The Toshiba TB6504F is another chip from the JVC camcorder. This time it is a PWM chopper type sinusoidal micro step Bipolar stepping motor driver manufactured by Toshiba. It drives one of the motors on the VCR recording/playback assembly. Although this is a 1994 manufactured part, I was able to find a datasheet.
There are absolutely no die markings at all on the chip which is unusual.
The bridge driver outputs are clearly on the right, this is my take on the layout of the chip
Made on a high voltage Bi-CMOS process (In the datasheet), it has two levels of metal and minimum geometry of 5-6 μm. Bipolar transistors and diffusion resistors cover most of the die surface. Two colorful diffusion areas are visible, the pink regions and the light blue areas. I can see no polysilicon layer at all, or any transistors that look like MOSFETs. The bridge drive is covered in two dense metal layers, so it is possible there are MOSFETs there. If used the MOS transistors are likely high voltage devices with a metal gate.
This is the one of the bridge drivers (Imaged with my 20x objective)
As you scan across the device I notice two things:
- the metallization changes with two layers heavily used in the bridge drivers, moderately used in comparator and current control, and only single metal being used in the decoder region. Odd, perhaps they reused an older decoder circuit that was made in a single metal process
- The type of transistor layout used is different in the different regions
Here is an image from the comparator area with two different Bipolar transistor layouts visible, and the two levels of metal