TWI694361B - Touch display panel and driving method for same - Google Patents

Abstract

The invention provides a touch display panel includes a substrate, a plurality of scanning lines and a plurality of data lines formed on the substrate, the scanning lines and the data lines cross each other to define a plurality of sub-pixel units, and a plurality of first thin film transistors (TFTs) and a plurality of second TFTs formed on the substrate. The touch display panel also includes a plurality of touch scan lines parallel to and adjacent to the scanning line and a plurality of touch lines parallel to the data line. The touch scan lines and the touch lines intersect each other to define a plurality of sensing units. The touch display panel provided by the invention not only realizes the display function and touch sensing function, but also realizes the fingerprint sensing function. The invention also provides a driving method of the touch display panel.

Description

Touch display panel and its driving method

The invention relates to the field of touch display, in particular to a touch display panel with fingerprint recognition function and a driving method thereof.

As an information input tool, the touch display panel is widely used in various display products with information interaction functions such as design, tablet computers, and information inquiry machines in public halls. However, the display area of most existing devices can provide both display and touch functions, but it cannot provide fingerprint recognition functions. Instead, a fingerprint recognition device is provided in the non-display area to realize the fingerprint recognition function.

In view of this, it is necessary to provide a touch display panel whose display area can provide a fingerprint recognition function when providing display and touch functions.

A substrate; a plurality of scanning lines and a plurality of data lines formed on the substrate, the plurality of scanning lines and the data lines crossing each other to define a plurality of sub-pixel units; a plurality of first thin film transistors (TFTs) formed on the substrate And a plurality of second TFTs; a common electrode layer formed on the plurality of first TFTs and the plurality of second TFTs, which includes a plurality of spaced common electrodes; a plurality of pixel electrodes formed on the common electrode, each A pixel electrode is correspondingly arranged in a sub-pixel unit; The touch display panel further includes a plurality of touch scanning lines parallel to and adjacent to the scanning lines, and a plurality of touch touching lines parallel to the data lines. The plurality of touch scanning lines and the touch lines cross each other to define a plurality of sensing units , The gate of the second TFT is electrically connected to a touch scan line, the source is connected to a touch line, the drain is connected to a common electrode, and the data line and the touch line are arranged in the same layer, the The data line and the touch scanning line are arranged on the same layer as the scanning line.

Another touch display panel provided by the present invention includes: a substrate; a plurality of scan lines and a plurality of data lines formed on the substrate, and the plurality of scan lines and the plurality of data lines cross each other to define a plurality of sub-pixel units; A plurality of first thin film transistors (TFT) and a plurality of second TFTs formed on the substrate; a plurality of spaced common electrodes formed on the plurality of first TFTs and the plurality of second TFTs; formed on the substrate A plurality of pixel electrodes on the plurality of common electrodes, each pixel electrode is correspondingly arranged in a sub-pixel unit, and each sub-pixel unit is provided with a first TFT, and the first TFT is used to control the picture The conduction of the element electrode and the data line; the plural touch scan lines parallel and adjacent to the scan line; the plural touch lines parallel to the data line, the plural touch lines and the plural touch scan lines cross each other to define a plural number In the sensing unit, the gate of the second TFT is electrically connected to a touch scan line, the source is connected to a touch line, and the drain is connected to a common electrode; and a driving circuit is connected to the data line and the touch Line and the touch scan line are electrically connected. During the display period, the driving circuit applies a common voltage signal to the plurality of common electrodes, and applies a display signal to the plurality of pixel electrodes for image display; during the touch period, The driving circuit applies a touch driving signal to the plurality of common electrodes for touch sensing; during the fingerprint sensing period, the driving circuit applies a fingerprint sensing signal to the plurality of common electrodes for fingerprint sensing.

The invention also provides a driving method of the above touch display panel, which includes: within each frame of an odd-numbered frame, an alternating display period and a touch period are included, and during the display period, a common voltage signal is applied to the plurality of common electrodes, And display signals are applied to the plurality of pixel electrodes In order to achieve image display; during the touch period, the plurality of common electrodes are applied with a touch drive signal to realize touch sensing in each frame of the even-numbered frames, including the fingerprint sensing period, and within the fingerprint sensing period, A fingerprint sensing signal is applied to the common electrode to realize fingerprint sensing; the odd-numbered frames and the even-numbered frames alternate.

In the touch display panel provided by the present invention, in addition to the display function and the touch sensing function, the display area can also realize the fingerprint sensing function. For electronic devices including the touch panel, the fingerprint recognition function can be implemented directly in the display area without the need for a separate fingerprint sensing device, which further improves the integration of the electronic device and reduces the volume and weight of the electronic device.

100: touch panel

10: substrate

11: First TFT

12: Second TFT

111, 121: gate

112, 122: source

113, 123: Jiji

20: Sensing unit

21.TL, TL-1~TL-N: touch line

22. TGL, TGL-1~TGL-N: touch scanning line

23.GL, GL-1~GL-N: scanning line

24. DL, DL-1~DL-N: data cable

31: Common electrode

33: pixel electrode

40: Drive circuit

41: Sub-pixel unit

42: Pixel unit

M1: the first metal layer

M2: second metal layer

M3: third metal layer

101: the first insulating layer

102: second insulating layer

103: third insulating layer

104: fourth insulating layer

FIG. 1 is a schematic diagram of a touch panel.

FIG. 2 is an enlarged schematic view of part II of FIG. 1.

FIG. 3 is a cross-sectional view of the first embodiment of the touch panel of FIG. 2 along the section line III-III.

FIG. 4 is a cross-sectional view of the first embodiment of the touch panel of FIG. 2 along the cross-sectional line IV-IV.

FIG. 5 is a cross-sectional view of the second embodiment of the touch panel of FIG. 2 along the section line III-III.

6 is a cross-sectional view of the second embodiment of the touch panel of FIG. 2 along the cross-sectional line IV-IV.

7 is a schematic diagram of a touch panel.

8 is a schematic diagram of the cycle of the touch panel in different periods.

9 is a circuit diagram of a period corresponding to the display stage of the touch panel in FIG. 4.

FIG. 10 is a circuit diagram of a time period of the touch stage of the touch panel corresponding to FIG. 4.

FIG. 11 is a circuit diagram of the time period of the fingerprint sensing stage of the panel of FIG. 4.

The specific embodiments of the present invention will be described in detail below with reference to the drawings.

Referring to FIG. 1, the touch panel 100 includes a substrate 10, and a plurality of sub-pixel units 41 defined on the substrate 10 are arranged in a matrix. The three sub-pixel units 41 adjacent in the first direction D1 shown in FIG. 1 define one pixel unit 42.

As shown in FIG. 2, the touch panel 100 includes a plurality of scan lines 23 extending in a first direction D1 and a plurality of data lines 24 extending in a second direction D2, where the second direction D2 is perpendicular to the first direction D1. In this embodiment, the second direction D2 is orthogonal to the first direction D1. Each adjacent two scanning lines 23 and each adjacent two data lines 24 cross each other to define a sub-pixel unit 41.

As shown in FIG. 2, the touch panel 100 further includes plural first TFTs 11 and plural second TFTs 12 formed on the substrate 10, and plural common electrodes 31 formed on the plural first TFTs 11 and plural second TFTs 12.

As shown in FIG. 2, the touch panel 100 further includes a plurality of touch scanning lines 22 parallel to and adjacent to the scanning lines 23, a plurality of touch lines 21 parallel to the data lines 24, a plurality of touch scanning lines 22 and a plurality of touches The lines 21 cross each other to define the complex sensing unit 20.

As shown in FIG. 2, each touch scan line 22 and one scan line 23 are adjacent and appear in pairs, and each pair of touch scan lines 22 and scan line 23 corresponds to a row of sub-pixel units 41 (along FIG. 2). As shown in the first direction D1), the number of scanning lines 23 and touch scanning lines 22 in the touch panel 100 is equal. Each data line 24 corresponds to a row of sub-pixel units 41 (along the second direction D2 shown in FIG. 2), and each touch line 21 corresponds to a column of pixel units 42 (along the second direction D2 shown in FIG. 2). Then, the number of touch lines 21 in the touch panel 100 is less than the number of data lines 24.

As shown in FIG. 2, the touch panel 100 further includes a plurality of pixel electrodes 33. In this embodiment, each common electrode 31 corresponds to three adjacent sub-pixel units 41 (one pixel unit 42), and each pixel electrode 33 corresponds to one sub-pixel unit 41, that is, each common electrode 31 corresponds to three个Pixel electrode 33.

As shown in FIG. 1, the touch panel 100 further includes a driving circuit 40. The driving circuit 40 is electrically connected to the data line 24 and the touch line 21. The driving circuit 40 is used to apply a common voltage signal to the plurality of common electrodes 31 during the display period and apply a display signal to the plurality of pixel electrodes 33 to achieve image display. The driving circuit 40 is electrically connected to the touch line 21 and the touch scan line 22. The driving circuit 40 is used for touch The segment applies a touch driving signal to the plurality of common electrodes 31 to realize touch sensing; and during the fingerprint sensing period, the driving circuit 40 applies a fingerprint sensing signal to the common electrode 31 to achieve fingerprint sensing.

As shown in FIG. 2, each sensing unit 20 is corresponding to a common electrode 31, and each sensing unit 20 is correspondingly provided with a second TFT 12. The gate electrode 121 of each second TFT 12 is electrically connected to the touch scan line 22, the source electrode 122 of each second TFT 12 is electrically connected to the touch line 21, and the drain electrode 123 of each second TFT 12 is connected to a common electrode 31 Electrical connection. In this embodiment, each sensing unit 20 is rectangular, and its side length is less than 100 μm. Therefore, the sensing unit 20 can separately detect protrusions and depressions on the fingerprint to realize fingerprint sensing.

In this embodiment, the gate 111 of each first TFT 11 is electrically connected to the scan line 23, the source 112 of each first TFT 11 is electrically connected to the data line 24, and the drain 113 of each first TFT 11 is connected to one The pixel electrode 33 is electrically connected.

Please refer to Figure 2, Figure 3 and Figure 4 together. The touch panel 100 includes a plurality of metal layers disposed on the substrate 10. According to the distance from the substrate 10 and the order of stacking on the substrate 10, the scan line 23 and the touch scan line 22 are located in the metal layer to define the first metal layer M1, the data line 24 and the metal layer where the touch line 21 is located define the second metal layer M2. An insulating layer is provided between different metal layers to electrically insulate.

As shown in FIG. 3, in the first embodiment, a first metal layer M1 is provided on the substrate 10, and the scan line 23 and the touch scan line 22 are patterned by the first metal layer M1.

As shown in FIGS. 3 and 4, the surface of the substrate 10 provided with the first metal layer M1 is further provided with a first insulating layer 101. As shown in FIG. 3, the first insulating layer 101 completely covers the scan line 23 and the touch scan line 22. As shown in FIG. 4, a second metal layer M2 is provided on the side of the first insulating layer 101 away from the substrate 10. The data line 24 and the touch line 21 are patterned by the second metal layer M2. A first insulating layer 101 is provided between the first metal layer M1 and the second metal layer M2 to electrically insulate the two.

The substrate 10 includes a first TFT 11 and a second TFT 12 (not shown in FIGS. 3-4, only shown in FIG. 2). The insulating layer provided between the different metal layers and the common electrode 31 and the pixel electrode 33 is provided with vias (not shown), that is, the pixel electrode 33, the first TFT 11 and the scan line 23 located on the first metal layer M1 2. The data line 24 located in the second metal layer M2 can be electrically connected by providing vias in the first insulating layer 101, the second insulating layer 102, and the third insulating layer 103. The common electrode 31, the second TFT 12 and the The touch scan lines 22 of the metal layer M1 and the touch lines 21 of the second metal layer M2 can also be electrically connected by providing vias in the insulating layer.

Please refer to FIG. 2, FIG. 5 and FIG. 6 together, which are cross-sectional views of another modified embodiment. In this embodiment, the metal layer where the scan line 23 and the touch scan line 22 define the first metal layer M1, the metal layer where the data line 24 locates define the second metal layer M2, and the metal layer where the touch line 21 locates defines the third metal layer M3 . That is, the data line 24 and the touch line 21 are located in different layers, and are formed by patterning different metal layers.

As shown in FIGS. 5 and 6, the surface of the substrate 10 provided with the first metal layer M1 is also provided with a first insulating layer 101. As shown in FIG. 5, the first insulating layer 101 completely covers the scanning line 23 and the touch scanning line twenty two. As shown in FIG. 6, the side of the first insulating layer 101 away from the substrate 10 is provided with a second metal layer M2. The data line 24 is patterned by the second metal layer M2. A first insulating layer 101 is provided between the first metal layer M1 and the second metal layer M2 to electrically insulate the two.

As shown in FIGS. 5 and 6, the second insulating layer 102 is stacked on the side of the first insulating layer 101 away from the substrate 10. As shown in FIG. 6, the second insulating layer 102 completely covers the data line 24. As shown in FIG. 5, a third metal layer M3 is provided on the side of the second insulating layer 102 away from the substrate 10. The touch line 21 is patterned by the third metal layer M3. A third insulating layer 103 is stacked on the side of the second insulating layer 102 away from the substrate 10, and the third insulating layer 103 completely covers the touch line 21. A plurality of common electrodes 31 are provided on the side of the third insulating layer 103 away from the substrate 10. A fourth insulating layer 104 is laminated on the side of the third insulating layer 103 away from the substrate 10, and the fourth insulating layer 104 completely covers the common electrode 31. The fourth insulating layer 104 is provided with a plurality of pixel electrodes 33 arranged at intervals on the side away from the substrate 10. A fourth insulating layer 104 is provided between the common electrode 31 and the pixel electrode 33 to electrically insulate the two.

The first insulating layer 101, the second insulating layer 102, and the third insulating layer 103 are provided with via holes (not shown). The touch scanning line 22, the scanning line 23, the second TFT 12 and the common electrode 31 can be electrically connected through a via in the insulating layer. That is, the second TFT 12 and the touch scan line 22 located in the first metal layer M1 and the touch line 21 in the third metal layer M3 can be electrically connected through the through hole of the insulating layer.

Please refer to Figures 7-10 together. The display resolution of the touch panel shown in FIG. 7 is 720RGB*1280.

The driving of the touch panel 100 shown in FIG. 7 is divided into plural frames, and the plural frames include plural odd frames and plural even frames. As shown in FIG. 8, the driving of the touch panel 100 includes a display period and touch Time period and fingerprint sensing period, where the display period (DP) and touch period (TP) share one frame (odd frame), and the fingerprint sensing period (FP) needs to be time-shared with the display period and touch period in another frame ( Even frames). The display period and the touch period alternate in the same odd-numbered frame. For example, assuming that in every odd-numbered frame, the number n including the display period and the touched period is 16, then in every odd-numbered frame, every two displays There is a touch period between periods. The even frames including fingerprint sensing alternate with the odd frames where the display period and the touch period are located. For example, the first frame includes the display period and the touch period, that is, the touch panel performs display and touch sensing at 100 minutes in the first frame, and the second frame is the fingerprint sensing period, that is, the touch in the second frame The control panel 100 performs fingerprint sensing, the third frame includes a display period and a touch period, the fourth frame is a fingerprint sensing period, and so on. The touch panel can complete display, touch sensing and fingerprint sensing.

As shown in FIG. 9, when the display scan frequency is 60 Hz, one frame includes alternating n display periods (DP) and n touch periods (TP). In the first display period (DP1), the scan signals from line 1 to line 80 (GL-1~GL-80) are applied one by one, and all data lines DL are applied with square wave signals to control the data line 24 The conduction with the pixel electrode 33 causes the display signal to be applied to the pixel electrode 33; at the same time, the scan signals from the first to the 80th (TGL-1~TGL-80) of the touch scan line are applied one by one to control the common electrode 31 At the same time as the touch line 21 is turned on, at the same time, all touch lines TL are applied with a display drive signal (common voltage signal), so that the common electrode 31 is applied with a display drive signal (common voltage signal). That is, all the touch lines TL maintain a common voltage, and the data lines 1 to 2160 (DL-1 to DL-2160) give the pixel electrode 33 a display signal. In the second display period (DP2), the 81st to 160th scanning lines (GL-81~GL-160) and the 81st to 160th scanning touch lines (TGL-81~TGL-160) are both Scan signals are applied one by one, the touch lines 1 to 720 (TL-1~TL-720) maintain a low level signal (common voltage signal), and the data lines 1 to 2160 (DL-1~DL -2160) The pixel electrode 33 is given a display signal. By analogy, the remaining signal patterns from the third display period (DP3) to the nth display period (DPn) can be used to complete the full screen scan. Each complete screen scan can get a complete display image.

Referring to FIG. 10, in the first touch period (TP1), a plurality of adjacent common electrodes 31 serve as a touch electrode, and provide touch sensing signals to the touch electrodes via the touch wires 21, and The electrodes perform self-capacitance detection to achieve touch sensing.

The display scan frequency is 60Hz and the touch scan frequency is 120Hz. During the first touch period (TP1), the image display is not updated at this time. All scan lines from 1 to N (GL -1~GL-N) Low level signal is applied, and all data lines DL-1~DL-N are grounded, so that the pixel electrode 33 is floating; touch scanning lines 1 to 40 (TGL-1 ~TGL-40) Scan signals are applied at the same time, all the touch lines 1 to 720 (GL-1~GL-720) are applied with a touch drive signal, which is applied to the common electrode 31 of the 1-40th line Touch drive signal; then touch scan lines 1 to 40 (TGL1~GL40) stop applying scan signals, and touch scan lines 41 to 80 (TGL-41~TGL-80) are simultaneously Applying the scanning signal, all the touch lines 21 to 720 (TL-21~TL-720) are given touch sensing signals, so that the touch sensing signals are applied to the common electrodes 31 on the 41-80th row, And so on, until the common electrodes 31 of lines 121-160 are completed, a touch sensing signal is applied.

In the second touch period (TP2), it is necessary to complete the 161-320 rows of the common electrode 31 to be applied with a touch driving signal. After the last line in the 2/n touch period (TP2/n) is completed, the common electrode 31 is applied with a touch drive signal and starts from the common electrode 31 in the first line, thus scanning under each frame of image (60 Hz) Full screen 2 times is 120Hz touch scanning frequency.

Referring to FIG. 11, in the fingerprint sensing stage, each common electrode 31 serves as a fingerprint sensing electrode, and the driving circuit 40 provides a fingerprint sensing signal to the common electrode 31 through the touch line 21 and performs self-capacitance detection on the common electrode 31 To achieve fingerprint sensing.

When performing fingerprint sensing, a complete frame image is required. At this time, the image display does not update the display image. All scan lines GL are applied with a low-level signal, and all data lines DL are grounded to make the pixel electrode 33 floating; all touch scanning lines TGL are applied with scan signals one by one, all touch lines TL are applied with fingerprint sensing signals, and fingerprint sensing signals are applied from the common electrode 31 in the first row, and so on until The common electrode 31 having completed 1280 lines is applied with a fingerprint sensing signal. After scanning, you can get a full-screen fingerprint collection image.

In addition, the above-mentioned display resolution, touch resolution, display period and number N of touch periods can be adjusted according to different applications. The above are only examples for explaining the status of different lines in different modes.

The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. The up, down, left, and right directions appearing in the illustration are only for easy understanding, although the present invention is referred to with reference to the preferred embodiments. After detailed description, those with ordinary knowledge in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention.

11: First TFT

12: Second TFT

111, 121: gate

112, 122: source

113, 123: Jiji

20: Sensing unit

21: Touch line

22: Touch scan line

23: Scan line

24: data line

31: Common electrode

33: pixel electrode

41: Sub-pixel unit

42: Pixel unit

Claims (11)

A touch display panel, comprising: a substrate; a plurality of scanning lines and a plurality of data lines formed on the substrate, the plurality of scanning lines and the plurality of data lines crossing each other to define a plurality of sub-pixel units; formed in the Plural first thin film transistors (TFT) and plural second TFTs on the substrate; plural common electrodes formed on the plural first TFTs and the plural second TFTs spaced apart; formed on the plural common electrodes A plurality of pixel electrodes, each pixel electrode is correspondingly disposed in a sub-pixel unit; the improvement is that the touch display panel further includes a plurality of parallel touch scan lines parallel to the scan lines and adjacent to the data lines Parallel plural touch lines, the plural touch scanning lines and the touch lines cross each other to define a plural sensing unit, the gate of the second TFT is electrically connected to a touch scanning line, and the source is connected to a touch line , The drain is connected to a common electrode; the driving of the touch display panel includes a display period, a touch period, and a fingerprint sensing period. During the display period, a common voltage signal is applied to the plurality of common electrodes to achieve image display; During the control period, a touch driving signal is applied to the plurality of common electrodes to implement touch sensing; during the fingerprint sensing period, a fingerprint sensing signal is applied to the common electrodes to implement fingerprint sensing. The touch display panel according to claim 1, wherein the driving of the touch panel is divided into a complex odd frame and a complex even frame, wherein each odd frame includes an alternating display period and a touch period, and each even frame includes During the fingerprint sensing period, the odd-numbered frames and the even-numbered frames are alternately performed. The touch display panel according to claim 1, wherein the plurality of touch scan lines and the plurality of scan lines are provided in the same layer; the plurality of touch lines and the plurality of data lines are provided in the same layer, and The plurality of touch scan lines and the plurality of touch lines are disposed on different layers. The touch display panel according to claim 1, wherein the plurality of touch scan lines and the plurality of scan lines are provided in the same layer; the plurality of touch scan lines and the plurality of touch lines are provided in different layers The complex data lines and the complex touch scan lines and the touch lines are arranged in different layers. The touch display panel according to claim 1, wherein the sub-pixel units are arranged in a matrix into a plurality of rows and a plurality of columns, and at least three adjacent sub-pixel units in the same row define a pixel unit, each touch The control scan lines are adjacent to and paired with a scan line, each pair of touch scan lines corresponds to a row of sub-pixel unit settings; each touch line corresponds to a row of pixel unit settings, and each data line corresponds to a row of sub-pixel units Pixel unit settings. The touch display panel according to claim 5, wherein each pixel unit is correspondingly provided with a common electrode and a second TFT. The touch display panel according to claim 1, wherein each sensing unit is rectangular, and its side length is less than 100 μm. The touch display panel according to any one of claims 1 to 7, wherein each sub-pixel unit is provided with a first TFT, the gate of each first TFT is electrically connected to a scan line, and the source A data line is connected, a drain electrode is connected to a pixel electrode, and the conduction between the pixel electrode and the data line is controlled by the first TFT. The touch display panel according to claim 1, wherein in the fingerprint sensing period, a low-level signal is applied to the scan line, the data line is grounded, and the pixel electrode is floated; the touch scan Scanning signals are applied to the lines one by one, and fingerprint sensing signals are applied to the touch lines to complete fingerprint sensing. A touch display panel, the improvement of which includes: a substrate; a plurality of scanning lines and a plurality of data lines formed on the substrate, the plurality of scanning lines and the plurality of data lines crossing each other to define a plurality of sub-pixel units; forming Plural first thin film transistors (TFT) and plural second TFTs on the substrate; plural common electrodes formed at intervals on the plural first TFTs and the plural second TFTs; formed on the plural A plurality of pixel electrodes on the common electrode, each pixel electrode is correspondingly arranged in a sub-pixel unit, and each sub-pixel unit is provided with a first TFT, and the pixel is controlled by the first TFT Conduction of electrodes and data lines; a plurality of adjacent touch scan lines parallel to and adjacent to the scan lines; A plurality of touch lines parallel to the data line, the plurality of touch lines and the plurality of touch scan lines cross each other to define a plurality of sensing units, the gate of the second TFT is electrically connected to a touch scan line, the source The pole is connected to a touch line, the drain electrode is connected to a common electrode; and the drive circuit is electrically connected to the data line, the touch line, and the touch scan line. During the display period, the drive circuit Applying a common voltage signal to the common electrode and applying a display signal to the complex pixel electrodes for image display; during the touch period, the drive circuit applies a touch drive signal to the complex common electrodes for touch sensing; During the fingerprint sensing period, the driving circuit applies a fingerprint sensing signal to the plurality of common electrodes to perform fingerprint sensing. A driving method for a touch display panel according to any one of claims 1 to 9, comprising: each frame of an odd-numbered frame includes an alternating display period and a touch period. During the display period, the plural numbers are common A common voltage signal is applied to the electrodes, and a display signal is applied to the plurality of pixel electrodes to achieve image display; during a touch period, a touch drive signal is applied to the plurality of common electrodes to implement touch sensing; even frames Each frame includes a fingerprint sensing period. During the fingerprint sensing period, a fingerprint sensing signal is applied to the common electrode to realize fingerprint sensing; the odd-numbered frames and the even-numbered frames alternate.

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