A Digitally Controllable Attenuator with an Accuracy of 0.2dB over 1-30GHz Based on a 16-bit Digital-to-Analog Converter

In order to meet the needs of fine resolution of attenuation in such applications as high accuracy multi-channel calibration and vector-modulators, a broadband attenuator with a digitally controllable step as fine as 0.2dB based on a 16-bit digital-to-analog converter (DAC) is proposed in this paper. The high-precision DAC generates an analog voltage with a resolution of up to 1mV, which is used to accurately control two cascaded voltage variable attenuator (VVA) chips. A prototype of the digitally controllable attenuator is designed and tested. Measurement results demonstrate that the proposed digitally controllable attenuator exhibit an attenuation range more than 34dB and attenuation accuracy of 0.2dB over 1-30GHz as bias voltage changed from -1V to 0V in steps of a couple of millivolts.

I. Introduction

Microwave attenuators are widely used in a variety of application systems such as RF communication systems, active phased array radar and test instruments. In the phased array system, the attenuators are applied to adjust the gain consistency between different channels and compensate the channel gain [1], [2], [3]. Attenuators are divided into digital step attenuator and voltage variable attenuator. The attenuation of the digital step attenuators are a series of discrete numerical values, while the voltage variable attenuator changes continuously with the bias voltage [4]. GaAs MMIC variable attenuators are widely used in many modern advanced electronic systems and equipment：1) broadband signal source; 2) acting as amplitude modulating or adjusting in a broadband vector modulator; 3) combining with a broadband amplifier to compose a broadband AGC (Auto-Gain Control) amplifier [5].