269 Dickson Charge Pump :: Quicker, easier and cheaper to make your own chip!

How it works

A 3-stage dickson charge pump. The output voltage is Vout = 4*(VPWR - Vths) = ~5.44 V where VPWR is the digital input voltage (1.8 V), and Vths is the threshold voltage of the LVS NMOS (nominal 0.44 V when width=7, length=8).

How to test

Apply a clock signal of 2 MHz to the clk input. In TT06, the analog pin voltage is limited to 1.8 V, so the output voltage will be divided by 6. You can measure the divided output voltage at the ua[0] (vout_div) pin.

Simulation results

Post layout simulation showing the output voltage x1.vout and the divided output voltage on ta ua[0] pin, with ~16.8 mega ohms load (the internal voltage divider). The output voltage stabilizes at ~5.07 V, and the divided output voltage at ~0.85 V. The current draw is about 355 nA.

output voltage and divided voltage

The following graph shows the input clock, the intermediate voltages at the output of each stage, the output voltage, and the divided voltage as they rise during the first 10 us of operation.

output voltage and intermediate voltages

Silicon measurements

The output voltage on ua[0] was measured with multimeter that has a 7.8MΩ input impedance, at various clock frequencies. The following table summarizes the results:

Input Frequency (KHz)	ua[0] Voltage	Charge Pump Voltage *
0	0.090	0.540
10	0.107	0.642
50	0.171	1.026
100	0.267	1.602
250	0.462	2.772
500	0.604	3.624
1000	0.673	4.038
2000	0.704	4.224
5000	0.716	4.296
7500	0.716	4.296
10000	0.716	4.296
15000	0.714	4.284
20000	0.712	4.272
40000	0.698	4.188
62000	0.676	4.056

* The charge pump voltage is the ua[0] voltage measurement multiplied by 6. This is because the analog pin voltage is limited to 1.8 V, so the output voltage will be divided by 6.

The following graph shows the output voltage as a function of the input frequency:

output voltage vs frequency

Overall, it seems that the charge pump works as expected, with the output voltage peaking at around 4.3 V when the input frequency is in the 5-10 MHz range.

269 Dickson Charge Pump