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Regulated charge pump design

I am working with an IC that uses a partially intergrated regulated charge pump. The circuit looks like this:

![Charge pump circuit](https://electrical.codidact.com/uploads/msfz1k5urxw1dma9bpr4731q8aqn)

It behaves like a voltage doubler. However, when looking at other regulated charge pumps I am coming across much simpler designs such as this on for example:

![Other pump circuits](https://electrical.codidact.com/uploads/ba0oca25442otyc1cf7cv0eeboqm)

I understand the wokring of a single-stage charge pump and the fact that they can be chained together. However, the circuit from the first diagram confuses me as it looks like nothing I could find online.

My questions are:

 - Why are C2 and C3 connected across D2 and D3?
 - What is the purpose of C1?
 - What type of charge pump is this?