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Logic gates with controllable time delay
| Details |
Inventors: Corcoran, John J.; Poulton, Kenneth D.;
Assignee: Hewlett-Packard Company (Palo Alto, CA)
Primary Examiner: Westin; Edward P.
Assistant Examiner: Sanders; Andrew
Attorney, Agent or Firm:
Apparatus for introduction of a controllable time delay in the transition of a logic device output signal from a first logical level to a second logical level, in response to change of an input signal, or the difference of two input signals from a third logical level to a fourth logical level, delivered to the logic device. In a first embodiment, a limiting amplifier receives an input signal S.sub.in and a threshold signal V.sub.T at its two terminals and forms an amplified difference output signal S.sub.out. A selected voltage level signal V.sub.L and S.sub.out are received at a signum function module and the output signal sgn(S.sub.out -V.sub.L) is formed and issued. The signum output signal is multiplied by a controllable real number m and is added to V.sub.L to form the threshold signal V.sub.T. The desired output signal S.sub.out makes a transition between the first and second logical levels, with a time delay that is controllable by choice of the number m. In a second embodiment, which also uses a signum function, two input signals, S.sub.in,1 and S.sub.in,2, give rise to two output signals, S.sub.out,1 and S.sub.out,2, and the difference signal S.sub.out,1 -S.sub.out,2 makes a transition between two logical levels with a time delay that depends controllably on choice of the number m. |
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DETAILED DESCRIPTION These needs are met by providing a variable threshold voltage logic element.
The threshold voltage is controllably varied, using multiplication means, summation means and Signum function means.
In one embodiment where a single signal controls the change of logical level, a limiting amplifier provides one of two input signals for a Signum function module (sgn(x) = x/abs(x) for x .
noteq.
0, where abs(x) is the absolute value of the number x), with the other input signal being determined by a threshold voltage V.
sub.
L.
Multiplication means is also provided, having two input terminals and an output terminal, for receiving the output signal of the Signum function module at a first input terminal, for receiving a first control input signal representing a numerical value m at a second input terminal, and for forming and issuing the product of these two input signals at the output terminal.
This apparatus includes summation means, having two input terminals and having an output terminal that is connected to the positive (or negative) input terminal of the amplifier, for receiving the multiplication means output signal at a first input terminal, for receiving a second control signal representing a logic threshold value V.
sub.
L at a second input terminal, and for forming and issuing at the output terminal the sum V.
sub.
T of these two input signals.
If an input signal S.
sub.
in is received at the negative input terminal of the amplifier and crosses the threshold level V.
sub.
T at a time t = t.
sub.
O, the output signal issued by the limiting amplifier undergoes a change from one logical level to another logical level at a time t = t.
sub.
O + t.
sub.
d + .
DELTA.
t.
sub.
d, where .
DELTA.
t.
sub.
d is a controllable time delay interval that depends upon m and t.
sub.
d is the time delay of the amplifier for m=0.
A second embodiment for introducing a controllable time delay uses the difference of two independent input signals.
The apparatus includes signal input means having one or more input terminals and two output terminals, for receiving input signals S
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