Overview

From APPLIED MICROWAVE & WIRELESS, VOL. 6, NO. 3, FALL 1994

Separate, three-section band-pass filters covering the 1.34 to 2.2 GHz and 1.84 to 2.7 GHz bands, with ?3 dB bandwidths of 86 6 MHz and 126 10 MHz, respectively, and matched closed-loop control circuits are described in this paper. The filters and control circuits are both fabricated using a standard 1-micron GaAs MESFET foundry process.

The control circuits generate filter tuning and Q-control bias voltages by tracking a sub-harmonic reference signal. The circuits automatically maintain the filter insertion loss to within 0.5 dB over a more than a 1.3:1 frequency-tuning range, and regulate the center-frequency and insertion loss to within better than 1.2 MHz and 0.3 dB over a temperature range of ?50 to +75 degrees Celsius.

Background

The integration of narrow-band filters in MMIC form offers the attractive advantages of small size and tenability. A further advantage is the integration of such filters with some other functions such as amplification and frequency conversion. This allows a complete module (for example, a microwave receiver) to be fabricated as a single chip resulting in a further size/cost reduction.

To compensate passive component losses that are relatively high in MMIC implementation, several Q-enhancement techniques have been used in filter design [1, 2, 3, 4, 5]. These techniques allow to achieve a 0 dB pass-band insertion loss by introducing negative resistance in filter resonators. Unfortunately, such a Q-enhancement makes MMIC filter performance very...