Wideband amplifier

An amplifier comprising a plurality of stacked current mirrors, each having an input and a common terminal, provides an output amplified current in response to receiving an input current at first and second inputs. A current source supplies a direct current to the input of the first one of the current mirrors while the input and the common terminal is also coupled to the first and second inputs of the amplifier. The common terminal of each preceding current mirror is coupled to the input of the next proceeding current mirror whereby the sum of the input and output currents of the preceding amplifier is sourced to the input of the proceeding current mirror. An output of the last one of the plurality of current mirrors is coupled to the output of the amplifier.

BACKGROUND OF THE INVENTION 
The present invention relates to amplifiers and, more particularly, to high 
frequency wideband amplifiers suited to be manufactured in monolithic 
integrated circuit form. 
The art is replete with high frequency amplifiers. Generally, most high 
frequency amplifiers have been fabricated using discrete components. Many 
of these prior art amplifiers require large component count, transformers 
and are expensive. In addition, such high frequency amplifiers require 
high power consumption and are not suited for use with battery operated 
power supplies. 
Presently, there is a need for an integrated linear wideband amplifier the 
gain and phase of which are consistent and predictable and which can be 
operated from a battery voltage while providing relatively high output 
power and low current drain. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide an 
improved amplifier. 
It is another object of the present invention to provide an improved high 
frequency wideband suited to be manufactured in integrated circuit form. 
Still another object of the present invention is to provide an integrated 
amplifier circuit which may be battery operated while having high output 
power and low current drain. 
In accordance with the above and other objects there is provided an 
amplifier comprising at least first and second current mirrors each having 
an input, an output and a common terminal and a current source for 
supplying a current to the input of the first current mirror; the input 
and the common terminal of the first current mirror being coupled to 
inputs of the amplifier for receiving a differential input signal while 
the output is coupled to power supply conductor; the input of the second 
current mirror being coupled to the common terminal of the first current 
mirror, the output of the second current mirror being coupled to an output 
of the amplifier and the common terminal being coupled to a second power 
supply conductor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Turning to FIG. 1 there is shown wideband amplifier 10 of the present 
invention which is suited to be manufactured in integrated circuit form. 
Amplifier 10 is illustrated as comprising a plurality of current mirrors 
18, 20 and 22 each having an input (shown by the semi-circle), an output 
and a common terminal. Although amplifier 10 is illustrated as having n 
current mirrors the novelty of the present invention is found in stacking 
first and second current mirrors in the manner to be described. 
First current mirror 18 is shown as having its input and common terminal 
coupled to inputs 12 and 14 respectively to which is received a 
differential input current I.sub.in. In addition, current source 24 
supplies a direct current I.sub.dc to the input of current mirror 18. The 
output of current mirrors 18 and 20 (via leads 30 and 32), as well as 
current source 24, are coupled to a first power supply conductor to which 
is supplied V.sub.cc. V.sub.cc may be a battery voltage. The common 
terminal of current mirror 18 is coupled to the input of current mirror 20 
while the common terminal of the latter is coupled to the input of current 
mirror 22. As illustrated, a plurality of current mirrors may be stacked 
between the common terminal of current mirror 20 and the input of n.sup.th 
current mirror 22 with each having their common terminals coupled to the 
input of the next proceeding current mirror as illustrated by current 
mirrors 20 and 22. Current mirror 22, being the last stage of the stacked 
current mirror stages, has its common terminal coupled to a second power 
supply conductor 28 to which is supplied a ground reference potential. The 
output of current mirror 22 is coupled to output 16 of amplifier 10 via 
lead 34. Each of the current mirrors will provide a current at its output 
which is a multiple of the supplied input current. For example, the output 
current at lead 30 from current mirror 18 is equal to: 
EQU (I.sub.dc +I.sub.in)(nl) (1) 
where n1 is the multiplication factor of current mirror 18, as is 
understood. 
Thus, the input current supplied to the input of current mirror 20 from the 
common terminal of current mirror 18 can be shown to be equal to: 
EQU I.sub.dc (n1+1)+I.sub.in (n1) (2) 
Similarly, the output of current mirror 20 provided at lead 32 is equal to: 
EQU [I.sub.dc (n1+1)+I.sub.in ](n2) (3) 
where n2 is the multiplication factor of current mirror 20. 
Thus, the output current, Io, provided at output 16 may be shown to be 
equal to: 
EQU [I.sub.dc (n1+1)+I.sub.in (n1)](n2+1) . . . (n.sub.n-1 +1)(n.sub.n) (4) 
Basically, then, the sum of the input and output currents of each preceding 
current mirror stage become the input current to the next following 
current mirror stage. Each preceding current mirror stage effectively 
presents a high output impedance current source to the following current 
mirror stage. Because the amplifier 10 is driven differentially, as is 
seen in FIG. 2, the input of current mirror 28 appears as a common emitter 
rather than as a common collector input to the driving source. This 
results in good matching between the input impedance of amplifier 10 and 
the driving source to the amplifier. As is evidence by the above 
equations, the stacked current mirrors 18 . . . 22 are utilized to build 
up the gain of amplifier 10. 
Referring now to FIG. 2, a complete schematic of amplifier 10 is 
illustrated wherein like components thereof are designated by the same 
reference numbers used in FIG. 1. It is apparent to those skilled in the 
art that amplifier 10 is suited to be manufactured in integrated circuit 
form using conventional low power bipolar integrated circuit processes. In 
the present case, amplifier 10 is comprised of three current mirror stages 
(n=3) that are stacked in the manner shown in FIG. 1. Relating back to the 
above, current mirror 18 is formed by diode connected transistor 40 and 
transistor 42 the connection therebetween being well known in the art. 
Transistor 40 functions as a semiconductor diode having its collector and 
base electrodes interconnected to the control or base electrode of 
transistor 42. The collector of transistor 40 acts as the input of the 
current mirror and is coupled both to input 12 and current source 24. The 
first or emitter electrodes of transistors 40 and 42 are interconnected at 
the common terminal of the current mirror while the collector or second 
electrode of transistor 42 (the output of the current mirror) is buffered 
via the collector-emitter conduction path of transistor 44 from power 
supply conductor 26, the base of the latter being coupled to a terminal at 
which a bias potential V.sub.B is provided. Transistors 46 and 48 function 
as the current mirror 20 with the collector of transistor 46 (the input of 
the current mirror) being coupled to the common terminal of the preceding 
current mirror). The bases of transistors 46 and 48 are interconnected 
with the emitter of transistor 50 and resistor 62. The collector of 
transistor 48 provides the output of the current mirror and is buffered 
from supply by cascoded transistors 44, 56 and 58. Similarly, transistor 
50 which has its collector coupled to the emitter of transistor 56 and its 
base coupled to input 14 buffers current mirror 20 from voltage swings to 
effectively increase the frequency response of transistor 48. The third 
current mirror is illustrated as comprising diode connected transistor 52 
and transistor 54 connected together in substantially the same manner as 
previously described in reference to first current mirror 18. Again, the 
output of the current mirror (the collector of transistor 54 is buffered 
from the output 16 of amplifier 10 by cascoded transistor 60 which can be 
switched on or off by an appropriate signal applied at terminal 62. 
Although amplifier 10 has been described above as having output 16 coupled 
to the collector of transistor 54 of current mirror 22, it is to be 
understood that an output of amplifier 10 can be taken from the common 
terminal of the aforementioned current mirror instead of the latter being 
coupled to conductor 28. 
Hence, what has been shown and described is a novel amplifier utilizing 
stacked current mirrors for amplifying a differentially applied input 
current. The sum of the input and output currents of each preceding 
stacked current mirrors provides the input current source to the input of 
the next proceeding stacked current mirror.