Amplifiers – With semiconductor amplifying device – Including gain control means
Reexamination Certificate
2000-01-19
2001-12-18
Pascal, Robert (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including gain control means
C330S051000, C330S12400D
Reexamination Certificate
active
06331804
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an amplifier used at a receiving front end of a digital radio communication apparatus.
It also relates to a single side phase converter circuit for amplifying by single side phase conversion.
2. Description of the Related Art
In mobile communication, since the receiving electric field varies significantly depending on the distance between the base station and a mobile communication terminal, a wide dynamic range is required in the receiving system, and a gain control function is demanded in the low noise amplifier at the receiving front end. Besides, in the large-scale integration trend of the circuit, signal branching is indispensable in an integrated circuit.
Also in mobile communication, double side phase signals, it is advantageous to use double side phase signals because the incoming noise applied simultaneously in signal lines is eliminated. Thus, in the integrated circuit, this constitution is widely employed not only in the amplifier but also in the multiplier, oscillator and others. However, when a filter corresponding to double side phase signals is formed in the integrated circuit, the required area for inductor and capacitor is twice as wide as in the single side phase composition. Accordingly a circuit for converting a double side phase signal into a single side phase output is also needed. As the single side phase converter, it is general to connect the buffer of emitter follower type to the single side phase output of the differential amplifier.
A conventional variable gain amplifier is described below.
In a circuit diagram of a conventional variable gain amplifier in FIG.
13
, a cascade amplifier is composed of transistors
1301
,
1302
, resistors
1303
,
1304
, inductor
1305
, grounding capacitor
1306
, input matching circuit
1307
, output matching circuit
1308
, gain control terminal
1309
, power source terminals
1310
,
1311
, radio frequency input terminal
1312
, and radio frequency output terminal
1313
.
In this amplifier, in the case of weak input electric field, voltage Vagc
1
for obtaining a high gain is applied to the gain control terminal
1309
. At this time, the circuit composition of input matching circuit
1307
and output matching circuit
1308
and the inductance of inductor
1305
is set so that the input and output impedance of the amplifier coincide with the characteristic impedance of the transmission line. On the other hand, in the case of strong input electric field, voltage Vagc
2
for low fain (Vagc
2
<Vagc
1
) is set in the gain control terminal
1309
so that the gain of the amplifier is decreased.
In the conventional constitution of the variable gain amplifier, however, when changing over the gain, the input impedance of the amplifier varies. Then the input impedance mismatches with the characteristic impedance of the transmission line. Moreover since the gain is decreased by lowering the current of transistor, higher order distortion due to nonlinear effect increases.
In a conventional signal branching method, two stages of amplifiers are prepared, and the signal is branched off by the output of the first stage amplifier, and the signal is amplified again by the second stage amplifier, thereby compensating for the loss due to branching.
Besides, in the conventional signal branching constitution, to branch the signal into a plural lines, a large current must be passed in the first stage amplifier.
A conventional single side phase converter is described.
FIG. 14
is a circuit diagram showing a conventional constitution of single side phase converter. In
FIG. 14
, a differential amplifier
700
is composed of a direct-current voltage source
704
, transistors
707
and
708
sharing a common emitter terminal, a load resistor
706
connected to the collector side of the transistor
708
, and a current source
709
connected to the common emitter terminal of the transistors
707
,
708
. An emitter follower
1100
is composed of a transistor
1101
and a direct-current current source
1102
connected to the emitter of the transistor
1101
. In addition,
FIG. 14
further shows a common mode signal input terminal
702
, an inverting phase signal input terminal
703
for receiving a signal differing in phase by 180 degrees from that of the common mode signal input terminal
702
, and an output terminal
712
.
In thus constituted single side phase converter, the operation is described below.
First, double side phase signals input from the common mode signal input terminal
702
and inverting phase signal input terminal
703
are amplified by the differential amplifier
700
. At this time, a negative phase output signal appears at the collector terminal of the transistor
707
, and a positive phase output signal appears at the collector terminal of the transistor
708
. By picking up this positive phase output signal through the load resistor
706
, the double side phase signal can be converted into a single side phase signal. It is a common practice to omit the load resistor of the transistor
707
which does not pick up signal. Consequently, this positive phase output signal is taken out after converting the impedance in the emitter follower
1100
which is a non-inverting amplifier.
In this constitutions of the single side phase converter, since only the positive phase output of the double side phase output is taken out, half of the consumption current is not used. Another problem is that it is not possible to eliminate the in-phase noise which is an advantage of double side phase driving.
SUMMARY OF THE INVENTION
It is hence an object of the invention to present an amplifier keeping input matching and having an excellent higher order distortion characteristic even when changing over the gain by changeover of circuit by making use of cut-off voltage of transistor, and an amplifier realizing signal branching without requiring large current.
The variable gain amplifier of the invention is capable of obtaining a variable gain by changing over lines differing in the gain. It comprises at least a line having a cascade amplifier and a line having a base-ground-type-amplifier. Control terminals are provided independently in the cascade amplifier and base-ground amplifier, and the amplification factor is varied by changing over the control terminals.
Thus, a variable gain amplifier keeping input matching and having an excellent higher order distortion characteristic even when changing over the gain is obtained.
Moreover, an amplifier realizing signal branching without requiring large current is obtained.
The invention also presents an amplifier for amplifying a positive phase input signal by a non-inverting amplifier, amplifying a negative phase input signal by an inverting amplifier and connecting the both outputs through a coupling capacitor. Thereby the amplifier retains the feature as eliminating in-phase noise and converts the double side phase output into single side phase output efficiently.
The amplifier of the invention capable of converting an input signal into single side phase output signal is composed of a non-inverting amplifier for amplifying an input signal in positive phase and an inverting amplifier for amplifying the signal by inverting the phase, in a single side phase converter for converting double side phase input signal into single side phase signal and issuing. In the amplifier, signals of opposite phases are applied into the non-inverting amplifier and inverting amplifier respectively, and their outputs are connected through first and second coupling capacitors.
REFERENCES:
patent: 4348645 (1982-09-01), Ushida et al.
patent: 5327097 (1994-07-01), Igarashi et al.
patent: 5880639 (1999-03-01), Sakuragi
patent: 5903854 (1999-05-01), Abe et al.
patent: 6011431 (2000-01-01), Gilbert
patent: 6118989 (2000-09-01), Abe et al.
patent: 1-30312 (1989-02-01), None
Saito Noriaki
Shimizu Yoshito
Yabuki Hiroyuki
Matsushita Electric Industria, Co., Ltd.
Nguyen Khanh Van
Pascal Robert
Ratner & Prestia P.C.
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