Abstract: A phase locked loop system has a voltage-controlled variable-load ring oscillator (VLCO) that operates in a frequency band determined by a selected load on each stage of the ring oscillator. Each stage of the VLCO has multiple load selection transistors, each coupled to a load capacitor. Apparatus is provided for driving the load selection transistors according to a load configuration; and apparatus is provided for determining an operating load configuration such that a period of a divided reference signal approximately matches a period of a divided VLCO signal with the VLCO control voltage input clamped to a reference voltage. Once the load configuration is set, the loop is allowed to lock. In a particular embodiment, devices are provided for slowly tweaking the VLCO load to help keep the VLCO operating near an optimum control voltage despite drift of circuit parameters with temperature or time.

Abstract: A digital level shifter adapted to shift an input signal from switching in a low voltage range, to an output switching in a high voltage range has a glitch generator configured to generate pulses at rising and falling transitions of the input signal. Glitch generator output triggers a multiple-level current source to a high current mode, operating in a low current mode at other times. The current source feeds a differential pair of high voltage transistors with a first transistor of the pair having a gate coupled to the input signal and a second transistor of the pair having a gate coupled to a complement of the input signal. An active load and buffer circuit receives current from the differential pair and drives the output accordingly.

Abstract: A digital level shifter adapted to shift an input signal from switching in a low voltage range, to an output switching in a high voltage range has a glitch generator configured to generate pulses at rising and falling transitions of the input signal. Glitch generator output triggers a a multiple-level current source to a high current mode, operating in a low current mode at other times. The current source feeds a differential pair of high voltage transistors with a first transistor of the pair having a gate coupled to the input signal and a second transistor of the pair having a gate coupled to a complement of the input signal. An active load and buffer circuit receives current from the differential pair and drives the output accordingly.

Abstract: A phase locked loop system has a voltage-controlled variable-load ring oscillator (VLCO) that operates in a frequency band determined by a selected load on each stage of the ring oscillator. Each stage of the VLCO has multiple load selection transistors, each coupled to a load capacitor. Apparatus is provided for driving the load selection transistors according to a load configuration; and apparatus is provided for determining an operating load configuration such that a period of a divided reference signal approximately matches a period of a divided VLCO signal with the VLCO control voltage input clamped to a reference voltage. Once the load configuration is set, the loop is allowed to lock. In a particular embodiment, devices are provided for slowly tweaking the VLCO load to help keep the VLCO operating near an optimum control voltage despite drift of circuit parameters with temperature or time.

Abstract: A GaAs logic circuit including a current control FET that provides high current for switching an output FET, but limits the forward biasing of the output FET at the end of a transition to input logic 1 by controlling the steady state value of current to a gate of the output FET, which limits the voltage applied to the gate of the output FET to a given value. A bias circuit referenced to the voltage applied to the source of the output FET applies a nominal gate voltage to the current control FET. The value of the nominal gate voltage is such as is required to limit the value of the steady state current to the gate of the output FET to that which limits the voltage applied to such gate to the desired given value. Such nominal gate voltage is obtained by shifting the source voltage by the amount of the nominal threshold voltage V.sub.Te of an enhancement-mode FET of the bias circuit. If the nominal threshold voltage V.sub.

Abstract: A GaAs logic circuit uses a first FET to control the application of a logic signal from an input to an output. The first FET inherently has parasitic gate-to-source and gate-to-drain diodes. A control signal applied to the gate of the first FET controls the application of the logic signal to the output through the first FET. For a first FET that is an enhancement mode GaAs device, the gate current tends to forward bias such diodes under all operating conditions and tends to significantly increase the gate current. For a first FET that is a depletion-mode device, adverse operating temperatures can cause such tendency to forward bias these diodes and other circuit diodes. A limiter FET connected to the gate to limit the gate current and thus limits the forward biasing of the parasitic and circuit diodes. This reduces the effect on the gate current of variations in the power supplies to the FET, process variations and operating temperature variations.

Abstract: A circuit uses a pair of transistors in series to provide an output pulse which indicates an address transition has occurred. A duration of joint conductivity of the pair of transistors determines the duration of the output pulse. For an address transition, one of the transistors is rapidly turned on while the other is slowly turned off with a slow fall time. The fall time is adjustable to achieve an adjustable duration of joint conductivity, and thereby an adjustable output pulse width.

Abstract: A four-state ROM cell is improved by providing a tapered potential gate area which allows for the effective gate width to be increased and the gate length to be decreased for each succeedingly higher gain state with a single program mask at the polysilicon gate deposition stage.

Abstract: A TTL to CMOS input buffer accomplishes buffering a TTL signal to a CMOS signal without static current flow when the TTL is a logic "1" by isolating the input from an input P channel transistor and using feedback from an input N channel transistor to turn off the P channel transistor. A second P channel transistor is used to couple a positive power supply voltage to the input P channel transistor in response to an output from the N channel transistor.

Abstract: A CMOS level shifter with a reference voltage generator provides a TTL to CMOS input buffer. The reference voltage generator provides a reference voltage which is responsive to the voltage level of the TTL input signal. The reference voltage is kept sufficiently low to prevent an input P channel transistor from turning on when the TTL input signal is at a logic high even when the voltage level is at a minimum for a logic high.

Abstract: A TTL to CMOS input buffer accomplishes buffering a TTL signal to a CMOS signal without requiring current flow through a CMOS input inverter in a static condition by introducing a reference voltage to match the lowest level of a logic "1" of the TTL signal. The input inverter has a P channel transistor which, by having a source at the reference voltage, does not turn on when the TTL signal is at the lowest level of a logic "1". The reference voltage is selected to be less than the lowest level of a logic "1" minus the threshold voltage of the P channel transistor.

Abstract: A reference voltage generator uses a resistor divider technique to develop a reference voltage, but a resistor is replaced by a transistor to provide improved compensation for changes in a power supply voltage. The transistor is coupled to provide resistance which varies inversely to variations in power supply voltage.