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USB Bridge

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angusgbishop edited this page Feb 25, 2021 · 5 revisions

Introduction

As no sensor outputs directly to USB (That I know of) some sort of bridge is needed between the sensor and USB.

The constraints are low-cost + small-size. The solutions I've considered are below;

Dedicated IC's

  • FTDI FT602Q
  • Cypress CYUSB306X <- Not used due to difficulty laying out 2 BGA IC's on a small 4 layer board without blind/buried vias.
  • Omnivision OV580 <- Not available in low volumes.

Microcontrollers

  • Espressif ESP32(+-S2) <- Maximum pixel clock of 40Mhz - Too low for useful integration with HD sensors.
  • STMicroelectronics STM32H723VET6
  • NXP IMXRT1062 <- More expensive than the STM & BGA issues as per CYUSB306X

FT602

The FT602 is a neat little IC that does a fairly good job of bridging parallel video data into USB. However it has some fairly large issues for this application, seemingly stemming from the assumption that this will be used in conjunction with an FPGA.

  • Pixel clock is driven at one of two fixed frequencies, 66Mhz or 100Mhz.
  • Does not master I2C bus
  • Complex system of frame start signalling.

STMicroelectronics STM32H723VET6

The STM32H723VET6 is a very powerful DSP microcontroller. Available in an LQFP-100 package, it can sit neatly underneath the image sensor.

Although this device is much more flexible it does have downsides;

  • Power consumption is potentially much higher (2.5W vs ~1W)
  • Full software stack must be developed.
  • Integrated USB PHY only capable of running at 12MB/s, insufficent data rate without compression or an external High speed PHY

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