i A PHYSICAL IMPLEMENTATION WITH CUSTOM LOW POWER ...

Cascaded Inverter Based Delay Element
A series of inverters can be used as a delay element. Such a delay element uses the
propagation delay of the inverters in the chain to obtain the specified delay value. The
propagation delay of an inverter is dependent upon the time to charge and discharge the load
capacitance. The cascaded inverter chain is the simplest delay element topology and is the most
common delay element because of the ease of design. However, such delay elements are
sensitive to environmental variations such as supply voltage and temperature.
The inverter chain shows considerably less supply voltage variation compared to a TG
based delay element [11]. However, the number of inverters in series increases tremendously for
large delay values. With the increase in the number of inverters, the power consumption also
increases. The inverter chain can be used for delays in the range between 1ns to 3ns [16]. Figure
6-3 below shows the schematic of the inverter based delay chain.
NP- Voltage Controlled
Figure 6-3 Cascaded inverter based delay element
A NP-voltage controlled delay element consists of a cascaded inverter pair with a series
connected NMOS and PMOS transistor in the pull-up and pull-down path [15]. The NMOS and
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