Amplifiers – With control of power supply or bias voltage – With control of input electrode or gain control electrode bias
Reexamination Certificate
2000-11-16
2001-12-04
Pascal, Robert (Department: 2817)
Amplifiers
With control of power supply or bias voltage
With control of input electrode or gain control electrode bias
C330S134000, C330S285000
Reexamination Certificate
active
06326842
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a variable gain amplifying apparatus which can set predetermined gain for amplifying.
2. Description of the Related Art
A variable gain amplifying apparatus has a plurality of digital control type amplifying circuits. A valid gain of the variable gain amplifying apparatus is equal to a total of specific gains of digital control type amplifying circuits to be made active. If the variable gain amplifying apparatus is provided with analog control type amplifying circuits, the valid gain of the variable gain amplifying apparatus is equal to a gain set for the analog control type amplifying circuit.
FIG. 1
shows a configuration of a conventional variable gain amplifying apparatus. A variable gain amplifying apparatus (VGA)
3
shown in
FIG. 1
has an input
301
, an output
302
, an n-bit controller
303
and first to n-th variable gain circuits
311
to
315
.
The input
301
is connected to an input of the first variable gain circuit
311
. An output of the first variable gain circuit
311
is connected to an input of the second variable gain circuit
312
. An output of the second variable gain circuit
312
is connected to an input of the third variable gain circuit
313
. Similarly, an output of the (n−1)-th variable gain circuit
314
is connected to an input of the n-th variable gain circuit
315
. An output of the n-th variable gain circuit
315
is connected to the output
302
. An output of the n-bit controller
303
is connected to control terminals of the first to n-th variable gain circuits
311
to
315
.
The input
301
is a terminal to which an input signal is inputted. The first variable gain circuit
311
is composed of variable amplifiers in which the gain (0 db, 32 dB) are set in accordance with a control signal outputted by the n-bit controller
303
. The second variable gain circuit
312
is composed of variable amplifiers in wihch the gain (0 dB, 16 dB) are set in accordance with the control signal outputted by the n-bit controller
303
. The third variable gain circuit
313
is composed of variable amplifiers in wihch the gain (0 dB, 8 dB) are set in accordance with the control signal outputted by the n-bit controller
303
. The (n−1)-th (fourth) variable gain circuit
314
is composed of variable amplifiers in wihch the gain (0 dB, 4 dB) are set in accordance with the control signal outputted by the n-bit controller
303
. The n-th (fifth) variable gain circuit
315
is composed of variable amplifiers in wihch the gain (0 dB, 2 dB) are set in accordance with the control signal outputted by the n-bit controller
303
. The output
302
is a terminal from which the amplification signal amplified by the first to n-th (fifth) amplifiers
311
to
315
is outputted. The n-bit controller
303
outputs an n-bit parallel signal to the first to n-th (fifth) variable amplifiers
311
to
315
. In this case, the n-bit implies a five-bit, corresponding to the first n-th (fifth) variable amplifiers
311
to
315
. The most significant bit of the n-bit is inputted to, for example, the first variable gain circuit
311
. In this case, the least significant bit of the n-bit is inputted to the n-th (fifth) variable gain circuit
315
. A variable gain circuit receiving a valid bit (a value of 1) is turned ON (the amplification of 32, 16, 8, 4 or 2 dB) . A variable gain circuit receiving an invalid bit (a value of 0) is turned OFF (the amplification of 0 dB). The gain of the variable gain amplifying apparatus
3
can be set to 0, 2, 4, . . . , or 32 db. By the way, the amplification degree of each variable gain circuit is not limited to the above-mentioned values. It may be set arbitrarily.
If the gain of the variable gain amplifying apparatus
3
is set to 2 dB, the n-bit controller
303
outputs a control signal (
00001
). In response to this control signal, the n-th (fifth) variable gain circuit
315
is turnedON (the gain of 2 dB), and the first to (n−1) (fourth) variable gain circuits
311
to
314
are turned OFF (the gain of 0 dB). If the gain of the variable gain amplifying apparatus
3
is set to 32 dB, the n-bit controller
303
outputs a control signal (
11111
). In response to this control signal, the first to n-th (fifth) variable amplifiers
311
to
315
are turned ON (the gain of 32+16+8+4+2 dB) . By the way, the control is not limited to the above-mentioned cases. It may be set arbitrarily.
If the amplifying circuits are connected in multiple stages, the total gain implies the total of the gains in the respective amplifying circuits. The values of the respective amplifying circuits are reflected in the total value of noise figures and distortion values.
FIGS. 2A
,
2
B show the characteristics of the variable gain amplifying apparatus.
FIG. 2A
shows the configuration to describe the performances of the variable gain amplifying apparatus
3
(FIG.
1
), and
FIG. 2B
shows the performance parameters of the variable gain amplifying apparatus.
A variable gain amplifying apparatus
3
shown in
FIG. 2A
is provided with an input
301
, an output
302
and first to n-th amplifying circuits
311
to
315
.
An input
301
is connected to an input of the first amplifying circuit
311
. An output of the first amplifying circuit
311
is connected to an input of the second amplifying circuit
312
. An output of the second amplifying circuit
312
is connected to an input of the third amplifying circuit
313
. Similarly, an output of the (n−1)-th amplifying circuit
314
is connected to an input of the n-th amplifying circuit
315
. An output of the n-th amplifying circuit
315
is connected to the output
302
.
The first amplifying circuit
311
has a gain G1. The second amplifying circuit
312
has a gain G2. The third amplifying circuit
313
has a gain G3. The (n−1) -th amplifying circuit
314
has a gain G(n−1). And, the n-th amplifying circuit
315
has a gain Gn. As for a noise figure NF, similarly, the first to n-th amplifying circuits have noise figures NF1 to NFn, respectively. As for a distortion IP3, similarly, the first to n-th amplifying circuits have distortions IP31 to IP32, respectively.
A total gain Gt (dB) of the variable gain circuit
3
(which is assumed to have three stages) is represented by the following equation 1:
Gt=G1+G2+G3+. . . +Gn
A total noise figure NFt (a true number) is represented by the following equation 2:
NFt=NF1+(NF2−1)/G1+(NF3−1)/(G1*G2)+. . . +(NFn−1)/(G1*G2*G3 . . . *G(n−1))
A total distortion IP
3
t (a true number) is represented by the following equation 3:
IP3t=1/(1/IP31+G1/IP32+G1*G2/IP33+G1*G2*G3* . . . *G(n−1)/IP3n)
As can be evident from the equation (2), if the noise figure NF1 of the first amplifying circuit is small and the gain G1 is large, the total noise figure NFt can be made smaller. On the other hand, the increase in the number of stages in the amplifying circuits causes the total noise figure NFt to be larger. In order to obtain a desirable total gain Gt, it is necessary that the amplifying circuit has a larger number of stages. In the conventional variable gain amplifying apparatus
3
, it is difficult to drop the total noise figure NFt.
The amplifying circuits are coupled in series. Thus, it is necessary that even the amplifying circuit whose gain is set to 0 dB is always made active. In the conventional variable gain amplifying apparatus
3
, it is difficult to drop a consumptive electric power.
The increase in the number of stages in the amplifying circuits constituting the variable gain amplifying apparatus causes the influence of the amplification characteristic of each amplifying circuit to be larger. The inaccurate setting of the gain of each amplifying circuit increases an error in the total gain Gp. The increase in the number of stages in the amplifying circuit constituting the variable gain amplifying apparatus and further the change in the total gain G
Choe Henry
Hayes Soloway Hennessey Grossman & Hage PC
NEC Corporation
Pascal Robert
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