Solid-State Amplifiers/Oscillators Replaced BWOs And Klystrons

TRANSISTORS ARE A MAINSTAY OF THIS INDUSTRY- just as they have been for decades. In our August 1967 issue, for example, the Cover Feature spotlighted a family of 4-Gc (GHz) transistors that generated power to 75 mW. Hailing from Texas Instruments, the family comprised two transistors targeting practical oscillator applications above 4 Gc and a third device, which could be used in amplifiers to 4 Gc. This third device off ered guaranteed noise and gain performance at 2 Gc.

The L-187 and L-187A transistors were developed for use in fundamental-frequency oscillators. They provided typical output power of 40 and 75 mW, respectively, at 4 Gc (Fig. 1). Both devices could be tuned over octave ranges to an upper limit of roughly 6 Gc. The amplifier transistor, dubbed the L-186, offered a typical noise figure of 5 dB at 2 Gc. Under the same operating conditions, it offered common-emitter unneutralized gain of 8 dB.

The L-187 and L-187A oscillator transistors also were useful in amplifier circuits. They could deliver a somewhat higher saturated output than their sibling, the L-186. Although they offered similar gain to the L-186, they suffered a higher noise figure due to the higher operating current. These "silicon oscillators" promised to replace low-power backward-wave oscillators (BWOs) and reflex klystrons. In addition, the L-186 was used in single- and multi-stage amplifiers in place of tunnel diodes and low-power traveling-wave tubes (TWTs).

Looking back on these then cover-worthy products, one of their most standout features was their packaging. All three devices were NPN, double-diffused, epitaxial-planar siliconbipolar transistors. They were available in the firm's TI-LINE package for use in stripline circuitry (Fig. 2). The package had common-lead inductance of 0.16 nH with feedback capacitance of 0.02 pF. The L-187 and L-187A were designed for use in a common-base configuration while the L-186 was connected in common-emitter configuration.

Notably, the L-186 also came in TI's new microwave Pellet-Pak as well as an "experimental," miniature coaxial package. In the latter package, the transistor delivered a minimum common-emitter unneutralized gain of 5.5 dB at 4 Gc. The common-lead inductance of the coaxial package was 0.08 nH while feedback capacitance was 0.005 pF.