| 摘要 |
A transconductor circuit has first and second half cascode mirror circuits. Each half cascode mirror circuit has a cascode transistor, an active transistor, a base current compensating transistor, and a current source connected at one side to a supply voltage and at another side to the cascode transistor. The cascode and active transistors are connected in series between the current source and a first reference potential node. The base current compensating transistor is connected between the supply voltage and the base of the active transistor, and has its base connected between the current source and the cascode transistor. The bases of the cascode transistors of the first and second half cascode mirror circuits are connected to a second reference potential. First and second output mirror circuits are connected to mirror a current in a respective active transistor of the first and second half cascode mirror circuits. When a balanced input voltage is applied to respective voltage input nodes between the cascode and active transistors, corresponding balanced output currents are produced by the first and second output mirror circuits. In floating implementation, a biasing current source is connected between the first reference potential node and ground, and a biasing circuit connected to reference the second reference potential to a potential on the first reference potential node. Since the circuit may be made entirely of NPN transistors, it can run much faster than if PNP transistors were employed. Since the circuit is operated as a "quasi open-loop" circuit, the speed of operation is also enhanced. The circuit can be operated in class AB operation, if desired, or, if desired, in a class B-like mode of operation. Additionally, the output current is independent of the beta of the transistors, and the circuit can sink current to the physical limits of the active transistor components, thus enabling a high dynamic range of operation.
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