Improved voltage regulators of a type wherein a feedback network is used for developing an error signal having a magnitude dependent upon the degree to which a portion of the voltage being regulated departs from a voltage proportional to the extrapolated bandgap potential of the material from which first and second semiconductor junctions in the network are formed. More particularly, this error signal is generated at the output of a differential-input amplifier which differentially compares (a) a relatively large reference potential (m+n) times the offset potential across the first semiconductor junction, and (b) a relatively small reference potential m times the offset potential across the second semiconductor junction, augmented by a portion of the voltage being regulated. The factor m is a positive number at least unity; and the factor n, a positive number less than unity. The first and second semiconductor junctions are operated with relatively high and relatively low respective densities of current flow through them. The error signal is applied as a control signal to apparatus for controlling the flow of current between the regulator output terminals, thereby regulating the voltage appearing between them.
There is provided a voltage regulator in which a ratio of a maximum current and a short circuit current is adjusted so that the maximum current is greatly increased and a short circuit current is made small. A first current limiting circuit for limiting a current value of an output voltage terminal is composed of P-channel MOS transistors (2, 4), an N-channel MOS transistor (3), and resistors (21 and 22). A second current limiting circuit for detecting a reduction in voltage of the output voltage terminal and limiting a current value of the output voltage terminal is composed of P-channel MOS transistors (2, 4), an N-channel MOS transistor (3), and resistors (20, 21, and 22). By using these circuits, the maximum current can be greatly increased and the short circuit current can be reduced.
A tail current source is provided. The tail current source may be used in amplifiers, in an error amplifier of an LDO, or the like, to achieve high PSRR. The tail current source includes a first current mirror, a capacitor, a resistive device, and a current mirror circuit. The current mirror circuit is operable to provide the tail current from an input current. The first current mirror is an n-type current mirror which diverts a small fraction of the DC current from the current mirror circuit. The capacitor and the resistive device are coupled in series with each other, and are coupled between VDD and the common gate node of the transistors in the n-type current mirror. Accordingly, the gates of the transistors in the first current mirror follow AC variations in VDD. This way, the effects of AC variations in VDD on the tail current are approximately cancelled.
7560993 - Amplifier - Owned by Frontend Analog and Digital Technology Corporation (Hsinchu,TW)
An amplifier has a self-bias circuit to generate the bias voltage for the input of the amplifying circuit in the amplifier, thereby simplifying the circuit complexity to reduce the size and cost of the amplifier.
An integrable shunt regulator includes two connection terminals to be connected between poles of a supply voltage source. A controllable semiconductor component has a control input and a load path connected to the two connection terminals. A differential amplifier has first and second inputs and an output connected to the control input of the controllable semiconductor component. First and second transistors have emitter terminals and interconnected base and collector terminals connected to one of the connection terminals. A first resistor is provided. The emitter terminal of the first transistor is connected to the first input of the differential amplifier and is connected through the first resistor to the other of the connection terminals. A series circuit of second and third resistors has a connection node connected to the second input of the differential amplifier. The emitter terminal of the second transistor is connected through the series circuit of the second and third resistors to the other of the connection terminals.
A multi-stage circuit has a first stage powered by the output voltage of a next stage. A current source within the first stage provides a tail current for a differential amplifier within the first stage. When the first stage has an operating voltage high enough for proper operation, this tail current is at a nominal level; if the voltage is too low for proper operation of the first stage, the tail current is below this nominal level. A comparator, which has one input coupled to a node within this current source, a second input coupled to a threshold voltage, and an output coupled to a control node within the next stage, provides an output indicative of whether or not the tail current is substantially at its nominal level. If tail current is too low, the comparator provides a forcing signal to the control node of the next stage which causes the output of the next stage to be at a substantially nominal level regardless of the voltage at its input, thus providing a suitably high voltage for the first stage to begin normal operation. When the tail current reaches its nominal level, the comparator output changes state to one which has little or no effect on the output voltage of the second stage, and normal operation of the overall circuit begins.
