TAILIEUCHUNG - Advances in Analog Circuits Part 7

Tham khảo tài liệu 'advances in analog circuits part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Analog Design Issues for Mixed-Signal CMOS Integrated Circuits 169 7 8 9 f 0 the term ỗ f H f 12 in 6 can be replaced with ỗ f H2 0 ỗ f Q2 where Q is the charge transferred during the complete switching of a single logic gate r TO Q H 0 h t dt. TO Therefore the power spectral density Si f of the stochastic process I t is Si f A2Q20 f A . H f 2 and the normalized power Pi of the switching current I t is Pi i 7 Si f df A2Q2 A TO IH f 12df. TO TO In 9 the term A2 Q2 is the dc component of the digital switching power AQ is the average value of the current drawn from the supply voltage while the term A I TOTO IH f I2df is the ac component of the switching power. The rightmost term in 9 can be simplified by using Parseval s theorem thus obtaining PI A2Q2 A l h2 t dt. 10 TO For any impulse response h t the normalized power Pi can be written as Pi A2 Q2 aA Q2 11 tp where a is a pulse shape factor which depends on the single current pulse waveform in time domain and tp is the switching time of logic gates Boselli et al. 2010 . Current pulses with different duration amplitude and time density Although equations 4 to 11 were derived starting from restrictive assumptions the theory can be extended to digital systems made of logic cells with different switching time different switching currents and switching activity variable over time. Let us start considering different switching times. For simplicity let us assume that the combinational circuit is made of two types of logic cells labeled A and B . In more detail gates of type A are characterized by the digital switching current iA t which can be described as a shot noise with time density A A and impulse response h-A t and gates of type B are characterized by the digital switching current iB t with time density Ab and impulse response h-B t . The total current drawn by the whole circuit is i t ÌA t ÌB t 12 which is the sum of two shot noise processes. The amplitude distribution f i of the total current i t is f i fA i fB

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