widening the bandwidth of
the first tank referred to herein as de-Q'ing responsive to the
oscillations in the first tank. Through inductive coupling the
second tank begins induced oscillations, wherein upon a receiver
circuit coupled to receive an output of the second tank detecting a
bit associated with the induced oscillations, the second switch is
activated to widen the bandwidth of the second tank (de-Qing) and
the receiver circuit is reset.
[0024] By disclosed embodiments adaptively de-Q'ing the receiver
tank, the received signal strength can be decoupled (independent)
from the speed of the receiver tank. Disclosed switching allows the
maximum available Q of the receiver tank to be used to provide a
high received signal strength, and adaptive de-Q'ing allows the
receiver tank during other time intervals to achieve higher speed
by adaptively increasing its bandwidth.
[0025] FIG. 1 is a flow chart that shows steps in an example method
100 of resonant inductive coupled communications, according to an
example embodiment. Step 101 comprises providing a first resonant
tank (first tank) tuned to first resonant frequency including a
first switch, a first capacitor and a first antenna coil, wherein
the first switch is positioned for changing a Q and a bandwidth of
the first tank, and a second resonant tank (second tank) including
a second switch, a second capacitor and a second antenna coil,
wherein the second switch is positioned for changing a Q and a
bandwidth of the second tank. The second tank is tuned to a second
resonant frequency that is essentially equal to the first resonant
frequency. The first antenna coil and second antenna coil are
separated from one another by a distance that provides near-field
communications, such as from 0.5 mm to 2 mm.
[0026] Step 102 comprises driving the first tank for generating
induced oscillations with a modulated carrier signal so that the
first antenna coil transmits a predetermined number of carrier
frequency cycles (predetermined number of cycles) providing data
that is first transition coded (see e.g., FIG. 8 described below).
Hence for a "0" to "1" transition or a "1" to "0" transition, a
fixed set of carrier frequency cycles are transmitted. In step 103,
after the predetermined number of cycles, the first switch is
activated for widening the bandwidth and lowering the Q (De-Qing)
of the first tank. For example, after the predefined number of
cycles, a series resistor can be switched into the transmitter tank
to widen its bandwidth and De-Q the tank for hastening the clearing
of the tank memory manifested by its ringing (e.g., see resistor R
318 and NMOS 305 SW1 in FIG. 5A described below).
[0027] Step 104 comprises responsive to the oscillations in the
first tank, through inductive coupling, the second tank begins
induced oscillations. The induced oscillations are amplified and
detected by receiver sense circuitry coupled to an output of the
second tank (e.g., see receiver sense circuit 570 shown in FIG. 5A
described below).
[0028] In step 105 upon detecting a bit associated with the induced
oscillations, the second switch is activated to widen the bandwidth
and reduce the Q of the second tank (De-Qing the second tank), and
a receiver circuit coupled to receive an output of the second tank
is reset. For example, when a bit is detected, the receiver can
promptly begin to clear the receiver's channel memory (its ringing)
to hasten getting ready for the next bit, as it is recognized
herein a new bit cannot be received while the second tank is still
ringing. This way, the receiver is not limited its tanks'
bandwidth. Using a receiver switch, a resistor (or capacitor) can
be brought in parallel to the receive tank to reset (De-Q) it
(widening the tank bandwidth) (see NMOS 305 SW1 and R 318 in FIG.
5A described below). The other circuit ringing sources (e.g.,
filters) can be reset using a ground side switch.
[0029] The detection of a bit and subsequent control of the reset
switch in the receiver tank can be accomplished using embedded
hardware (embedded digital circuits and state machine) with a block
level example of a receiver sense circuit 570 shown in FIG. 5A
described below. A complex processor or microcontroller is not
needed because the decision generally needs to be rendered fast as
the loop settling time (time taken for bit detection to reset)
determines the speed of operation (data rate).
[0030] Although as defined above near-field communications is
defined as distance providing a minimum U=k*(Q1*Q2).sup.1/2 of 1,
disclosed designs generally target a minimum U>0.1 for
efficiency and receiver complexity and robustness of the design.
Lower k values (larger coil separation) can be used with a more
sophisticated receiver, which will generally involve more power and
chip area.
[0031] A product of the maximum Q for the first tank and a maximum
Q for the second resonant tank can be .gtoreq.50. The tank Q
achievable for ICs is typically limited to 8 to 15. The Q can be
higher (e.g., up to 35) for special processes with very thick metal
such as copper. A particular value of Q is generally not important
for disclosed embodiments as the de-Q mechanism described herein
enables working with a large variation of Q.
[0032] The modulated carrier signal is generally at a carrier
frequency from 500 MHz to 4 GHz. The carrier frequency is generally
chosen based on considerations including the process capability,
and data rate needed. In one particular design, a frequency of 2
GHz is chosen for a 180 nm semiconductor (e.g., silicon CMOS)
process to achieve a data rate of about 400 Mb/s. One will
generally need to utilize higher frequency for higher data rates.
One can come down in frequency (e.g., to 500 MHz) if the needed
data rate is lower. However, lower frequency oscillators are
generally bulky (large L and/or large C).
[0033] FIG. 2A is a depiction of a lateral MCM package 200
implementing disclosed resonant inductive coupled communications
including periodic bandwidth widening having respective die shown
as Die 1 and Die 2 on a split lead frame 210 having a first die pad
210a and a second die pad 210b to achieve high voltage isolation
(e.g., several thousand volts) between the respective Die,
according to an example embodiment. The bond wires and leads for
split lead frame 210 are not shown in FIG. 2A for simplicity.
Inductive coupled communications are established between Die 1 and
Die 2 with magnetic coupling between on-chip antenna coils 201 and
202 that are within respective resonant tanks with a first tank on
Die 1 and a second tank on Die 2, where the respective tanks are
tuned with capacitors to resonate at essentially the same tank
frequency.
[0034] Although the antenna coils 201 and 202 are shown being on
chip for Die 1 and Die 2, the antenna coils can also be off chip.
The Die 1 to Die 2 breakdown characteristics of MCM 200 is
generally determined by the mold compound (e.g., epoxy mold
material) shown as mold 218 present between the respective Die. The
separation distance between Die 1 and Die 2 is shown as being 0.5
mm to 1 mm as an example, but can be varied to provide different
breakdown voltages. There is generally no common mode transient
immunity (CMTI) issue as loop currents do not form in the antenna
coils 201 and 202 due to common mode transients. Since the magnetic
field is set up only when loop current flow through the antenna
coils 201 and 202, a CMTI event generally does not cause any
issues. Active circuits (e.g., CMOS circuits) can be implemented on
Die 1 and Die 2 along with the antenna coils, such including a
local oscillator and modulator on the transmitter die and a
receiver circuit on the receiver die. Also, other functions, such
as data-converters, high speed input/outputs (I/Os),
microcontrollers, etc. can also be implemented on the same die.
[0035] FIG. 2B is a depiction of a vertical MCM package 250
implementing disclosed resonant inductive coupled communications
including periodic bandwidth widening having respective die shown
as Die 1 and Die 2 stacked on a die pad 260a of a lead frame 260,
according to an example embodiment. The bond wires and leads for
lead frame 260 are again not shown in FIG. 2B for simplicity. A
dielectric layer 257 is shown between Die 1 and Die 2. In one
arrangement Die 2 can be coupled to Die 1 using through-silicon via
(TSV) technology. There can be mold between the Dies in a stacked
face-to-face assembly, or there can be a laminate material between
the respective Die.
[0036] MCM 200 and MCM 250 are not dependent on any specific
process technology. For example, any process can generally be used
that provides a suitable metal stack for forming the loops for the
antenna coils 201 and 202. MCM 200 and MCM 250 can generally be
used for a variety of other die-to-die coupling applications. For
example, the die to die communication can be embedded as an I/O
module in system-on-chips (SOCs) having other functions, such as
data-converters, high speed I/Os, microcontrollers, etc. that as
noted above can also be implemented on the same die.
[0037] FIG. 3A depicts a transmitter arrangement 300 for
implementing forced resonance of a transmitter tank 310, according
to an example embodiment, and FIG. 3B depicts the input modulated
carrier drive signal waveform and the resulting waveform across the
transmitter coils 320 shown having a first coil with an inductance
of L and a second coil with an inductance of L. A transmit (TX)
controller 330 receives in input driving signal shown as DATA_IN,
where the TX controller 330 generates the modulated carrier 312 and
modulated data signal complement 313 shown. The driving signal can
generally be any periodic wave (e.g., sine or square wave) tuned to
the first resonant frequency. A local oscillator (not shown) can
generate the square waves shown in FIG. 3B tuned to the resonant
(natural) frequency of the transmitter tank 310 which provides the
carrier. This carrier is modulated by data added to the carrier by
the TX controller 330 to produce the modulated data signal 312 and
modulated data signal complement 313 shown input via buffers 314a
and 314b across the transmitter tank 310.
[0038] One particular example of signal processing provided by TX
controller 330 and a brief mention of receive processing comprises
the following:
1. The input data shown as DATA_IN is first transition or edge
coded, i.e. generating a few (pre-determined) carrier pulses for
0->1 and 1->0 data edges. That way, when the input is steady
0 or 1 for a relatively long time, the whole system is kept idle,
conserving power. 2. At the data transition edge, an oscillator
(clock) is started running at 2 GHz to send a few pulses shown as
modulated carriers 312 and 313 in FIGS. 3A and 5A. 3. A counter
counts the number of (pre-defined) oscillator pulses and then stops
the transmission and resets the oscillator. 4. At this time the
RESET or DE-Q (using NMOS 305 SW1 305a in FIG. 3A) pulse is
generated, which lasts for half or one oscillator cycle, which
turns OFF NMOS 305 SW1 to de-Q the transmitter tank 310 and rapidly
dissipate the tank's energy. 5. The whole operation can be
controlled can by a finite state machine, which can be implemented
as hardwire since it runs at 2 GHz. 6. The transmitted pulses are
detected by a receiver sense circuit coupled to a receiver tank as
a bit edge described below relative to FIG. 5A. The receiver sense
circuit then decodes this into levels and sends out the decoded
information as DATA_OUT as shown in FIG. 5A.
[0039] In one possible implementation, the transmitter tank 310 is
driven through AC coupling capacitors each shown in FIG. 3A as C1.
The total transmitter coil inductance of 2L shown as separate L's
resonate with the parallel combination of capacitors C1 and C2. C1
and C2 can be on the order of 1 pF. At each clock, the transmitter
coils 320 receives a voltage step shown at the bottom of FIG. 3B
given by:
Vstep=Vin*C1/(C1+C2)
[0040] Where Vin is the difference between the level of the
modulated data signal 312 and modulated data signal complement 313
which is 3.5 V for the waveforms shown in FIG. 3B. A switch shown
as an NMOS 305 SW1 which includes an enable input (gate electrode)
305a having a resistor R 318 that is in parallel to NMOS 305 SW1.
NMOS 305 SW1 has an ON resistance (R.sub.ON)<<R 318. When
NMOS 305 SW1 is not enabled by a suitable gate-to-source voltage
coupled to enable input 305a, R 310 is introduced as a series
resistance in the transmitter tank 310 for de-Qing the transmitter
tank 310. When NMOS 305 SW1 is enabled (turned ON) by a suitable
gate-to-source voltage coupled to enable input 305a, R 318 is
bypassed by NMOS 305 SW1, which is the higher Q state of the
transmitter tank 310 used for normal transmit operation.
[0041] For de-Qing, the NMOS 305 SW1 is opened which brings R 318
into the transmitter tank 310. There are 2 main reasons for
including R 318 in transmitter tank 310. Firstly, R 318 reduces the
Q of the transmitter tank 310 significantly, widening its bandwidth
and quenching the transmitter tank 310. Secondly, R 318 limits the
instantaneous voltage swing across the NMOS 305 SW1, protecting it
from breakdown or reverse conduction (due to negative voltage). The
second feature also limits how high a resistance for R 318 can
generally be used.
[0042] FIG. 3B depicts the input modulated carrier drive signal
waveform shown as din and the resulting waveform across the pair of
antenna coils shown as "tank_swing". The input modulated carrier
drive signal waveform is shown as a square wave having a 1.8 V
amplitude. The modulated data signal 312 and modulated data signal
bar 313 shown in FIG. 3A allows the transmitter tank 310 to have a
tank swing that is 2 times the positive power supply (VDD) or more,
and also swing negative, shown swinging from about 3 V to -3V in
FIG. 3B. For example, the transmitter tank 310 can swing +/-3V when
coupled to a 1.8V power supply and driven by a buffer having 1.8V
transistors. To achieve fast turn-off (referred to herein as a de-Q
or Quench) of the transmitter tank 310 shown in FIG. 3B of about 1
nsec, NMOS 305 SW1 acting as a series switch can be turned OFF
between its inductors L. This series switch arrangement protects
the NMOS 305 SW1 from high magnitude positive and negative
swings.
[0043] The top plot in FIG. 4 depicts the effect of disclosed
de-Qing on a transmitter tank according to an example embodiment
for the transmitter tank 310 in FIG. 3A vs. an otherwise equivalent
transmitter tank without disclosed de-Qing (lacking NMOS 305 SW1
and R 318). Disclosed de-Qing (shown as "with De-Q") is seen to
significantly speed the damping of the oscillations compared to the
waveform without disclosed De-Qing (shown as "without De-Q"). The
bottom plot in FIG. 4 depicts the last stage buffer output as a
function of time for the disclosed transmitter tank employing
de-Qing. The Last stage buffer output drives the transmitter tank,
and is shown that only some pulses are given to the tank with 3
pulses and the NMOS 305 SW1 being ON during this case. The swing of
the transmitter tank is due to these pulses only. As soon as the
pulses are OFF, R 318 is brought in series by turning NMOS 305 SW1
OFF.
[0044] FIG. 5A depicts an example resonant inductive coupled
communications system 500 including an inductively coupled
transmitter tank 510 including transmitter coils 320 controlled by
TX controller 330, and a receiver tank 520 including receiver coils
530, including a receiver sense circuit 570 having an amplifier 571
that has inputs receiving an output of the receiver tank 520
(between VP_Tank and VM_Tank), according to an example embodiment.
Receiver sense circuit 570 is shown including an amplifier 571,
rectifier and peak detector block 572, Schmitt trigger 573, delay
block 574, mono-shot generator 575 and digital block 576, wherein
an output of the digital block 576 provides the DATA_OUT shown. The
reset signal shown coupled to the rectifier and peak detector block
572 and to the gate electrode of the second NMOS 525 SW2 as a Rx
de-Q signal is generated by the mono-shot generator 575. When a bit
is detected, the Schmitt trigger 573 output triggers to `1` and the
same is used by the mono-shot generator 575 as reset signal after a
suitable delay is provided by the delay block 574.
[0045] The transmitter tank 510 uses a combination of series and
parallel capacitors C1, C2 and C3. The series capacitors C1 and C2
(AC coupling capacitors) are used to drive energy into the
transmitter tank 510. The series capacitors C1 and C2 also protect
the driving transistors of the driving buffers 314a and 314b from
the relatively high voltage generated at the transmitter tank
510.
[0046] The transmitter coils 320 is shown split into two equal coil
parts with a NMOS 305 switch (SW1) in between. When NMOS 305 SW1 is
ON, it essentially shorts the coils together and the inductors work
as a single Inductor in a single LC circuit. This way, when ON, the
NMOS 305 switch transistor (SW1) only sees a very small swing
across it. The tips of the coils go through a +/-3V swing, but only
a small fraction of this swing is seen by the center switch
transistor NMOS 305 SW1.
[0047] Without R1 318, when the NMOS 305 SW1 switch turns OFF (for
de-Qing), a large voltage spike would ordinarily appears across
NMOS 305 SW1. This is avoided by keeping a parallel resistor as R1
318 to SW1. Resistor R1 318 restricts the swing across NMOS 305 SW1
by bypassing the current and also dissipating energy to lower the Q
of the transmitter tank 510. This way de-Qing or quenching of the
transmitter coils 320 can be handled by a low voltage rated
transistor and there is still the ability to handle negative coil
swings.
[0048] Receiver tank 520 is shown including a second NMOS 525 SW2
having an enable input (gate electrode) 525a shown receiving a De-Q
input at the gate. Resistors shown as R2 and R3 in receiver tank
520 are switched into the receiver tank 520 to lower the Q of the
tank when the enable input shown as a de-Q input turns on NMOS 525
SW2. The M with a double sided arrow shown in FIG. 5A depicts
magnetic coupling between the transmitter coils 320 and the
receiver coils 530.
[0049] Regarding operation of the receiver tank 520, a parallel
resistance (R2 and R3, e.g., about 25 Ohms each) is shown for
de-Qing. This arrangement is used for 2 main reasons. Firstly, the
swing in the receiver coils 530 is generally small, typically being
less than +/-300 mV. Accordingly, the switch transistor NMOS 525
SW2 (which sees the entire voltage swing when OFF) can withstand
the voltage. Secondly, a switch in series to the coil (like the
primary side) would need to have a low ON resistance and hence be
large in size. As the switch transistor NMOS 525 SW2 is generally a
large area transistor, when being turned ON and OFF it can setup
parasitic oscillations, which can be falsely detected as a signal.
Hence a series switch (NMOS 305 SW1) used in the transmitter tank
510 is not used in the receiver tank 520, and instead NMOS 525 SW2
is used as a parallel switch. In this scheme, the NMOS 525 SW2
switch is OFF for normal operation and turns ON when the receiver
tank 520 needs to be de-Qed. This operation is exactly opposite
relative to the transmitter tank 510.
[0050] Although not shown in FIG. 5A, there is a parasitic
resistance (e.g. 5 to 10 ohms) inherent to the transmitter and
receiver coils that cannot be accessed. The parasitic resistance
results in a decrease in the inherent Q of the tank, which is
generally desirable to maximize in for disclosed embodiments to
provide a Q of the tank of about 10 to 12. The resistances R 528
and R 529 are shown that are switched in and out of the receiver
tank 520 as needed as is R 318 in the transmitter tank 510.
[0051] During operation of the receiver sense circuit 570 when the
receiver circuit 520 receives a 0' bit, the 0' bit does not have
any energy in it. The receiver sense circuit 570 can be reset to
`0` after every detection of `1` so that the Schmitt trigger 573
does not repeatedly trigger. The receiver sense circuit 570 needs
to detect the `1` and reset to `0` within the bit period, i.e. 2 ns
for the case where one is looking to achieve a maximum data rate of
500 mbps so the decision has to be taken in 2 ns and the system has
to be reset after detection in 2 ns. Ideally the receiver tank 520
will develop a peak to peak voltage of 800 mV in 1.5 ns for a 1%
coupling coefficient (k).
[0052] FIG. 5B depicts waveforms applied to NMOS 525 SW2, NMOS 305
SW1, and transmitter voltage (Vxmtr) which is across the
transmitter tank 510. NMOS 305 SW1 and NMOS 525 SW2 are independent
to each other, and independent decisions of switching NMOS 305 SW1
is taken in transmitter and of switching SW2 is taken in receiver.
However because of switching mechanism it appears they are out of
phase, NMOS 305 SW1 in series of it has to be ON during
transmission and NMOS 525 SW2 is in parallel, so it has to OFF
during transmission else it will short the transmitter coils 320.
After a bit is transmitted NMOS 305 SW1 is deactivated after some
delay only bit is detected at receiver and NMOS 525 SW2 is
activated, so it looks like they are out of phase. Accordingly, the
phase difference between them depends upon delay in the system from
transmitter to receiver.
[0053] FIG. 6A depicts receiver output waveforms across a receiver
tank without disclosed De-Qing and FIG. 6B depicts receiver output
waveforms across an otherwise equivalent receiver tank 520 with
disclosed De-Qing, according to an example embodiment. Disclosed
de-Qing is seen to again speed the damping of the oscillations
compared to the waveform without disclosed De-Qing.
[0054] FIG. 7 shows a block diagram depiction of another example
receiver sensor architecture shown as receiver sense circuit 700,
shown coupled to receive the output from a receiver tank 520 shown
in FIG. 5A, according to an example embodiment. For receiver sense
circuit 700 the rectifier and peak detector block 572 shown within
receiver sense circuit 570 shown in FIG. 5A is replaced by a
positive peak detector block 572a and a negative peak detector
block 572b and the Schmitt trigger 573 shown with receiver sense
circuit 570 is replaced by an amplifier 752 having an input
resistor 753 and feedback resistor 754. Although not shown in FIG.
7, the Vout shown is subsequently processed by a digital block to
provide a DATA_OUT signal, such by the digital block 576 shown as
part of receiver sense circuit 570 in FIG. 5A.
Examples
[0055] Disclosed embodiments are further illustrated by the
following specific Examples, which should not be construed as
limiting the scope or content of this Disclosure in any way.
[0056] Regarding example modulation schemes, since a tuned LC
coupled system provides a bandpass channel, a carrier based
modulation scheme can be used. On-off keying (OOK) is the simplest
form of amplitude-shift keying (ASK) modulation that represents
digital data as the presence or absence of a carrier. A 500 Mbp/s
data rate can be targeted with On/Off Keying (OOK). An example
system' bandwidth is 130 MHz; which means a data rate of around 8
ns. A data rate of 8 ns means one cannot send new data for at least
the next 8 ns because the tank retains memory of data sent earlier
for a period 8 ns, restricting the data rate. To achieve data rate
of about 500 Mbps, each bit needs to be transferred within about 2
ns and system memory needs to be cleared.
[0057] A disclosed De-Q technique is employed at the transmitter
and at receiver to accomplish this desired data transfer rate. When
bit `1` needs to be transmitted, 3 square pulses at 2 GHz are
applied at the transmitter tank. When the data is `0`, no signal is
applied at the transmitter tank. FIG. 8 shows results from a
transient simulation across the receiver tank for a 400 Mbps data
input (01010100110011000111) showing the data input at the top and
the data output for the receiver tank on the bottom, according to
an example embodiment. The data rate shown is 400 mbps operating at
room temperature.
[0058] Those skilled in the art to which this disclosure relates
will appreciate that many other embodiments and variations of
embodiments are possible within the scope of the claimed invention,
and further additions, deletions, substitutions and modifications
may be made to the described embodiments without departing from the
scope of this disclosure.
* * * * *