Browsing by Author "Liang, HC"

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Conductance in a narrow constriction threaded by an impenetrable magnetic flux tube
(1999-10-30)
Liang, HC
;
電子物理學系
;
Department of Electrophysics
The conductance G in a narrow constriction and its dependence on the Fermi energy and on the transverse position of an impenetrable magnetic flux tube is studied. G exhibits oscillatory-like behavior as the transverse position of the tube changes. When there are n propagating subbands, there are n - 1 minimums of G first (except for n = 1) and n minimums later when the Fermi energy grows. Both just below and just above the critical energy exhibiting n propagating subbands, minimums occur at tube,positions mW/n, where W is the transverse width of the constriction and 1 less than or equal to m less than or equal to n - 1.
Critical spacing between emitter and base in InGaP heterojunction bipolar transistors (HBTs)
(2002-10-01)
Huang, CE
;
Lee, CP
;
Liang, HC
;
Huang, RT
;
電子工程學系及電子研究所
In this paper, the influence of the spacing between the emitter and the base on the performance of InGaP heterojunction bipolar transistors (HBT) was experimentally studied. We found that the emitter to base spacing can be reduced to as small as 0.6 mum without causing a significant drop in the current gain. The reduction in emitter-to-base spacing, however, leads to improvement in high-frequency performance and device phase noise. For optimal dc, RF, and low-frequency noise performances, we have determined that a critical spacing of 0.6similar to0.8 mum between the emitter and the base of an InGaP HBT is required.
Effects of incoherent processes on the quantum transport through a finite-range time-modulated potential
(2001-02-01)
Liang, HC
;
Chu, CS
;
電子物理學系
;
Department of Electrophysics
We study the effect of phase randomization on the quantum transport through a finite-range time-modulated potential. The time-modulated potential leads only to coherent inelastic scatterings, and the incoherent processes are described by an S-matrix model proposed originally by Buttiker for the case of time-independent transport. This S-matrix model provides us a systematic way to reinject into the system those electrons that have suffered with incoherent scatterings. The distribution of these reinjected electrons is determined by an effective chemical potential <()over tilde>. For comparison, we study the cases where the incoherent processes occur inside and outside the time-modulated region. The incoherent processes are found to broaden and to smear the structures in the conductance G that are associated with the coherent inelastic scatterings. However, the smearing is more effective when the incoherent processes occur inside the time-modulated potential region.
Flip-flop selection for mixed scan and reset design based on test generation and structure of sequential circuits
(2000-09-01)
Liang, HC
;
Lee, CL
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電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In this paper, a novel mixed selection methodology using flip-flops for scan and reset design is proposed. The method runs test generation fora sequential circuit to obtain reachable states of flip-flops and required states for hard-to-detect faults. The circuit is also explored so as to acquire the structural connection relationship among the flip-flops. By analyzing these three sets of information, the flip-flops can be arranged in an appropriate order for mixed partial scan and reset selection. Instead of selecting the best flip-flop to revise the circuit for the next test generation, we give first priority to independent flip-flops each time in order to reduce the number of iterations. Experimental results show that this method can achieve higher testability with fewer scan/reset flip-flops than can either the scan only or the previous mixed scan/reset methods.
Identifying invalid states for sequential circuit test generation
(1997-09-01)
Liang, HC
;
Lee, CL
;
Chen, JE
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
For sequential circuit test pattern generation incorporating backward justification, we need to justify the values on pip-pops to activate and propagate fault effects, This takes much time when the values to be justified on flip-flops appear to be invalid states, Hence, it is desirable to know invalid states, either dynamically during the justification process or statically before proceeding to test generation. This paper proposes algorithms to identify, before test generation, invalid states for sequential circuits without reset states, The first algorithm explores all valid states from an unknown initial state to search the complete set of invalid states, The second algorithm finds the complete set of invalid states from searching the reachable states for each state, The third algorithm searches the invalid states which are required for test generation to help stop justification early by analyzing dependency among flip-flops to simulate each partial circuit, Experimental results on ISCAS benchmark circuits show that the algorithms can identify invalid states in short time. The obtained invalid states were also used in test generation, and it was shown that they improved test generation significantly in test generation time, fault coverage, and detection efficiency, especially for larger circuits and for those that were difficult to generate.
Identifying invalid states for sequential circuit test generation
(1997-09-01)
Liang, HC
;
Lee, CL
;
Chen, JE
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
For sequential circuit test pattern generation incorporating backward justification, we need to justify the values on pip-pops to activate and propagate fault effects, This takes much time when the values to be justified on flip-flops appear to be invalid states, Hence, it is desirable to know invalid states, either dynamically during the justification process or statically before proceeding to test generation. This paper proposes algorithms to identify, before test generation, invalid states for sequential circuits without reset states, The first algorithm explores all valid states from an unknown initial state to search the complete set of invalid states, The second algorithm finds the complete set of invalid states from searching the reachable states for each state, The third algorithm searches the invalid states which are required for test generation to help stop justification early by analyzing dependency among flip-flops to simulate each partial circuit, Experimental results on ISCAS benchmark circuits show that the algorithms can identify invalid states in short time. The obtained invalid states were also used in test generation, and it was shown that they improved test generation significantly in test generation time, fault coverage, and detection efficiency, especially for larger circuits and for those that were difficult to generate.
Invalid state identification for sequential circuit test generation
(1996)
Liang, HC
;
Lee, CL
;
Chen, JE
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Quantum transport in a double-barrier structure in the presence of a finite-range time-modulated potential
(1999-08-01)
Chu, CS
;
Liang, HC
;
電子物理學系
;
Department of Electrophysics
We have studied the quantum transport phenomena in a double-barrier structure acted upon by a finite-range time-modulated potential. Inter-side-band mhw transitions are made possible by the finiteness in the range of the oscillating field. For the case when the barrier width is small, such that the resonance state in between the barriers is too broadened, the de conductance G exhibits peaks or dip structures when the chemical potential mu is at mhw above the band bottom. For the case when the barrier width is large, such that the resonance state in between the barriers is well defined, the above feature is masked by resonant tunneling processes when mu is at energies mhw away from the resonant energy E-b. In both cases, the dips or peaks in G are due to the temporary trapping of the transmitting electrons by the quasi-bound states. Furthermore, for the latter case, we also obtain the quenching of the resonant transmission found by Wagner, but with a small quantitative modification. Our calculation is nonperturbative which is valid for arbitrary potential strength and frequency. The form of the time-modulated potential is expected to be realized in a gate-induced potential configuration.
Quantum transport through a quantum well in the presence of a finite-range time-modulated potential
(1999-10-01)
Chu, CS
;
Liang, HC
;
電子物理學系
;
Department of Electrophysics
We have studied the transport of electrons through a quantum well within which a time-modulated potential of amplitude V-2, range a, and frequency w is applied. Our results show that, as the chemical potential mu increases, the de conductance G exhibits Fano-structures when mu is at m (h) over bar w above the bound state energy in the well. As V-2 increases, the Fano-structures are broadened, and higher m (h) over bar w processes emerge. These features are identified as the formation of quasi-bound states. For a fixed but large potential strength V-1 = aV(2), the Fano-structures are broadened and are shifted toward lower electron energies, as a decreases. The dependence of the Fano-structure to the location of the time-modulated potential is also studied.
Transmission coefficients in a narrow constriction threaded by two impenetrable magnetic flux tubes
(2000-02-10)
Liang, HC
;
電子物理學系
;
Department of Electrophysics
The transmission coefficients in a narrow constriction and their dependence on the Fermi energy and on the transverse positions of two impenetrable magnetic Bur tubes is studied. An overlapping integral L-mn can qualitatively represent the strength of interaction between incoming subband rn and outgoing subband n. The conductance G and its components exhibit oscillatory-like behavior as the transverse positions of the tubes change.