US 4,728,821 AGranted

Source follower current mode logic cells

AssigneeDigital Equipment Corporation

InventorsJ. Leon Yang, Joseph P. Zeh

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Abstract

A source follower current steering logic circuit useful in, for example, fabricating digital integrated logic circuits using gallium arsenide and current mode logic switches. The circuit includes an input logic network which includes level shifting networks to generate output signals having assertion levels of different voltage levels and a reference voltage logic network having a similar level shifting network for generating reference voltages relative to the voltage levels of the assertion levels of the output signals from the input logic network. A logic tree includes current mode logic switches for receiving the output signals from the input logic network and the reference voltage generating network to perform selected logic operations the output signals. The output signals are taken from the logic tree. A top load clamps the output signals to selected voltage levels.

Claims13

Dependent claims

A source follower current steering logic circuit for performing a logic operation on a plurality of input signals comprising:

A. first and second input branches each including:
(i) input means for receiving an input signal and for generating a signal in response thereto;
(ii) signal generating means connected to said input means for receiving the signal therefrom and for generating an output signal having a selected voltage level in response thereto, said signal generating means of both said first and second input branches having a corresponding predetermined number of level shifting means each having an output connected serially between a power supply means and said input means, the output signal from signal generating means of one input branch being taken from the output of a different level shifting means than the output of the signal generating means of the other input branch so that output signals from the first and second input branches have different voltage levels;
B. reference branch means also having a plurality of serially-connected level shifting means, each having an output connected to a power supply means, the number of level shifting means in said reference branch means corresponding to the number of level shifting means in said signal generating means in each of said input branches, the reference branch means generating reference voltage signals from the outputs of level shifting means corresponding to the level shifting means in said signal generating means of each of said first and second input branches from which output signals are taken;
C. logic branch means connected to said signal generating means and said reference branch means for generating logic output signals the states of which are determined by a comparison between the voltage levels of said output signals from said signal generating means and the voltage levels of said reference signals;
and
D. output branch means connected to said logic branch means for receiving the logic output signals from said logic branch means for generating digital signals having predetermined voltage levels in response to the logic output signals from said logic branch means.

4 more elements

A source follower current steering logic circuit for performing a logic operation on a plurality of input signals comprising:

A. first and second input branches each including:
(i) input logic means each for receiving a plurality of input signals and for generating a signal in response to the received signals having selected conditions;
(ii) signal generating means connected to said input means and to a current source means for receiving the signal therefrom and for generating an output signal having a selected voltage level in response thereto, said signal generating means of both said first and second input branches having a corresponding predetermined number of level shifting diode means each having an output, connected serially between said current source means and said input means, the output signal from the signal generating means of one branch being taken from the output of a different level shifting means than the level shifting means from which the output signal is taken in the signal generating mean of the other branch have different voltage levels;
B. reference branch means having a plurality of serially-connected level shifting diode means, each having an output, connected to a current source means, said level shifting diode means of said reference branch means corresponding to the number of level shifting diodes means of said signal generating means of each of said input branches, the reference branch means generating reference voltage signals from the outputs of level shifting diode means corresponding to the level shifting diode means in each of said first and second input branches from which output signals are taken so that each reference voltage signals has a voltage level that is proportional to the voltage levels of an output signal of said signal generating means when said output signal is in a selected condition;
C. logic branch means connected to said signal generating means and said reference branch means for generating logic output signals in response to the voltage levels of said output signals from said signal generating means, the states of said logic output signals being determined by a comparison between the voltage levels of said output signals from said signal generating means and the voltage levels of said reference signals, said logic branch means including a plurality of transistor means each having a drain terminal, a source terminal and a gate terminal, each gate terminal being connected to receive one of said reference voltage signals or said output signals from said signal generating means, said source terminals of said transistor means which receive corresponding reference and output signals being connected together so that the transistor means which is controlled by an output signal is on only if the voltage level of the output signal is greater than the voltage level of the corresponding reference signal, the logic output signals being generated in response to the signals at the drain terminals of said transistor means;
and
D. Output branch means connected to said logic branch means for receiving the logic output signals from said logic branch means for generating digital signals having predetermined voltage levels in response to the logic output signals from said logic branch means, said output branch means including voltage reference input means for receiving an output voltage reference signal and anti-parallel diode means connected between the voltage reference input means and the drain terminals of said transistor means from which the logic output signals are received, the antiparallel diode means clamping the digital signals at voltage levels determined by the voltage level of said output voltage reference signal.

4 more elements

A source follower current steering logic circuit for performing a logic operation on a plurality of input signals comprising:

A. input branch means including first and second signal generating means each connected for receiving an input signal and for generating an output signal having a selected voltage level in response thereto, each said signal generating means having a corresponding predetermined number of voltage level shifting means connected serially, each having an output, with the output signal from one branch's signal generating means being taken from the output of a different level shifting means than the output signal of the signal generating means of the other input branch such that the output signals from the first and second signal generating means have different voltage levels.
B. reference branch means having a like number of serially-connected level shifting means, each having an output for generating reference voltage signals from the outputs of level shifting means, the reference voltage signals being taken from level shifting means which correspond to the level shifting means in each of said first and second signal generating means from which output signals are taken;
C. logic means including current mode logic switch means connected to said signal generating means and said reference branch means for performing a selected logic operation and, in response thereto, transmitting complementary logic output signals, said current mode logic switch means being connected to perform the selected logic operation in response to the output signals from said first and second signal generating means, the states of said logic output signals being determined by a comparison between the voltage levels of said output signals from said signal generating means and the voltage levels of said reference signals;
and
D. clamp means connected to said logic means for clamping said complementary logic output signals to predetermined voltage levels.

2 more elements

Dependencies are inferred from the claim text.