A fully integrated 5.2‐GHz single‐ended‐in and single‐ended‐out 0.18‐μm CMOS Gilbert upconverter

Abstract

A novel compact microstrip bandpass filter with two or three transmission zeros has been developed by combining parallel coupling and end coupling. By giving two or three transmission paths to the signals, two or three transmission zeros have been realized. Experimental bandpass filters have been fabricated and measured, and the simulation and measurement results show the electrical performances to be almost in agreement. INTRODUCTIONA fully matched Gilbert upconversion micromixer output is demonstrated at 5.2 GHz using 0.18-m deep n-well CMOS technology. The circuit schematic is shown in Figure 1. A Gilbert micromixer [1] intrinsically has a single-ended input. The single-todifferential input stage of a Gilbert micromixer not only transforms an unbalanced signal into balanced signals, but also provides wideband impedance matching. A passive LC current combiner is applied at the upconversion-mixer output stage. An LC combiner has the ability to double the output current and converts the differential outputs into a single-ended output [2]. As illustrated in Figure 1, the upconversion micromixer consists of an LO Gilbert mixer core, a single-to-differential IF input, and an RF-output LC-current combiner with lowpass LC matching. The LO input signal is generated by a broadband 180°coupler in order to maintain balanced LO signals. Thus, the truly balanced operation of a CMOS Gilbert micromixer with a single-ended input and a single-ended output is achieved in this paper. A double-balanced Gilbert mixer has been widely used in RF IC design due to the excellent port-to-port isolation property. The separate feeding ports for IF (RF) and LO in a Gilbert upconverter (downconverter) provides good isolation between IF (RF) port and LO port. If the IF (RF) and LO signals that feed the Gilbert mixer are balanced, the IF-RF (RF-IF) and LO-RF (LO-IF) port-to-port isolation will be excellent in a Gilbert upconverter (downconverter). Of course, this fact will be observed when the output signals are taken differentially [3,4]. When the input signals are no longer balanced, good isolation properties can be accomplished if the Gilbert cell circuitry possesses good common-mode rejection. However, the common-mode rejection provided by the biased current source in a conventional Gilbert mixer deteriorates rapidly at high frequencies. CIRCUIT DESIGNA photograph of the fabricated circuit is shown in Figure 2. The die size is 0.93 ϫ 0.96 mm 2 . In order to implement the circuit, 0.18-m deep n-well CMOS technology is used. The commongate-biased transistor M 3 and common-source-biased transistor M 2 provide 180°out-of-phase transconductance gain when M 1 and M 2 are connected as a current mirror. All the NMOS transistors are in the deep n-wells to improve isolation; also, M 3 does not have the physical capability to cause an unbalance in the transconductance gain [5]. The common-gate-configured transistor M 3 possesses good frequency response, while the speed of commonsource-configured M 2 is improved drastically by adding a lowimpedance ...