ITTO20080448A1 - DETECTION OF MULTIPLE SIMULTANEOUS FREQUENCIES. - Google Patents

Description

DESCRIPTION of the industrial invention entitled "DETECTION OF MULTIPLE SIMULTANEOUS FREQUENCIES"

DESCRIPTION

Field of the Invention

This invention relates to "touch sensor panels" used as input devices for processing systems and, more specifically, to the use of multiple digital mixers to perform a spectral analysis of noise. and identifying low noise pacing frequencies, and using multiple pacing phases and frequencies to detect and locate touch events on a touch sensor panel.

Background of the Invention

There are currently many <types of> input devices for performing operations in a processing system, such as buttons or keys, mouse, trackball, touch sensor panels, joysticks, touch screens ("touch screens") and similar. Touch screens, in particular, are becoming increasingly popular due to their ease and versatility of operation as well as their falling price. Touch screens may include a touch sensor panel, which can be a free panel with a touch sensitive surface, and a display device which can be positioned behind the panel so that the touch sensitive surface can substantially cover The visible area of the display device. Touch screens can allow a user to perform various functions by touching the touch sensor panel using a finger, a stylus or another object in a position dictated by a user interface (UI) that is displayed by the device. display. In general, touch screens can recognize a touch event <0> and the location of the touch event on the touch sensor panel, and the processing system can then interpret the touch event according to the display that appears. at the time of the touch event, and then can perform one or more actions based on the touch event.

The touch sensor panels can be formed by a matrix of traces of rows and columns, with 0 pixel sensors present where the rows and columns cross each other being at the same time separated by a dielectric material. Each row can be driven by a stimulation signal, and the touch positions can be identified because the charge injected into the columns due to the stimulation signal is proportional to the touch quantity. However, the high voltage that may be required for the pacing signal may cause the sensor panel circuitry to be larger in size, and to be separated into two <0> more discrete integrated microcircuits ("chips"). In addition, the touch screens formed by display devices and capacitance-based touch sensor panels

like liquid crystal displays (LCDs, "Liquid Crystal Displays") can suffer from noise problems because the switching of the voltage required to operate an LCD can capacitively couple with the columns of the touch sensor panel and cause inaccurate measurements touch. Also, alternating current (AC) adapters used to power or charge the system can also cause noise coupling in the touch screen. Other noise sources may include switching power supplies in the system, backlight inverters, and light emitting diode (LED) pulse drivers. Each of these noise sources has a unique frequency and interference amplitude that can change over time.

Summary of the Invention

This invention relates to the use of multiple digital mixers for carrying out a noise spectral analysis and for the identification of low noise stimulation frequencies, and to the use of multiple stimulation phases and frequencies for the detection and localization of touch events on a touch sensor panel. Each of a plurality of sensing channels can be coupled to a column in a touch sensor panel and can have multiple mixers. Each mixer in each sense channel can use a circuit capable of being controlled to generate a demodulation frequency of a particular frequency, phase and delay.

When performing a spectrum analyzer function, no pacing signal is applied to any of the lines in the touch sensor panel. The sum of the output of all sensing channels, which can represent the total charge that is applied to the touch sensor panel including all detected noise, can be fed back to each of the mixers in each sensing channel. The mixers can be paired, and each pair of mixers can demodulate the overlap of all sensing channels using the in-phase (I) and quadrature (Q) signals of a particular frequency. The demodulated outputs of each pair of mixers can be used to calculate the magnitude of the noise at that particular frequency, where the smaller the magnitude, the less the noise at that frequency. Various low noise frequencies can be selected for use in a subsequent scan function of a touch sensor panel.

When performing the scan function of a touch sensor panel, in each of multiple phases, the various phases of the selected low noise frequencies can be used to simultaneously stimulate the lines of the touch sensor panel, and the multiple mixers in each. sensing channel can be configured to demodulate the signal received from the column connected to each sensing channel using the selected low-noise frequencies. It is therefore possible to save the demodulated signals coming from the multiple mixers. After all steps have been completed, the saved results can be used in the calculations to determine a touch image for the touch sensor panel at each frequency.

Brief Description of the Drawings

Figure 1 illustrates an exemplary processing system that can use multiple digital mixers to perform a noise spectral analysis and identify low-noise pacing frequencies, and that can use multiple pacing phases and frequencies to detect and locating the touch events on a touch sensor panel according to an embodiment of this invention.

Figure 2a illustrates a reciprocal capacitance touch sensor panel according to an embodiment of this invention.

Figure 2b is a side view of an exemplary pixel in a steady state (no touch) condition according to an embodiment of this invention.

Figure 2c is a side view of an exemplary pixel in a dynamic (touch) condition according to an embodiment of this invention.

Figure 3a illustrates a portion of a sense channel 0 of an exemplary event detection and demodulation circuit according to an embodiment of this invention.

Figure 3b illustrates a simplified block diagram of N detection channels <0> exemplary event detection and demodulation circuits according to an embodiment of this invention.

Figure 3c illustrates an exemplary block diagram of 10 detection channels which can be configured as a spectrum analyzer or panel scan logic according to an embodiment of this invention.

Figure 4a illustrates an exemplary time diagram representing an LCD phase and a touch sensor panel phase according to an embodiment of this invention.

Figure 4b illustrates an exemplary flow diagram describing the LCD phase and the touch sensor panel phase according to an embodiment of this invention.

Figure 4c illustrates an exemplary capacitive scan plane according to an embodiment of this invention.

Figure 4d illustrates exemplary calculations for a particular M channel for calculating full image results at different low noise frequencies according to an embodiment of this invention.

Figure Sa illustrates an exemplary mobile phone that can utilize multiple digital mixers to perform a noise spectral analysis and identify low-noise pacing frequencies, and that can use multiple pacing phases and frequencies to detect and locating touch events on a touch sensor panel according to an embodiment of this invention.

Figure Sb illustrates an exemplary digital audio player that can use multiple digital mixers to perform a noise spectral analysis and identify low-noise pacing frequencies, and that can use multiple pacing phases and frequencies to detect and locating the touch events on a touch sensor panel according to an embodiment of this invention.

Detailed Description of the Preferred <Realizzative> Form

In the following description of preferred embodiments, reference is made to the attached drawings which form part thereof, and in which specific embodiments with which the invention can be realized are represented by means of illustrations. and that structural changes can be made without departing from the scope of the embodiments of this invention.

This relates to the use of multiple digital mixers for carrying out a noise spectral analysis to identify low-noise stimulation frequencies, and to the use of multiple stimulation phases and frequencies to detect and locate touch events on a touch sensor panel. Each of a plurality of sensing channels can be coupled to a column in a touch sensor panel and can have multiple mixers. Each mixer in the sense channel can use a circuit capable of being controlled to generate a demodulation frequency of a particular frequency, phase and delay.

When performing a spectrum analyzer function, no pacing signal is applied to any of the lines in the touch sensor panel.

The sum of the output of all sensing channels, which can represent the total charge applied to the touch sensor panel including all detected noise, can be fed back to each of the mixers in each sensing channel. The mixers can be paired, and each pair of mixers can demodulate the sum of all sense channels using the <phase (I)> and quadrature <(0)> signals of a particular frequency. The demodulated outputs of each pair of mixers can be used to calculate the magnitude of the noise at that particular frequency, where <minor> and <magnitude, minor> and <the noise at that> frequency. Various low-noise frequencies can be selected for use in a subsequent scan function of a touch sensor panel.

When performing the scan function of a touch sensor panel, in each of multiple phases, various phases of the selected low noise frequencies can be used to simultaneously stimulate the lines of the touch sensor panel, and the multiple mixers in each channel. can be configured to demodulate the signal received from the column connected to each detection channel using the selected low noise frequencies. It is therefore possible to saly the demodulated signals coming from the multiple mixers. After all steps have been completed, the saved results can be used in calculations to determine a touch image for the touch sensor panel at each frequency.

While some embodiments of this invention may be described herein in terms of reciprocal capacitance touch sensors, it should be understood that the embodiments of this invention are not as limited but are generally applicable to other types of touch sensors such as self capacitance touch sensors. Further, although the touch sensors in the touch sensor panel can be described herein in terms of an orthogonal array of touch sensors having rows and columns, it should be understood that the embodiments of this invention are not limited to orthogonal arrays, but in general they can be applicable to touch sensors arranged in any number of dimensions and orientations, including random and three-dimensional orientations, in concentric and diagonal circles. In addition, the touch sensor panel described herein may be a single touch sensor panel ("singletouch") or a multi touch sensor panel ("multitouch"), the latter being described in the copending U.S. Application of Applicant no.

10 / 842,862 entitled "Multipoint Touchscreen", filed May 6, 2004 and published as US Published Application No. 2006/0097991 1'11 May 2006,

the contents of which are incorporated herein by citation.

Figure 1 illustrates an exemplary processing system 100 which can utilize multiple digital mixers for performing a noise spectral analysis and for identifying low noise stimulation frequencies, and which can utilize multiple stimulation phases and frequencies to detecting and locating the touch events on a touch sensor panel according to the embodiments of the invention. The processing system

100 may include one or more panel processors 102 and peripherals 104, and one panel subsystem 106. One or more panel processors 102 may include, for example, ARM968 processors or other processors with similar capabilities and functionality. However, in other embodiments, the functionality of the panel processor can be implemented instead by a dedicated logic, such as a state machine. The peripherals 104 may include, but are not limited to, a random access memory (RAM) or other types of memory or storage devices, surveillance timers and the like. The panel subsister 106 may include, but is not limited to, one <0> multiple sensing channels 108, a channel scan logic 110 and a drive logic 114. The channel scan logic 110 can access RAM 112 , independently read data from detection channels and provide control for detection channels. In addition, the channel scan logic 110 can control the drive logic 114 to generate pacing signals 116 at various phases and frequencies which can be selectively applied to the lines of a touch sensor panel 124. In some embodiments, the panel subsister 106, panel processor 102 and peripherals 104 may be integrated into a single application specific integrated circuit (ASIC).

A touch sensor panel 124 may include a capacitive sensing means having a plurality of row traces or drive lines and a plurality of column traces <0> sensing lines, although other sensing means may also be used. Row and column traces can be formed from a transparent conductive medium such as Indium Tin Oxide (ITO, "Indium Tin Oxide") or Antimony Tin Oxide (ATO, "Antimony Tin Oxide"), although others can also be used. transparent and non-transparent materials, such as copper. In some embodiments, the row and column traces may be perpendicular to each other, although other non-Cartesian orientations are possible in other embodiments. For example, in a polar coordinate system, the bearing lines may be concentric circles and the pilot lines may be radially extending lines (or vice versa). Therefore, it should be understood that the terms "row" and "column", "first dimension" and "second dimension", or "first axis" and "second axis" as used herein are intended to include not only orthogonal grids, but the intersecting traces of other geometric configurations having a first and a second dimension (eg the radial and concentric lines of a polar coordinate arrangement). The rows and columns can be formed on a single side of a substantially transparent substrate separated by a substantially transparent dielectric material, on opposite sides of the substrate, on two separate substrates divided by the dielectric material.

At the "intersections" of the traces, where the traces pass above and below (intersect) with each other (but they do not make direct electrical contact with each other), the traces can essentially form two electrodes ( although you can also intersect more than two tracks). Each intersection of the row and column traces can represent a capacitive sense node and can be seen as an image element (pixel) 126, which can be particularly useful when the touch sensor panel 124 is displayed while capturing an "image" of a touch. (In other words, after the panel subsystem 106 has determined whether a touch event has been detected in each touch sensor in the touch sensor panel, the configuration of touch sensors in the touch sensor panel where a touch event occurred touch can be displayed as an "image" of a touch (eg a configuration of fingers touching the panel)). The capacitance between the row and column electrodes appears as a parasitic capacitance when the given row is held at direct current (DC) voltage levels and as a reciprocal signal capacitance Csig when the given row is stimulated with an alternating current (AC) signal. . The presence of a finger 0 of another nearby object 0 on the touch sensor panel can be detected by measuring the changes in a charge signal Qsig present in the pixels that are touched, which is a function of Csig. Each column of the touch sensor panel 124 can drive a detection channel 108 (herein also referred to as an event detection and demodulation circuit) in a panel subsystem 106.

The processing system 100 may also include a main processor ("host") <128> for receiving the outputs from the panel processor 102 and for carrying out actions based on the outputs which may include LL, but are not limited. a L, moving an object such as a cursor 0 a pointer, 10 scrolling 0 panning, adjusting control settings 10, opening a file or a document, displaying a menu, making a selection , executing instructions, operating a peripheral device connected to the main device, answering a telephone call, making a telephone call, <la> terminating a telephone call, changing the volume 0 of the audio settings , storing information relating to telephone communications such as <addresses,> numbers dialed <frequently, calls> received, missed calls, connecting to a computer or to an el aboratori, allowing authorized persons to access limited areas of the computer or computer network, loading a user profile associated with a preferred disposition of the desktop computer user, allowing access to web content, launching a particular program, encrypting or decrypting a message, and / or the like. The main processor 128 may also perform additional functions which may not be related to panel processing, and may be coupled to a program storage device 132 and a display device 130 such as an LCD display for providing a UI to a device user.

In some systems, the sensor panel 124 may be driven by a high voltage drive logic. The high voltages that may be required by the high voltage driving logic (e.g. 18 V) can force to form the driving logic

at high voltage separately from the panel subsystem 106, which can operate at much lower digital logic voltage levels (e.g. 1.7 to 3.3 V). However, in embodiments of the invention, a driving logic on the microcircuit ("onchip") 114 can replace the high voltage driving logic outside the microcircuit ("offchip"). Although the panel subsystem 106 may have supply voltages at low digital logic levels, the driving logic on the microcircuit 114 can generate a higher supply voltage than the supply voltages at digital logic levels by putting two transistors together in cascode configuration to form a charge pump 115. The charge pump 115 can be used to generate stimulation signals 116 (Vstim) which can have amplitudes of approximately twice the supply voltages at digital logic levels (e.g. 3.4 to 6 , 6 V). Although Figure 1 represents the charge pump 115 separate from the driving logic 114, the charge pump can be part of the driving logic.

Figure 2a illustrates an exemplary reciprocal capacitance touch sensor panel 200 according to embodiments of the invention. Figure 2a indicates the presence of a parasitic estray capacitance in each pixel 202 positioned at the intersection of a row trace 204 and a column trace 206 (although in Figure 2a estray is shown only for one column for purposes of simplification In the example of the Figure, stimuli in CA Vstim 214, Vstim 215 and Vstim 217 can be applied to various lines, while other lines can be connected to CC. Vstim 214, Vstim 215 and Vstim 217 can be in phases and frequencies different, as will be explained below. Each stimulation signal on a row can cause a charge Qsig = Csig x vstim to be injected into the columns through the reciprocal capacitance present in the affected pixels. injected (Qsig_sense) when a finger, palm or another object is present in one <0> pHi. of the affected pixels. Vstim signals 214, 215 and 217 may include a 0 pHi. and sinusoidal. Note that although Figure 2a illustrates rows 204 and columns 206 as substantially perpendicular, they do not need to be aligned, as described above. As described above, each column 206 can be connected to a sense channel (see the sense channels

108 in Figure 1).

Figure 2b is a side view of an exemplary pixel 202 in a steady state (no touch) according to the embodiments of the invention. In Figure 2b, an electric field of electric field lines 208 of the reciprocal capacitance between the traces of row 204 and column 206 or the electrodes separated by a dielectric 210 is represented.

Figure 2 is a side view of an exemplary pixel 202 in a dynamic (touch) condition. In Figure 2c, a finger 212 is placed close to a pixel 202. The finger 212 is a low impedance object at signal frequencies, and has a

AC Cfinger from the trace of column 204 to the body. The body has a proper capacitance with respect to Cbody mass of about 200 pF, where Cbody is much greater than Cfinger. Well finger 212 blocks some electric field lines 208 between the row and column electrodes (those fringing fields that come out of the dielectric and pass through the air above the row electrode), those electric field lines are derived a mass through the path of capacities inherent in the finger and body and,

as a result, the steady-state signal capacity Csig is reduced for ｾ ｃ ｳ ｩ ｧ Ｎ In other words, the combined capacity of the finger and body acts to reduce Csig by a quant.i t.a <ｾ ｃ ｳ ｩ ｧ> (which here can also be called Csig_sense), and can act as a dynamic return path <0> of shunt to ground, blocking some of the electric fields resulting in a reduced net signal capacity. The signal capacity in the pixel becomes Csig <ｾ ｃ ｳ ｩ ｧ Ｌ> where Csig represents the static component (no touch) and <ｾ ｃ ｳ ｩ ｧ> represents the dynamic component (touch). Note that Csig -

<ｾ ｃ ｳ ｩ ｧ> can always be non-null due to the inability of a finger, palm or other object to block all electric fields, especially those electric fields that remain entirely within the dielectric material. In addition, it should be understood that as a finger is pushed harder <0> pHi completely on the multi-touch panel, the finger may tend to flatten, blocking an ever-increasing amount of electric fields, and <COS1.ｾ ｃ ｳ ｩ ｧ> can be variable and representative of how fully the finger is pressing in aul, panel (ie a range from "no touch" to "full touch").

Figure 3a illustrates a portion of an exemplary detection channel 0 event detection and demodulation circuit 300 according to embodiments of the invention. One <0> multiple sense channels 300 may be present in the panel subsystem. Each column from a touch sensor panel may be connected to a sense channel 300. Each sense channel 300 may include a virtual ground amplifier 302, an amplifier output circuit 309 (to be explained in more detail below), a signal mixer 304 and an accumulator 308. Note that the amplifier output circuit 309 can also be connected to other signal mixers and associated circuitry not shown in Figure 3 to simplify the figure.

The virtual ground amplifier 302, which can also be called a DC amplifier <0> charge amplifier, can include a feedback capacitor Cfb

and a feedback resistor Rfb. In some embodiments, due to the much smaller amount of charge that can be injected into a row due to lower Vstim amplitudes, Cfb can be made much smaller than in some previous designs. However, in other embodiments, since as many as all lines can be stimulated simultaneously at the same time, which tends to add charge, non-reduced Cfb in size.

Figure 3a represents, in dashed lines, the total steady state signal capacitance Csig_tot to which a touch sensor panel column connected to a sensing channel 300 may contribute when applying a <0> pHi. Vstim input stimuli to one or more lines in the touch sensor panel and no finger, palm or other object. In a steady-state, no-touch condition, the total Qsig_tot signal charge injected into the column is the sum of all charge injected into the column from each stimulated row. In other words, Qsig_tot = E (Csig * Vstim for all the stimulated lines). Each detection channel coupled to a column can detect any change in total signal charge due to the presence of a finger, palm, and other body part <0> object in one <0> multiple pixels in that column. In other words, Qsig_tot_sense = E ((CsigCsig_sense) * Vstim for all stimulated lines).

As indicated above, there may be an inherent parasitic capacitance Cstray in each pixel on the touch sensor panel. In a virtual ground charge amplifier 302, with the (non-inverting) input connected to a reference voltage Vref, the (inverting) input can also be driven at Vref, and a DC operating peak can be established. Therefore, regardless of how much Csig is present at the input of the virtual mass charge amplifier 302, the input can be driven at Vref. Due to the characteristics of the virtual mass charge amplifier 302, any Qstray charge that is stored in the Cstray is constant, because the voltage across the Cstray is held constant by the charge amplifier. Therefore, regardless of how much parasitic capacitance Cstray added to the input, the net charge in Cstray will always be zero. Consequently, the input charge is zero when the corresponding row is held at CC and is simply a function of Csig and Vstim when the corresponding row is stimulated. In one case, then, that there is no charge through Csig, the parasitic capacitance is discarded, and essentially eliminated from any equation. Thus, even with one hand over the touch sensor panel, although Cstray may increase, the output will not be affected by the Cstray change.

The gain of the virtual ground amplifier 302 can be small (e.g. 0.1) and can be calculated as the ratio between Csig_tot and the feedback capacitor Cfb. The adjustable feedback capacitor Cfb can convert the charge Qsig into the voltage vout. The Vout output of the virtual ground amplifier 302 is a voltage which can be calculated as the ratio between Csig / Cfb multiplied by Vstim referred to Vref. For example, the Vstim signaling may appear at the output of the virtual ground amplifier <302> as signals having a much smaller amplitude. However, when a finger is present, the amplitude of the output can be reduced even further, because the signal capacity is reduced for 6Csig. The output of the charge amplifier 302 is the superposition of all the row stimulus signals multiplied by each of the Csig values on the column associated with that charge amplifier. A column may have some pixels that are driven by a positive phase frequency, and simultaneously have other pixels that are driven by that same negative phase frequency (0 180 degrees out of phase). In this case, the total component of the charge amplifier output signal at that frequency may be the amplitude and phase associated with the sum of the product of each of the Csig values multiplied by each of the stimulus waveforms. For example, if two lines are positive phase driven, and two lines are negative phase driven, and the values of Csig are all equal, then the total output signal will be zero. B and the finger approaches one of the pixels which are positive phase driven, and the associated Csig decreases, then the total output at that frequency will have a negative phase.

Vstim, as applied to a line in the touch sensor panel, can be generated as a burst of sine waves (e.g. sine waves with smoothly changing amplitudes in order to be spectrally narrow) or another non-DC signal in otherwise a DC signal, although in some embodiments the sine waves representing Vstim may be preceded and followed by other non-DC signaling. If Vstim is applied to a row and having a signal capacitance in a column connected to a sensing channel 300, the output of the charge amplifier 302 associated with that particular stimulus may be a train of sine waves 310 centered at Vref with a peak-to-peak arnpitude ｾ ｰ Ｍ ｰ Ｉ in the steady state condition which can be a fraction of the pp amplitude of Vstim, the fraction corresponding to the gain of the charge amplifier 302. For example, if Vstim includes sine waves of 6.6 V pp and the charge amplifier gain is 0.1, then the charge amplifier output associated with this row may be approximately a sine wave of 0.67 V pp. Bi should note that the signals from all lines are superimposed at the output of the prearnplifier. The analog output from the pre-amplifier is converted to digital in block 309. The output from 309 PUQ be mixed in a digital signal mixer 304 (which is a digital multiplier) with an Fstim 316 demodulation waveform.

Since Vstim can create undesirable harmonics, especially if formed by square waves, the demodulation waveform Fstim 316 can be a Gaussian sine wave that can be digitally generated by a numerically controlled oscillator (NCO, "Numerically Controlled Oscillator"). ) 315 and synchronized with Vstim. It should be understood that in addition to the NCO 315, which are used for digital demodulation, independent NCOs can be connected to digital to analog converters (DACs, "DigitaltoAnalog Converter"), whose outputs can be optionally inverted and used as a stimulus for line. The NCO 315 can include a numerical control input to set the output frequency, a control input to set the delay, and a control input to enable the NCO to generate a signal in phase (I) <0> in <frame> (Q). The signal mixer 304 can demodulate the output of the charge amplifier 310 by subtracting Fstim 316 from the output to provide better noise rejection. The signal mixer 304 can reject all frequencies outside the passband, which in one example may be about +/- 30kHz around Fstim. This noise rejection can be beneficial in a noisy environment with many noise sources, such as 802.11, Bluetooth and the like, all having some characteristic frequency that can interfere with the sensitive sensing channel (at the femtofarad level) 300. For each frequency Of interest which is demodulated, the signal mixer 304 is essentially a synchronous rectifier where the frequency of the signal at its inputs itself and, as a result, the output of the signal mixer 314 is essentially a rectified Gaussian sine wave.

Figure 3b illustrates a simplified block diagram of N detection channels or exemplary event detection and demodulation circuits 300 according to embodiments of the invention. As indicated above, each charge amplifier or programmable gain amplifier (PGA) 302 in a sense channel 300 can be connected to an amplifier output circuit 309, which in turn can be connected to R signal mixers 304 through multiplexer 303. Amplifier output circuit 309 may include anti-aliasing filter 301, ADC 303, and result register 305. Each signal mixer 304 may be demodulated with a signal from an NCO 315. The demodulated output of each signal mixer 304 may be connected to a separate accumulator 308 and a result register 307.

It should be understood that the PGA 302, which may have detected a higher amount of charge generated by a high voltage Vstim signal (e.g. 18 V) in previous designs, can now detect a smaller amount of charge generated. from a lower voltage Vstim signal (e.g. 6.6 V). Furthermore, the NCOs 315 can cause the output of the charge amplifier 302 to be demodulated simultaneously and yet differently, but each NCO 310 can generate signals at different phases, delays and frequencies. Each signal mixer 304 in a particular sensing channel 300 percent can generate an output representative of approximately one Resimo of the charge from previous designs, but since there are R mixers, each demodulating to a different frequency, each sensing channel puC > still detect about the same total amount of charge as in previous projects.

In Figure 3b, the signal mixers 304 and accumulators 308 can be implemented digitally instead of in analog circuitry within an ASIC. Having the mixers and accumulators implemented digitally instead of in an analog circuitry inside the ASIC can save about 15% in die space.

Figure 3c illustrates an exemplary block diagram of 10 detection channels 300 which can be configured as a spectrum analyzer or as a panel scan logic according to the embodiments of the invention. In the example of Figure 3c, each of the 10 sensing channels 300 can be connected to a separate column in a touch sensor panel. Note that each sense channel 300 may include a multiplexer <0> a switch 303, to be explained in further detail below. The solid line connections in Figure 3c can represent the sense channels configured as panel scan logic, and the dashed line connections can represent the sense channels configured as a spectrum analyzer. Figure 3c will be discussed in more detail below.

Figure 4a illustrates an exemplary time diagram 400 representing an LCD phase 402 and the vertical blanking 0 sensor panel phase 404 according to embodiments of the invention. During the LCD 402 phase, the LCD may be actively switching and may be generating the voltages necessary to generate <The> images. At this time no panel scan has been performed. During the touch sensor panel step 404, the detection channels can be configured as a spectrum analyzer to identify low noise frequencies, and can also be configured as a panel scan logic to detect and locate an image of a touch.

Figure 4b illustrates an exemplary flowchart 406 describing the LCD phase 402 and the touch sensor panel phase 404 corresponding to the example of Figure 3c (the present example) according to embodiments of the invention. In Phase 0, the LCD CAN be updated as described above.

Phases 1 to 3 can represent a 406 low noise frequency identification phase. In Phase 1, the detection channels can be configured as a spectrum analyzer. The purpose of the spectrum analyzer is to identify various low-noise frequencies for later use in a panel scan. With no pacing rate applied to any of the touch sensor panel lines, the sum of the output of all sensing channels, which represents the total charge that applied to the touch sensor panel including all detected noise, can be provided. in feedback to each of the mixers in each sensing channel. The mixers can be paired, and each pair of mixers can demodulate the sum of all detection channels using the in-phase (I) and quadrature (Q) signals of a particular frequency. The demodulated outputs of each pair of mixers can be used to calculate the magnitude of the noise at that particular frequency, where the smaller the magnitude, the less the noise at that frequency.

In Step 2, the process of Step <1> can be repeated for a different set of frequencies.

In Step 3, various low noise frequencies can be selected for use in a subsequent touch sensor panel scan by identifying those frequencies that produce the lowest calculated magnitude value.

Steps 4 to 19 may represent a panel scan step 408. In Steps 4 to 19, the detection channels can be configured as panel scan logic. In each of Phases 4 to 19, various phases of the selected low-noise frequencies can be used to simultaneously stimulate the rows of the touch sensor panel, and the multiple mixers in each sensing channel can be configured to demodulate the signal received by the column. connected to each detection channel using the selected low noise frequencies. <Then demodulated signals from multiple mixers can be saved.

In Step 20, after all steps have been completed, the saved results can be used in the calculations to determine a touch survey for the touch sensor panel in each of the selected low noise frequencies.

Again referring to the actual example as shown in Figure 3c, while the sensing channels 300 are configured as a spectrum analyzer, no pacing signal is applied to any of the lines in the touch sensor panel. In the present example, there are 10 columns and paths or 10 sensing channels 300, and three mixers 304 for each sensing channel 300, for a total of 30 mixers. The outputs of all amplifier output circuits 309 in each sense channel 300 can be sounded together using a sonuna 340 circuit, and supplied to all mixers 304 through a multiplexer 0 switch 303, which can be configured to select the output of the sonuna 340 circuit instead of the charge amplifier 302.

While the detection channels are configured as a spectrum analyzer, the background coupling on the columns can be measured. Since no vstim is applied to any line, there is no Csig in any pixel, and any swiping on the panel should not affect the result of the noise (unless finger <0> another object making 10 swipes pairs the noise on the rnassa). By summing together all the outputs of all the amplifier output circuits 309 in an adder 340, a digital bit stream representing the total noise received in the touch sensor panel can be obtained. The frequencies of the noise and the pixels in which the noise is being generated are not known a priori to the spectral analysis, but they become known after the spectral analysis is completed. The pixel in which the noise is being generated is not known and is not recovered after the spectral analysis, since the bit stream is being used as a general noise collector, they do not need to be known.

While configured as a spectrum analyzer, the 30 mixers in the example of Figure 3c can be used in 15 pairs, each pair demodulating the I and Q signals for 15 different frequencies generated by the

NCO 315. These frequencies can be, for example, between 200 kHz and 300 kHz. The NCO 315 can produce a digital ramp sine wave which can be used by the digital mixers 304 to demodulate the noise output of the sum circuit 340. For example, I 'Nca 315 0 A can generate the I component of frequency FO , while the NCa 315 0 B can generate the Q component of FO. Similarly, the NCa 315 0 C can generate the I component of frequency F1, the NCa 315 1 A can generate the Q component of F1, the NCa 315_1_B can generate the I component of frequency F2, the NCa 315 1 C can generate the Q component of F2, etc.

The output of the summing circuit 340 (the noise signal) can then be demodulated by components I and Q from FO to F14 using 15 pairs of mixers. The result of each mixer 304 can be accumulated in the accumulators 308. Each accumulator 308 can be a digital register which, over a sampling time period, can accumulate (add together) the instantaneous values from the mixer 304. At the end of the sampling period sampling time, the accumulated value represents the amount of noise signal at that frequency and phase.

The accumulated results of a demodulation in I and Q at a particular frequency can represent the amount of content at that frequency that is in phase 0 in quadrature. These two values can then be used in a phase and magnitude computation circuit 342 to find the absolute value of the total magnitude (amplitude) at that frequency. A larger magnitude may indicate a higher background noise level at that frequency. The magnitude value calculated by each phase and magnitude computation circuit 342 <can be saved. Note that without the Q component, noise that was out of phase with the demodulation frequency may remain undetected.

This whole process can be repeated for 15 different frequencies from F15 to F29. You can then compare the saved magnitude values for each of the 30 frequencies, and you can choose the three frequencies with the lowest magnitude values (and therefore with the lowest noise levels), called here frequencies A, Bee. In general, the number of low noise frequencies chosen may correspond to the number of mixers in each detection channel.

Still referring to Figure 3c, when the detection channels 300 are configured as panel scan logic, the dashed lines in Figure 3c can be ignored. In each of Phases 4 to 19, various phases of the selected low-noise frequencies can be used to simultaneously stimulate the rows of the touch sensor panel, and the multiple mixers in each sensing channel can be configured to demodulate the signal received by the column. connected to each sensing channel using the selected low noise frequencies A, B and C. In the example of Figure 3c,

<NCO 0 A can generate> a frequency A, NCO 0 B can <generate a frequency> B, NCO 0 C can generate <a> frequency C, NCO 1 A can generate a frequency A,

NCO 1 B can generate a frequency B, NCO 1 C can generate a frequency C, etc. The demodulated signals from each mixer 304 in each sense channel can then be accumulated in accumulators 308, and saved.

In general, Ie <R> mixer outputs for any sensing channel M (where M = 0 to Nl) demodulated by R low-noise frequencies Fa 'FlFR l can be represented by the notation xFaS [chM], xF1S [chM]

xFR_1S [chM], where xFar represents the output of a demodulated mixer with the frequency Fa 'xFl represents the output of a demodulated mixer with the frequency Fl <,> xFR_ l represents the output of a demodulated mixer with the frequency FR l <, > and S represents the sequence number in the panel scan step.

Therefore, in Step 4 (which represents sequence number 1 in the panel scan step), and using the low noise frequencies A, Bee as demodulation frequencies, the outputs to be saved can be called xa1 [chO], xb1 [ chO], xc1 [chO], xa1 [ch1], <xb1 [ch1], xc1 [chl],> xaJ. [ch9], xb1 [ch9], xc1 [ch9]. Thus, in the current example, in the Phase 4 30 results are saved. In Phase 5 (representing sequence number 2 in the panel scan phase), the 30 results to be saved can be called xa2 [chO], xb2 [chO], xc2 [chO], xa2 [ch1], xb2 [ch1 ], xc2 [ch1], xa2 [ch9], xb2 [ch9], xc2 [ch9]. The 30 outputs to be saved in each of Phases 6 to 19 can be called in a similar way.

It should be understood that the additional logic outside the sense channels in Figure 3c can be implemented in the channel scan logic

<110 of Figure> 1, although it can also <be> located elsewhere.

Figure 4c illustrates an exemplary capacitive scan plane 410 corresponding to the current example according to embodiments of the invention. Figure 4c describes Steps 0 to 19 as shown in Figure 4b for an exemplary sensor panel having 15 rows RO to R14.

Phase 0 can represent the phase of LCD in which time the LCD can be updated. The LCD phase can take about 12 ms, a time during which no line can be stimulated.

Steps 1 to 19 can represent the vertical blanking interval for the LCD, a time during which the LCD is not changing voltages.

Phases 1 to 3 can represent the low noise frequency identification phase which can take about 0.6 ms, again a time during which no line can be stimulated. In Phase 1, I and Q components of different frequencies varying from 200

kHz to 300 kHz (separated by at least 10 kHz) can be applied simultaneously to pairs of mixers in the detection channels configured as a spectrum analyzer, and a noise magnitude can be saved at those frequencies. In Step 2, <Le> components I and <Q> of different frequencies ranging from 300 kHz to 400 kHz can be applied simultaneously to pairs of mixers in the detection channels configured as spectrum analyzer, and a noise magnitude can be saved at those frequencies. In Step 3, the lowest noise frequencies A, Bee can be identified by locating the frequencies that produced the lowest saved quantities. The identification of the lowest noise frequencies can be performed only on the spectra measured in phases 1 and 2, or it can also take into consideration the historical measurements obtained from phases 1 and 2 of previous plots.

Steps 4 to 19 may represent the panel scan step which may take approximately 3.4 ms.

In Phase 4, which can take about 0.2 ms, the positive and negative phases of A, B and C can be applied to some lines, while other lines can be left unstimulated. It should be understood that A can represent the scan frequency A with a positive phase, A can represent the scan frequency A with a negative phase, B can represent the scan frequency B with a positive phase, B can represent the scan frequency B with a negative phase, <+ C> can represent the scan frequency

<C> with a positive phase, and <C> can represent the scan frequency C with a negative phase. The charge amplifiers in the sense channels coupled to the sensor panel columns can sense the total coupled charge on the column due to the rows being stimulated. The output of each charge amplifier can be demodulated by the three mixers in the sense channel, each mixer receiving the demodulation frequency A, B

or C. The results can be obtained and saved <0> the values xal, xbl and xCI, where xal, xbl and xc i are vectors. For example, xa1 can be a vector with 10 values xa1 [chO], xa1 [ch1], xa1 [ch2] xa1 [ch9], xb1 can be a vector with 10 values xb1 [chO], xb1 [ch1], xb1 [ ch2] xb1 [ch9], and xc1 can be a vector with 10 values xc1 [chO], xC1 [ch1], xc1 [ch2] xc1 [ch9].

In particular, in Phase 4, A is applied to lines 0, 4, 8 and 12, B, B, B and B are applied respectively to lines 1, 5, 9 and 13, C, C, C and C are applied respectively lines 2, 6, 10 and 14, and no stimulation is applied to lines 3, 7, 11 and 15. The detection channel connected to the column 0 detects the charge that is injected into column 0 from all the stimulated lines, at the phases and frequencies indicated. The three mixers in the sensing channel can now be set to demodulate A, B and <C,> and three different vector results xa1, xb1 and xc1 can be obtained for the sensing channel. For example, the vector xa1 can represent the sum of the charge injected in columns 0 to 9 in the four lines that are stimulated by A (eg Ie lines 0, 4, 8 and 12). Vector xa1 does not provide complete information, however, as the particular line in which a swipe occurred is not yet known. In parallel, in Phase 4, rows 1 and 5 can be stimulated with B, and rows 9 and 13 can be stimulated with B, and vector xb1 can represent the sum of the charge injected into columns 0 to 9 in the rows that are stimulated by B and B (eg lines 1, 5, 9 and 13). In parallel, in the same Phase 4, lines 2 and 14 can be stimulated with C, and lines 6 and 10 can be stimulated with C, and the vector xc1 PUQ represent the

sum of the charge injected in columns <da> 0 to 9 in the rows that are stimulated by C and by C (eg Ie rows 2, 6, 10 and 14). Thus, at the conclusion of Phase 4, three vectors containing 10 results each are obtained and stored, for a total of 30 results.

Steps 5 to 19 are similar to Step 4, except that different steps of A, B and C can be applied to different lines, and different vector results are obtained in each step. At the conclusion of Phase 19, a total of 480 results will have been obtained in the example of Figure 4c. Obtaining the 480 results in each of the Phases 4 to 19, a factorial, combinatorial approach is used, in which for each pixel information is obtained incrementally regarding the image of a touch for each of the three frequencies A, B and C.

It should be noted that Stages 4 to 19 illustrate a combination of two distinctive elements, a multiphase scan and a multi-frequency scan.

<Each element> distinctive can have its own benefit. Multi-frequency scanning can save time for a factor of three, while multiphase scanning can provide a better signal-to-noise ratio (SNR) for about a factor of two.

Multiphase scanning can be employed by simulating most <0> all lines using different phases of multiple frequencies. The multiphase scan is described in the copending U.S. Dornanda of Applicant no.

11 / 619,433 entitled "Simultaneous Sensing Arrangement", filed on January 3, 2007, the contents of which are incorporated herein by reference. One benefit of multiphase scanning is that more information can be obtained from a single panel scan. Multi-phase scanning can obtain a more accurate result because it minimizes the possibility of inaccuracies that can be produced due to certain alignments of the noise phases and the stimulation frequency.

In addition, multifrequency scanning may be employed to stimulate most or all lines simultaneously using multiple frequencies. As mentioned above, multi-frequency scanning saves time. For example, in some previous procedures, you can scan 15 lines in 15 steps at frequency A, then you can scan 15 lines in 15 steps at frequency B, then you can scan 15 lines in 15 phases at l The frequency C, for a total of 45 phases. However, using a multi-frequency scan as shown in the example of Figure 4c, only a total of 16 steps (Step 4 to Step 19) may be required. The multifrequency in its simplest embodiment can include the simultaneous scanning of RO at frequency A, of Rl at frequency B, and of R2 at frequency C in a first phase, then the simultaneous scanning of Rl at frequency A, of R2 at frequency B, and from R3 to I The frequency C in phase 2, etc. for a total of 15 phases.

At the conclusion of Steps 4 to 19, when the 480 results described above have been obtained and stored, additional calculations can be made using these 480 results.

Figure 4d illustrates exemplary calculations for a particular M channel for calculating the results of a complete image at different low noise frequencies corresponding to the current example according to embodiments of the invention. In the current example, for each channel M, where M 0 to 9, the 45 calculations depicted in Figure 4d can be performed to obtain a row result for each row and each frequency A, B and C. Each set of 45 calculations for each channel it can generate a resulting pixel value for the column of pixels associated with that channel. For example, the calculation of frequency A, Line 0, (xa1 [chM] xa2 [chM] xa3 [chM] xa4 [chM]) / 4 can generate the result of channel M, line 0, for frequency A. In the current example, after all calculations have been made and stored for each channel, a total of 450 results will have been obtained. These calculations correspond to Phase 20 of Figure 4b.

Of these 450 results, there will be 150 for frequency A, 150 for frequency B, and 150 for frequency C. The 150 results for a particular frequency represent an image map or a touch image at that frequency. since it is provided a unique value for each column (c <Loe> channel) and row intersection. These touch images can then be processed by software that synthesizes the three images and looks at their characteristics to determine which frequencies are intrinsically noisy and which frequencies are intrinsically clean. Then further processing can be carried out. For example, if all three frequencies A, Bee are relatively noise-free, the results can be averaged together.

It should be understood that the calculations shown in Figures 4c and 4d can be performed under the control of the panel processor 102 0 of the main processor 128 of Figure 1, although they can also be performed elsewhere.

Figure 5a illustrates an exemplary mobile phone 536 which PUQ includes a touch sensor panel 524, a display device 530 bonded to the sensor panel using a pressure sensitive adhesive (PSA) 534, and other blocks. of a processing system in a processing system 100 of Figure 1 for applying multiple pacing phases and rates to the touch sensor panel to identify pacing rates

low noise and for detecting and locating touch events according to embodiments of the invention.

Figure 5b illustrates an exemplary digital audio / video player 540 which may include a touch sensor panel 524, a display device 530 joined to the sensor panel using pressure sensitive adhesive (PSA) 534, and other system blocks of processing in a processing system 100 of Figure 1 for applying multiple pacing phases and frequencies to the touch sensor panel to identify low-noise pacing frequencies

and for detecting and locating touch events according to embodiments of the invention.

While embodiments of this invention have been fully described with reference to the accompanying drawings, it should be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the embodiments of this invention as defined by the appended claims.

WHAT IS CLAIMED IS:

1. A method for obtaining a plurality of values used to generate a touch image from a touch sensor panel, comprising:

the simultaneous application of a plurality of stimulation frequencies having positive and negative phases

to a plurality of control lines of the touch sensor panel in a particular distribution;

receiving a signal from each of a plurality of sensing lines of the touch sensor panel in a different sensing channel; demodulating the signal received in each detection channel with a plurality of demodulation frequencies, the demodulation frequencies being the same frequencies as the in-phase stimulation frequencies;

accumulating the demodulated signals with the plurality of demodulation frequencies in each detection channel to generate a plurality of values representing the demodulated signals accumulated for each detection channel; And

the memorization of the plurality of values for all

the detection channels.

2. The process of claim 1, comprising

Claims (1)

furthermore the repetition of the steps of Claim 1 a multiplicity of times and the memorization of the many pluralities of values after the simultaneous application of the plurality of stimulation frequencies having positive and negative phases to the plurality of control lines of the touch sensor panel in multiple unique distributions. The method of Claim 2, further comprising, for each of the plurality of detection lines, the calculation and storage of a driving line result for each driving line and for each of the plurality of frequencies using the plurality of stored values . The process of Claim 2, wherein the plurality of demodulation frequencies are selected low noise frequencies. 5. The process of Claim 1, further comprising obtaining the plurality of values during the vertical erasing step of a liquid crystal display (LCD) adjacent the touch sensor panel. 6. In a system including a sensor panel having a plurality of drive lines which are driven simultaneously with a plurality of pacing frequencies having positive and negative phases in a particular distribution, a method of obtaining a plurality of values used for generate a touch image, the method comprising: demodulating a sense signal received on each sense line of the sensor panel with a plurality of demodulation frequencies, the demodulation frequencies being the same frequencies as the pacing frequencies but in phase; And The accumulation of each of the plurality of demodulated sense signals for each sense line to generate the plurality of values representing the accumulated demodulated sense signals. 7. The process of Claim 6, the plurality of driving lines on the touch sensor panel being driven simultaneously with the plurality of stimulation frequencies having positive and negative phases in multiple unambiguous distributions in sequence, the method further comprising: the storage of multiple plurality of values after the simultaneous application of the plurality of stimulation frequencies having positive and negative phases to the plurality of control lines of the touch sensor panel in multiple univocal distributions. 8. The process of Claim 7, further comprising, for each of the plurality of detection lines, the calculation and storage of a driving line result for each driving line and for each of the plurality of frequencies using the multiple pluralities of stored values. The process of Claim 7, wherein the plurality of demodulation frequencies are selected low noise frequencies. 10. The process of Claim 6, further comprising obtaining the plurality of values during the vertical blanking step of a liquid crystal display (LCD) adjacent the touch sensor panel. 11. Apparatus for obtaining a plurality of values used to generate a touch image from a touch sensor panel, comprising: a plurality of sensing channels, each sensing channel including a charge amplifier configured to receive a signal from a different sensing line of the touch sensor panel, a plurality of mixers coupled to an output of the multiplexer, a frequency generator circuit coupled to each of the plurality of mixers for generating a demodulation frequency, e an accumulator coupled to each of the plurality of mixers for generating a value representing an accumulated mixer output; wherein each frequency generator circuit in each sense channel generates a different demodulation frequency, the different demodulation frequencies corresponding to different pacing frequencies applied simultaneously with different phases to the drive lines of the touch sensor panel. 12. The apparatus of claim 11, one or more of the frequency generating circuits comprising a numerically controlled oscillator (NCO). 13. Apparatus of claim 11, further comprising a memory for storing the plurality of values generated by each detection channel. <14.> The apparatus of <Claim 13,> further comprising a processor for calculating and storing, for each of the plurality of detection lines, a driving line result for each driving line and for each of the plurality of frequencies of demodulation using the plurality of stored values. 15. Processing system comprising the apparatus of Claim 11. 16. Mobile telephone comprising the processing system of Claim 15. 17. Digital audio player comprising the processing system of Claim 15. 18. A method of operating a touch screen, the touch screen having a touch sensor panel and a display device, the method comprising: updating the display device during an active period of the display device; And obtaining a touch image from the touch sensor panel during a vertical erasing step of the display device. 19. The process of Claim 18, wherein the display device is a liquid crystal display (LCD). 20. System for obtaining a plurality of values from a touch sensor panel, the plurality of values for generating a touch image, the system comprising: a touch sensor panel having a plurality of driving lines and a plurality of sensing lines; And an integrated circuit coupled to the touch sensor panel, including a driving logic configured for generating a plurality of pacing signals to the plurality of driving lines, the driving logic including a charge pump configured for converting a low level supply voltage for the integrated circuit into a higher level supply voltage, the drive logic further being configured to convert the higher level supply voltage into pacing signals of reduced amplitude, and a plurality of sensing channels, each sensing channel including a charge amplifier configured to receive a sensing signal from a different sensing line of the touch sensor panel, the plurality of sensing channels for generating the plurality of values from the received sense lines, the plurality of values representing a plurality of accumulated mixer outputs; wherein each charge amplifier in each sense channel includes a reduced feedback capacitance whose physical dimension scaled downward according to a smaller amount of charge injected onto the sense lines by the reduced amplitude stimulation signals. 21. The system of Claim 20, each detection channel further comprising: a plurality of mixers coupled to an output of the multiplexer; a frequency generator circuit coupled to each of the plurality of mixers for generating a demodulation frequency; And an accumulator coupled to each of the plurality of mixers for generating the values representing the accumulated mixer outputs; wherein each frequency generating circuit generates a different demodulation frequency, the different demodulation frequencies corresponding to different stimulation frequencies applied simultaneously to the drive lines of the touch sensor panel. 22. The system of Claim 21, one or more of the frequency generating circuits comprising a numerically controlled oscillator (NCO). 23. The system of Claim 21, further comprising a memory for storing the plurality of values generated by each detection channel. 24. The system of Claim 23, further comprising a processor for calculating and storing, for each of the plurality of sense lines, a driver line result for each driver line and for each of the plurality of demodulation frequencies using the plurality of values stored. 25. Processing system comprising the system of Claim 21. 26. Mobile telephone comprising the processing system of Claim 25. 27. Digital audio player comprising the processing system of Claim 25. 28. Process for obtaining a p.Lura.Ld t.a of values from a touch sensor panel, the plurality of values for generating a touch image, the process comprising: The use of a charge pump inside an integrated circuit to convert a low level supply voltage for the integrated circuit into a higher level voltage, The use of the higher level voltage to generate stimulation signals of reduced amplitude within the integrated circuit, the stimulation signals of reduced amplitude for driving a plurality of driving lines in a touch sensor panel; receiving a detection signal from from each of a plurality of sense lines in the touch sensor panel in a charge amplifier in each of a plurality of sense channels within the integrated circuit, the plurality of sense channels for generating the plurality of values from the received sense signals, the plurality of values representing a plurality of accumulated mixer outputs; And the utilization of a reduced feedback capacity in each charge amplifier whose physical size is scaled down according to a smaller amount of charge injected onto the sense lines by the reduced amplitude stimulation signals. <29.> The process of <Claim 28,> further comprising: demodulating the sense signal received in each sense channel using a plurality of different demodulation frequencies, the different demodulation frequencies corresponding to different pacing frequencies applied simultaneously to the drive lines of the touch sensor panel; And accumulating the demodulated sense signals in each sense channel to generate the plurality of values. The method of Claim 29, further comprising the generation of demodulation frequencies for demodulating the received sense signals using one or more numerically controlled oscillators (NCOs). 31. The method of Claim 28, further comprising storing the plurality of values generated by each sensing channel, and calculating and storing, for each of the plurality of sensing lines, a driving line result for each driving line and for each of the plurality of demodulation frequencies using the plurality of stored values. 32. Mobile telephone including apparatus for obtaining a plurality of values used to generate a touch image from a touch sensor panel, the apparatus comprising: a plurality of sensing channels, each sensing channel including a charge amplifier configured to receive a signal from a different sense line of the touch sensor panel, a plurality of mixers coupled to an output of the multiplexer, a frequency generator circuit coupled to each of the plurality of mixers for generating a demodulation frequency, and an accumulator coupled to each of the plurality of mixers for generating a value representing an accumulated mixer output; wherein each frequency generator circuit in each sense channel generates a different demodulation frequency, the different demodulation frequencies corresponding to different pacing frequencies applied simultaneously with different phases to the touch sensor panel driver lines. 33. Digital audio player including apparatus for obtaining a plurality of values used to generate a touch image from a touch sensor panel, the digital audio player comprising: a plurality of sensing channels, each sensing channel including a charge amplifier configured to receive a signal from a different sense line of the touch sensor panel, a plurality of mixers coupled to an output of the multiplexer, a frequency generator circuit coupled to each of the plurality of mixers for generating a demodulation frequency, and an accumulator coupled to each of the plurality of mixers for generating a value representing an accumulated mixer output; wherein each frequency generator circuit in each sense channel generates a different demodulation frequency, the different demodulation frequencies corresponding to different pacing frequencies applied simultaneously with different phases to the touch sensor panel driver lines.