Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, consumer electronic equipment manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ” The terms “couple” and “couples” are intended to mean either an indirect or a direct electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections.
Please refer to
In order to further illustrate the operation of the embodiments in the present invention, please refer to
As shown in Formula 1, while
relates to a zero output; and while
relates to a pole output. If (gm*ro+1) is large enough, the pole in the Formula 1 will be far higher than the zero point so that the pole can be neglected. That is, by appropriately selecting the parameter of every transistors of the compensation circuit 350, it can offer the operational amplifier 301 an extra zero point for increasing more phase margin. In practice, the method of utilizing the compensation circuit 350 to compensate the operational amplifier 301 can improve at lease ten degree of phase margin of the entire system. On the other hand, in this preferred embodiment, by utilizing the current mirror mechanism, the compensation circuit 350 also can feedback the voltage control current Io through the transistors M17 through M20 to the high impedance output node A and B of the first stage amplifier circuit 110 of the operational amplifier 100. In this case, the phase delay of unity-gain frequency can be significantly reduced.
Please note that, in the above-mentioned embodiment, the controllable current source 311 is composed of the N-type Metal Oxide Semiconductor (NMOS) M21; the impedance unit 312 is composed of the N-type Metal Oxide Semiconductor (NMOS) M22 and M23; the capacitance unit 313 is composed of the N-type Metal Oxide Semiconductor (NMOS) M24; and the current mirror circuit 314 is composed of P-type Metal Oxide Semiconductor (PMOS) M17 through M20. However, the present invention does not limit to the components of the above-mentioned circuit units. That is, all electron elements, which are capable of providing the needed function of the circuit unit, also belong to the claimed invention. For example, in other embodiment, the controllable current source 311 also can be practiced by utilizing other electronic device (e.g., P-type Metal Oxide Semiconductor); the impedance unit 312 can be practiced by the single transistor or the single resistance; and the capacitance unit 313 also can be practiced by a capacitance. The present invention can change the internal structure and according to the design requirement, but the basic themes is constant. Additionally, the compensation circuit not only can co-operate with the operational amplifier with the above-mentioned conventional miller compensation mechanism or the pole-zero tracking mechanism (as shown in
In contrast to the related art amplifier circuit, the amplifier circuit of the present invention relates to a compensation circuit coupled to an output node of an operational amplifier. The compensation circuit generates a voltage-controlled current according to the input voltage of the operational amplifier and feedback the voltage-controlled current to the output node of the first stage amplifier circuit of the operational amplifier. Therefore, the amplifier circuits not only greatly reduces the phase delay of unity-gain frequency of the operational amplifier by the feedback of the voltage-controlled current, but also increases the phase margin of the operational amplifier and further widely improve the loop stability of the whole system by providing a zero point.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.