(A) study on the linearization methods for voltage-to-current converters and its application to phase difference network

Abstract

The continuous-time transconductance-C filter is the best way for high-frequency filtering. Because transconductances and capacitors are the only components required for realizing a filter, it can be readily be implemented in a fully integrated form. Transconductors in continuous-time filters should satisfy the following properties: wide input linear range, must be simple for a wide frequency response, and must be tunable dependent on some dc bias voltage or current. In this dissertation, three new transconductors and its application to 90-degree phase difference network (PDN) are described. All of the above cited circuits have been implemented in a double-poly double-metal CMOS 1.2㎛ process. The first transconductor consists of the basic source-coupled pair and cross-coupled bias circuits. The cross-coupled bias circuits are composed of a source follower and a transistor operating in the linear region. As the input voltage increases, the effective bias current increases. Due to the bias feedback technique, the THD less than 1% can be obtained for the differential input signal up to 60% of the supply voltages (±5V). The second transconductor is the same as the first one except additional current sources to increase the transconductance of the source follower transistors. Thereby the linearity characteristics are further improved, and the THD less than 1% can be obtained over the differential input signal up to 70% of the supply voltages. The second-order effects are considered in detail. The above transconductors are relatively simple suitable for high-frequency applications and tunable dependent on the dc bias current. The last proposed transconductor uses the triode biased transistors with current-shunt feedback which remains the drain-to-source voltage to a constant independent of the input voltage. The THD less than 1% can be obtained over the differential input signal up to the supply voltages. The triode transconductor is advantageous over previous circu...