OV7670 Dual Camera Module Application Notes

OV7670 Dual Camera Module Application NotesLast Modified: April 2nd, 2007Document Revision: 1.00OmniVision Technologies, Inc. reserves the right to make changes without further notice to any product herein to improve reliability, function or design. OmniVision does not assume any liability arising out of the application or use of any project, circuit described herein; neither does it convey any license under its patent nor the right of others.This document contains information of a proprietary nature. None of this information shall be divulged to persons other than OmniVision Technologies, Inc. employee authorized by the nature of their duties to receive such information,or individuals or organizations authorized by OmniVision Technologies, Inc.Table of Contents1. OV7670 Dual Camera Solution (3)1.1 OV7670 Dual Camera Design with 2 Connectors (3)1.1.1 Camera Module Reference design (3)1.1.2 Camera phone Reference Design (4)1.2 OV7670 Dual Camera Design with Single Connector (5)1.2.1 Camera Module Reference design (5)1.2.2 Camera Phone Reference Design (6)2 OV7670 Dual Camera Operation (7)2.1 Power Saving Modes (7)2.2 Dual Camera Operation in Power Down Mode (7)2.2.1 Battery On (7)2.2.2 Enter Camera 1 (8)2.2.3 Exit Camera 1 (8)2.2.4 Enter Camera 2 (9)2.2.5 Exit Camera 2 (9)2.3 Dual Camera Operation in Power Off Mode (9)2.3.1 Battery On (9)2.3.2 Enter Camera 1 (10)2.3.3 Exit Camera 1 (11)2.3.4 Enter Camera 2 (11)2.3.5 Exit Camera 2 (12)3. SCCB Bus sharing (13)4. Timing Considerations for Phone PCB Design (13)4.1 Sample with PCLK (14)4.2 Sample with XCLK (14)4.3 Using EMI/ESD Device (15)5. Camera Module Testing (15)5.1 Test Board Modification (15)5.2 Test Procedure (16)5.2.1 Test Camera 1 (16)5.2.2 Test Camera 2 (16)1. OV7670 Dual Camera SolutionDual OV7670 cameras could be used to share single camera port. The PWDN pins of the 2 cameras should be controlled separately by GPIO. The PWDN1 and PWDN2 selects which camera is working and which camera is power down. The outputs (data bus, clock and sync signals) of power down camera could be set to tri-state. So that the outputs of 2 cameras could share same bus.If dual OV7670 cameras are used in camera phone design, please pay attention to following items.a. DVDD should be supplied by external power supply. If DVDD is not supplied by external, OV7670 may not be able to initialize correctly by SCCB initialization.b. PWDN of the two cameras should be controlled separately. PWDN signals are used to select which camera is working and which camera is standby.c. If power off mode is used, the powers of dual cameras should be turned on/turn off simultaneously. If one camera is power on, the other camera is power off, there would be a big current leakage and the power on camera can not work correctly.1.1 OV7670 Dual Camera Design with 2 ConnectorsEach camera has separate connector. In this case, the camera module design is same as single camera solution.1.1.1 Camera Module Reference designNote:AVDD is 2.45V to 2.8V sensor analog power.DVDD is 1.8V sensor digital power.DOVDD is 2.5V to 3.3V sensor digital IO power.Sensor AGND and DGND should be separated and connect to a single point at outside PCB (Don't connect inside module).C1 should close to sensor VREF and AGND.C2 should close to sensor AVDD and AGND.D7:D0 is module YUV and RGB 8bits output.1.1.2 Camera phone Reference DesignIf DOVDD uses different power supply than AVDD, then 3 regulators should be used.If DOVDD uses the same voltage as AVDD, then only 2 regulators are required. R/C filter is used to separate AVDD from DOVDD.Please note thata. The AGND and DGND should be separate inside module and connected together on phone PCB very close to camera module connector.b. Strobe (LED) of the 2 cameras should be separated. The strobe LED should face same direction as the driven camera.c. RESET# pin of camera modules should be controlled by GPIO. It should not be connected to DOVDD as single camera application.1.2 OV7670 Dual Camera Design with Single ConnectorDual cameras share the same FPC and connector. In this case, the camera module design is different than singe camera application.1.2.1 Camera Module Reference designThe PWDN and STRB of the 2 sensors are separated. Other pins such as XCLK, RESET#, SIO_C, SIO_D, D[7:0], PCLK, HREF, VSYNC are connected together to share the same bus.1.2.2 Camera Phone Reference DesignCam era_OnIf DOVDD uses different power supply than AVDD then 3 regulators should be used.Cam era_OnIf DOVDD uses the same voltage as AVDD, then only 2 regulators are required.Note:a. The AGND and DGND should be separate inside module and connected together on phone PCBvery close to camera module connector.b. Strobe (LED) of the 2 cameras should be separated. The strobe LED should face same direction as the driven camera.c. RESET# pin of camera modules should be controlled by GPIO. It should not be connected to DOVDD as single camera application.2 OV7670 Dual Camera Operation2.1 Power Saving ModesThere are 2 kind of power saving modes: power down mode and power off mode. Power down mode means that in power saving mode, all the power supplies to dual camera module are kept. The cameras are set into power down mode by pull high PWDN1 and PWDN2. Power off mode means that in power saving mode, all the power supplies to dual camera module are cut.2.2 Dual Camera Operation in Power Down Mode2.2.1 Battery OnT1: from powers on to PWDN2 pull high, >= 3mst2: from PWDN1 pull high to RESET# pull high, >= 3mst3: from RESET# pull high to SCCB initialization, >= 10mst4: from PWDN1 pull high to PWDN2 pull low, >= 100mst5: from PWDN2 pull low to SCCB initialization, >= 10msStep 1:Reset# is applied to reset both cameras.ResetPDWN1PDWN2SIO_CSIO_DDOVDDDVDDAVDDXCLKStep 2:DOVDD, DVDD and AVDD powers are applied. The 3 powers could be applied simultaneously. If applied separately, the power on sequence should be DOVDD first, DVDD second and AVDD last.Step 3:after 3ms of last power applied, pull high PWDN2. Set camera 2 to power down mode.Step 4:After 3ms, Pull RESET# high.Step 5:After 10ms, initialize camera 1 by SCCB initialization.Step 6:Pull high PWDN1. Set camera 1 to power down mode.Step 7:after 100ms, pull low PWDN2. Set camera 2 to working mode.Step 8:after 10ms, initialize camera 2 by SCCB initialization.Step 9:Pull PWDN2 to high. Both camera are in power down mode.The XCLK should be set to low when both cameras are power down to minimize standby current.2.2.2 Enter Camera 1Step 1:Pull high PWDN2. Pull Low PWDN1. Apply XCLK.Step 2:After 10ms, initialize camera 1 by SCCB initialization.2.2.3 Exit Camera 1Step 1:Pull High PWDN1Step 2:after 100ms, pull low XCLK2.2.4 Enter Camera 2Step 1:Pull high PWDN1, Pull low PWDN2. Apply XCLKStep 2:After 10ms, initialize camera 2 by SCCB initialization.2.2.5 Exit Camera 2Step 1:Pull High PWDN2.Step 2:After 100ms, pull low XCLK.2.3 Dual Camera Operation in Power Off Mode2.3.1 Battery OnNo operation. Both cameras are power off.PWDN1PWDN2SIO_C SIO_DXCLKPWDN1PWDN2SIO_CSIO_DXCLK2.3.2 Enter Camera 1Step 1:Reset# is applied to reset both cameras.Step 2:DOVDD, DVDD and AVDD powers are applied. The 3 powers could be applied simultaneously. If applied separately, the power on sequence should be DOVDD first, DVDD second and AVDD last.Step 3:after 3ms of last power applied, pull high PWDN1. Set camera 1 to power down mode.Step 4:After 3ms, Pull RESET# high.Step 5:After 10ms, initialize camera 2 by SCCB initialization.Step 6:Pull high PWDN2. Set camera 2 to power down mode.Step 7:after 100ms, pull low PWDN1. Set camera 1 to working mode.Step 8:after 10ms, initialize camera 1 by SCCB initialization.ResetPDWN2PDWN1SIO_CSIO_DDOVDDDVDDAVDDXCLKT1: from powers on to PWDN1 pull high, >= 3mst2: from PWDN1 pull high to RESET# pull high, >= 3ms t3: from RESET# pull high to SCCB initialization, >= 10ms t4: from PWDN2 pull high to PWDN1 pull low, >= 100ms t5: from PWDN1 pull low to SCCB initialization, >= 10ms2.3.3 Exit Camera 1Step 1.Pull low XCLK,Step 2.Turn off AVDD, DVDD and DOVDD. The 3 powers could be turned off simultaneously. If turned off separately, AVDD should be turned off first, DVDD second and DOVDD third.Step 3.Pull Low PWDN1, PWDN2 and RESET#2.3.4 Enter Camera 2Step 1:Reset# is applied to reset both cameras.Step 2:DOVDD, DVDD and AVDD powers are applied. The 3 powers could be applied simultaneously. If applied separately, the power on sequence should be DOVDD first, DVDD second and AVDD last.Step 3:after 3ms of last power applied, pull high PWDN2. Set camera 2 to power down mode.Step 4:After 3ms, Pull RESET# high.DOVDDDVDDAVDDXCLK Reset PWDN1PWDN2Step 5:After 10ms, initialize camera 1 by SCCB initialization.Step 6:Pull high PWDN1. Set camera 1 to power down mode.Step 7:after 100ms, pull low PWDN2. Set camera 2 to working mode.Step 8:after 10ms, initialize camera 2 by SCCB initialization.T1:from powers on to PWDN2 pull high, >= 3mst2: from PWDN1 pull high to RESET# pull high, >= 3ms t3: from RESET# pull high to SCCB initialization, >= 10ms t4: from PWDN1 pull high to PWDN2 pull low, >= 100ms t5: from PWDN2 pull low to SCCB initialization, >= 10ms2.3.5 Exit Camera 2Step 1.Pull low XCLK,Step 2.Turn off AVDD, DVDD and DOVDD. The 3 powers could be turned off simultaneously. If turned off separately, AVDD should be turned off first, DVDD second and DOVDD third.Step 3.Reset PDWN1PDWN2SIO_C SIO_D DOVDD DVDDAVDDXCLKPull Low PWDN1, PWDN2 and RESET#3. SCCB Bus sharingThe SCCB bus of OV7670 dual camera solution could share with other I2C device. WhenOV7670 is working, the read/write operation is separated by device address. The device address of OV7670 is 0x42. I2C read/write to address other than the 2 address above will not affect SCCB registers of OV7670.It is recommended to use power down mode when SCCB bus is shared with other device. When OV7670 dual camera module is power down, the SCCB Bus is leave free. The power down of OV7670 doesn't affect the read/write of other I2C device as long as the DVDD of OV7670 is provided by external regulator.It is not recommended to use power off mode when SCCB bus is shared with other device. When OV7670 dual camera module is power off, all the inputs to OV7670 should be pulled low. The inputs include XCLK, RESET#, PWDN1 and PWDN2. If any if the input is not pulled low, the input would leak current to DVDD/DOVDD of OV7670, then the SIO_D and SIO_C may be pulled to unknown state and caused I2C malfunction.4. Timing Considerations for Phone PCB DesignThere are 2 clock signal for OV7670 dual camera module. One is the main clock (input clock) XCLK, the other is the pixel clock (output clock) PCLK. Some backend/baseband chips may use XCLK as pixel sample clock, some backend/baseband chips may use PCLK as pixel sample clock. It is recommended to use PCLK as pixel sample clock.DOVDDDVDDAVDDXCLK Reset#PWDN2PWDN1Let's look at the clock distribution first.So the delay of video data to clock at backend/baseband side is very critical for timing design. If the delay is over the spec. of backend/baseband chip, the backend/baseband chip can not get video data correctly. The incorrect video data may have wrong color, fixed or moving horizontal lines.From the clock distribution diagram above, the delays are:Delay_XCLK = 0Delay_PCLK = PCB_Delay_XCLK + Internal_Delay + PLL_Delay + PCB_Delay_PCLKDelay_Data = PCB_Delay_XCLK + Internal_Delay + PLL_Delay + PCLK_to_Data_Delay + PCB_Delay_Data4.1 Sample with PCLKIf Backend/baseband sample video data with PCLK, the clock data delay isclock_data_delay = Delay_Data – Delay_PCLK= PCLK_to_Data_Delay + PCB_Delay_Data – PCB_Delay_PCLK The clock data delay is not related with PCB delay of XCLK.If PCB is carefully designed so that the wire length of PCLK and Data are same, thenPCB_Delay_Data = PCB_Delay_PCLK, the clock data delay isclock_data_delay = PCLK_to_Data_Delay, not related to PCB layout4.2 Sample with XCLKIf Backend/baseband sample video data with PCLK, the clock data delay isclock_data_delay = Delay_Data – Delay_XCLK= PCB_Delay_XCLK + Internal_Delay + PLL_Delay + PCLK_to_Data_Delay + PCB_Delay_Data The data to clock delay at Baseband/Backend chip are much bigger than sampled with PCLK. And the delay is highly depend on PCB layout. So if XCLK is used to sample video data, it is very likely to have timing issue which would cause incorrect video data.4.3 Using EMI/ESD DeviceIf EMI/ESD device are used in phone design, the PCB delay increase very much. It should be very careful to manipulate the delays to meet timing spec. of backend/baseband chips.1.Try to use PCLK as sample clock of video data.2.XCLK and PCLK should not share ESD/EMI device with other signals. Use dedicateESD/EMI device or R/C filters for XCLK and PCLK. So that the delay on XCLK andPCLK could be adjusted later.3.For dual camera module, use single ESD/EMI device or single R?C filter for XCLK andPCLK to minimize clock delay.4.Carefully layout PCB to keep XCLK wire as short as possible, PCLK wire the same lengthas data lines.5.Minimize the length of FPC of camera module.5. Camera Module TestingIf the dual cameras have separate connector, then usual camera module test procedure forOV7670 could be applied. There is no need to do any change neither on USB 2.0 test board nor camera module testing method.If the dual cameras share same connector, then the USB 2.0 test board should be modified and the testing method should be changed.5.1 Test Board ModificationTo test dual cameras share same connector, the USB 2.0 test board should be modified.Even there are 2 cameras on same FPC, there is only one camera work at the same time. PWDN pins are used to select which camera is work and which camera is power down.It is recommended to use the PWDN control circuit above. It eliminate the possibility that 2 cameras are both set to working mode which may damage the cameras. SW1 is used to select camera. SW2 is used to set both camera to power down mode.SW1SW2Camera SelectionL L Camera 1 power down, camera 2 workingH L Camera 1 working, camera 2 power downAny H Both camera power down5.2 Test Procedure5.2.1 Test Camera 1Un-plug USB 2.0 test board. Insert camera module into connector. Adjust the switches to pull PWDN1 of camera 1 to Low and PWDN2 of Camera 2 to high.Plug in USB 2.0 test board. The camera 2 is in power down mode. The Camera 1 is in active mode. The camera driver initialize OV7670 camera 1. After the LED is on, the camera 1 is ready. Amcap or other application could be opened to test OV7670 camera 1.5.2.2 Test Camera 2Un-plug USB 2.0 test board. Insert camera module into connector. Adjust the switches to pull PWDN1 of camera 1 to High and PWDN2 of Camera 2 to Low.Plug in USB 2.0 test board. The camera 1 is in power down mode. The Camera 2 is in active mode. The camera driver initialize OV7670 camera 2. After the LED is on, the camera 2 is ready. Amcap or other application could be opened to test OV7670 camera 2.Please be careful to PWDN1 and PWDN2 setting. Set PWDN1 and PWDN2 both to low could make camera module damage.。