large drain-source volt drops of the MOSFETs. Frequently, a more complex circuit is used to overcome this problem. One solution is to connect in parallel with the switching MOSFET another MOSFET biased into its linear region. This second MOSFET has a lower drain-source voltage than the switching MOSFET would have on its own (because the switching MOSFET is driven hard on) and consequently the output voltage is increased. The gate of the linear biased MOSFET is connected to the output of the next stage so that it is turned off while the next stage is charging from the previous stage's capacitor. That is, the linear-biased transistor is turned off at the same time as the switching transistor. An ideal 4-stage Dickson multiplier (5× multiplier) with an input of would have an output of . However, a diode-wired MOSFET 4-stage multiplier might only have an output of . Adding parallel MOSFETs in the linear region improves this to around . More complex circuits still can achieve an output much closer to the ideal case. Many other variations and improvements to the basic Dickson circuit exist. Some attempt to reduce the switching threshold voltage such as the Mandal-Sarpeshkar multiplier or the Wu multiplier. Other circuits cancel out the threshold voltage: the Umeda multiplier does it with an externally provided voltage and the Nakamoto multiplier does it with internally generated voltage. The Bergeret multiplier concentrates on maximising power efficiency. Modification for RF power In CMOS integrated circuits clock signals are readily available, or else easily generated. This is not always the case in RF integrated circuits, but often a source of RF power will be available. The standard Dickson multiplier circuit can be modified to meet this requirement by simply grounding the normal input and one of the clock inputs. RF power is injected into the other clock input, which then becomes the circuit input. The RF signal is effectively the clock as well as the source of power. However, since the clock is injected only into every other node the circuit only achieves a stage of multiplication for every second diode-capacitor cell. The other diode-capacitor cells are merely acting as peak detectors and smoothing the ripple without increasing the multiplication. Cross-coupled switched capacitor A voltage multiplier may be formed of a cascade of voltage doublers of the cross-coupled switched capacitor type. This type of circuit is typically used instead of a Dickson