| 摘要 |
Many signal processing applications of practical importance (for example, continuous-signal filtering) require high-precision temperature-insensitive transconductance elements. In accordance with one feature of this invention, a reference transconductance element is included in a control loop. The element consists of a MOSFET device or a MOSFET circuit in the loop. In the loop, the transconductance of the reference element is determined solely by the value and switching period of a switched-capacitor. The transconductance of the element is in effect thereby precisely matched against the conductance of the switched-capacitor. As the temperature of the chip varies, a control voltage is generated in the loop to maintain the transconductance of the reference element constant. This same control voltage is applied to other similar elements included in circuits (for example, filters) on the chip. In that way, the transconductances of these other elements are also matched to that of the switched-capacitor. Significantly, the time constants in the circuits are thus made substantially temperature-insensitive, being proportional only to the product of the switching period of the switched-capacitor and to the ratio of capacitances on the chip. In accordance with another feature of the invention, a switched-capacitor and a reference voltage source are utilized as a standard for establishing a prespecified current and maintaining it substantially independent of temperature variations. In one specific embodiment, this current is in turn utilized to bias an associated differential pair thereby to maintain its transconductance temperature-insensitive. |
