GB2057803A - Amplifiers - Google Patents

Abstract

A monolithic amplifier in which the bandwidth of the amplifier is considerably increased by using active components for matching purposes, consists of a common gate input stage coupled to a source follower output stage through an intermediate "transimpedance" stage. The transistors are preferably D-MESFET's fabricated in GaAs. <IMAGE>

Description

SPECIFICATION Improvements in or relating to electronic amplifiers The present invention relates to electronic amplifiers and more particularly to transimpedance monolithic GaAs amplifiers. Preferably the amplifiers are constructed as D-MESFET structures.

A problem with the present design of monolithic GaAs amplifiers is that the frequency of operation is a function of chip size when operating from 100 MHz to 4GHz due to the use of passive input and output matching networks. The present invention seeks to obviate this disadvantage by providing an actively matched amplifier.

The present invention will be described by way of example with reference to the accompanying drawings in which Figure 1 shows a first transimpedance actively matched monolithic D-MESFET GaAs amplifier according to the present invention, Figure 2 shows a second inventive transimpedance actively matched monolithic GaAs amplifier, Figure 3 shows a frequency response of the circuit of Fig. 1 Figure 4 shows a stability characteristic of the circuit of Fig. 1 and Figure 5 shows an input return loss characteristic for the circuit of Fig. 1.

Referring now to Figs. 1 and 2 of the drawings the transimpedance amplifiers shown comprise a common gate input section, a transimpedance amplifier section and a source follower output section.

The circuits shown achieve good input and output very broadband matching using D MESFETs configured to give matching without the need to use conventional passive matching networks and can give higher gain and wider bandwidth by using transimpedance stages with active or passive loads between the input and output stages. A higher circuit function density per unit area of GaAs can be achieved by using bias chain self biasing and on chip decoupiing techniques.

The circuits are improvements over the present techniques because no passive matching networks are used at the input and output so that the frequency of operation does not become a function of chip size when operating from, for example, 100 MHz to 4GHz or even wider bandwidth and higher gain per stage can be achieved than when using broadband single stages. A higher gain per arbitrary unit of phase shift is obtainable in comparison with a single stage stability is increased over single stages of comparable gain and is maintainable over a wider bandwidth.

If ion implantation techniques are used (giving closer IDSS/VP matching) the biasing component count may be reduced in such a manner to (1) use the same bias current for two stages and (2) remove bias components decreasing output capacitance and increasing bandwidth.

The applications for the invention are in the fields of multi octave amplifiers and very broadband limiters.

1. A transimpedance monolithic electronic amplifier including a common gate input stage and a source follower output stage and including a transimpedance amplifier stage connected between said gate input stage and said source follower stage to provide active matching for said amplifier.

2. An electronic amplifier as claimed in claim 1 in which the transimpedance amplifier includes an active load.

3. An electronic amplifier as claimed in claim 1 or claim 2 in which the construction is D-MESFET and the active semiconductor material is Ga As.

4. An electronic amplifier substantially as described with reference to figure 1 or figure 2 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements in or relating to electronic amplifiers The present invention relates to electronic amplifiers and more particularly to transimpedance monolithic GaAs amplifiers. Preferably the amplifiers are constructed as D-MESFET structures. A problem with the present design of monolithic GaAs amplifiers is that the frequency of operation is a function of chip size when operating from 100 MHz to 4GHz due to the use of passive input and output matching networks. The present invention seeks to obviate this disadvantage by providing an actively matched amplifier. The present invention will be described by way of example with reference to the accompanying drawings in which Figure 1 shows a first transimpedance actively matched monolithic D-MESFET GaAs amplifier according to the present invention, Figure 2 shows a second inventive transimpedance actively matched monolithic GaAs amplifier, Figure 3 shows a frequency response of the circuit of Fig. 1 Figure 4 shows a stability characteristic of the circuit of Fig. 1 and Figure 5 shows an input return loss characteristic for the circuit of Fig. 1. Referring now to Figs. 1 and 2 of the drawings the transimpedance amplifiers shown comprise a common gate input section, a transimpedance amplifier section and a source follower output section. The circuits shown achieve good input and output very broadband matching using D MESFETs configured to give matching without the need to use conventional passive matching networks and can give higher gain and wider bandwidth by using transimpedance stages with active or passive loads between the input and output stages. A higher circuit function density per unit area of GaAs can be achieved by using bias chain self biasing and on chip decoupiing techniques. The circuits are improvements over the present techniques because no passive matching networks are used at the input and output so that the frequency of operation does not become a function of chip size when operating from, for example, 100 MHz to 4GHz or even wider bandwidth and higher gain per stage can be achieved than when using broadband single stages. A higher gain per arbitrary unit of phase shift is obtainable in comparison with a single stage stability is increased over single stages of comparable gain and is maintainable over a wider bandwidth. If ion implantation techniques are used (giving closer IDSS/VP matching) the biasing component count may be reduced in such a manner to (1) use the same bias current for two stages and (2) remove bias components decreasing output capacitance and increasing bandwidth. The applications for the invention are in the fields of multi octave amplifiers and very broadband limiters. CLAIMS

1. A transimpedance monolithic electronic amplifier including a common gate input stage and a source follower output stage and including a transimpedance amplifier stage connected between said gate input stage and said source follower stage to provide active matching for said amplifier.

2. An electronic amplifier as claimed in claim 1 in which the transimpedance amplifier includes an active load.

3. An electronic amplifier as claimed in claim 1 or claim 2 in which the construction is D-MESFET and the active semiconductor material is Ga As.

4. An electronic amplifier substantially as described with reference to figure 1 or figure 2 of the accompanying drawings.