Hughes Aircraft Company

Phillip L Elliott

Lloyd Frederick Linder

Dwight D Birdsall

Kelvin T Tran

Donald G McMullin

A bias voltage source (20) produces a variable bias voltage (VBREF) which regulates the bias currents in an array (30) of transistor current switch cells (34,36) in an digital-to-analog converter (DAC). The bias voltage (VBREF) is applied to the bases of the regulating transistors (Q8') in the cells (34,36) to regulate the bias currents in their respective main transistors (Q6',Q7') to values proportional to the main bias current (IBIAS). Each main transistor (Q6,Q6',Q7,Q7') and regulating transistor (Q8,Q8') is provided with a compensating transistor (Q10,Q10')(Q11,-Q11') which sinks the emitter-base current thereof and cancels deviation of the actual current gain from the design current gain. Another compensating transistor (Q9,Q9') is connected to each regulating transistor (Q8,Q8') to cancel the effect of base-emitter voltage variation with temperature.

Transistor current switch array for digital-to-analog converter (DAC)

First and second current feedback transconductance amplifiers (102,104) each have a high impedance voltage input, a low impedance current input and a pair of push-pull current outputs. In a single-ended configuration, an input signal is applied to the voltage input of the first transconductance amplifier (102) and the push-pull outputs of the both transconductance amplifiers are connected through a current mirror (136,138) to a node (134) where the current outputs are summed. The node current is integrated by a capacitor (174) to produce a voltage which is amplified by a transimpedance amplifier (190) to produce an output voltage which is fed back to the voltage input of the second transconductance amplifier (104). The current inputs of the transconductance amplifiers (102,104) are interconnected by a resistor (132). The high impedance voltage inputs produce common-mode cancellation of distortion in the transconductance amplifiers (102,104) and low input shot noise. In a differential configuration, differential input signals are applied to the voltage inputs of transconductance amplifiers (260,262), and a separate transimpedance amplifier (292,316) and current mirror (278,280) (302,304) is provided for each transconductance amplifier (260,262). A common-mode feedback circuit (352) controls the common-mode output voltages of the transimpedance amplifiers (292,316) to ground. Switch means (402,404,406,408,410,412) may be added to selectively ground the voltage inputs of the transconductance amplifiers (260,262) and disable their input stages by disconnecting their power supplies (VCC,VEE).

Single-ended and differential amplifiers with high feedback input

A transconductance push-pull amplifier (20) generates primary push-pull currents (I1, I2) corresponding to a voltage input signal (VIN). Current mirrors (42,44) generate secondary push-pull currents (I3, I4) corresponding to the primary push-pull currents (I1, I2). For sampling, both the primary and secondary push-pull currents (I1, I2, I3, I4) are applied to charge a capacitor (C3) in a current feed-forward arrangement with high slew rate and fast signal acquisition to produce a voltage output signal (VOUT). The capacitor (C3) is disconnected from the amplifier (20) and current mirrors (42,44) to hold the output signal (VOUT). Switching transistors (Q13, Q15) which are connected between the capacitor (C3) and the current mirrors (42,44) have substantially the same non-linear modulation characteristics as corresponding output transistors (Q7, Q8) in the amplifier (20). The output and switching transistors (Q7, Q8, Q13, Q15) are connected to modulate out-of-phase such that non-linear modulation of the primary push-pull currents (I1, I2) by the output transistors (Q7, Q8) is canceled by non-linear modulation of the secondary push-pull currents (I3, I4) by the switching transistors (Q13, Q15), and the output signal (VOUT) is a highly linear replica of the input signal (VIN).

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Fort Collins, CO, United States of America

Phillip L Elliott