Electronics > Beginners

Could anyone explain the output stage of the print head driver ?.

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sangar:
Hi,

I have been trying to understand the attached circuit since last two days. Though I got something, I am still not sure. There are 64 output channels in which each can output up to 400mA. My assumption is that the feature "16-step grey scale" helps to configure the current of the output channel.
Coming to the attached circuit, it is a channel output stage circuit of 64 channels. The datasheet says that it converts 4-bit parallel input to 16 steps (4-bit) grey scale output. So, I think, at a time, a step (ex.0100) in 16 steps feeds as input to the push-pull configuration. And, the output of the push-pull goes to Transmission gate to switch the COM voltage to the output. Please share your input. Attached the datasheet and image.

capt bullshot:
This is a rather complicated logic to connect the outputs to one of the COM lines. It's kind of staggered, to reduce the amount of current drawn through the COM lines at the same time.
Anyway, the output circuit does nothing but connecting the output to the respective COM lines. The switches are implemented in a similar way as a usual analog switch, so the COM lines can have any voltage within the rated voltage. That might be used for some kind of temperature depending adjustment of the print head, and maybe reversing the driver voltage for whatever reason. I've never dealed with such stuff, so I'm just guessing.
The gray scaling is done by a PWM scheme (varying the turn-on time of the output, in turn varying the amount of energy delivered to the print head. You'll find the PWM scheme at some other page within the data sheet.

In Vacuo Veritas:
Your pictures shows 64 outputs. 4 to the power of 3 == ???

sangar:
Hi,

I don't understand that what you mean by "4 to the power of 3"...I think that each output channel circuit has individual 4 input lines, not a common "4 input lines" for all the output channel. The block diagram in the datasheet looks like not completed. Please correct me if I am wrong.


Thanks,
Muthu

In Vacuo Veritas:
You have 4 inputs, but each one can be -1,0, or 1. 4 to the power of three ... 64.

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