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 TT07, the analog pin voltage is limited to VDDIO/VDDA (usually 3.3 V), so the output voltage will be divided by two. 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. The output voltage stabilizes at ~5.0 V, and the divided output voltage at ~2.5 V. The current draw is about 357 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 a digital 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	0.065	0.130
10	0.236	0.472
50	0.643	1.286
100	1.006	2.012
250	1.524	3.048
500	1.862	3.724
1000	2.091	4.182
2000	2.213	4.426
5000	2.271	4.542
7500	2.276	4.552
10000	2.274	4.548
15000	2.265	4.530
20000	2.254	4.508
40000	2.190	4.380
62000	2.086	4.172
100000	1.768	3.536

* The charge pump voltage is the ua[0] voltage measurement multiplied by 2. This is because the analog pin voltage is limited to 3.3 V, so the charge pump voltage is divided by 2.

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 4.55 V when the input frequency is in the 5-10 MHz range.

269 Dickson Charge Pump