Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – Unwanted signal suppression
Reexamination Certificate
2001-07-12
2002-05-14
Wells, Kenneth B. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
Unwanted signal suppression
C327S520000, C327S513000
Reexamination Certificate
active
06388510
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is related to a transconductance-capacitance filter system equipped with a transconductance-capacitance filter circuit and an adjusting circuit thereof.
For instance, transconductance-capacitance filter systems (will be referred to as a “gm-C filer system” hereinafter) are employed in portable electronic appliances such as portable telephone sets.
FIG. 7
schematically represents an example of conventional gm-C filter systems. This gm-C filter system is equipped with a transconductance-capacitance filter circuit (will be referred to as a “gm-C filter circuit hereinafter)
1
, and an adjusting circuit
16
for adjusting a cut-off frequency of this gm-C filter circuit
1
. The gm-C filter circuit
1
is arranged by employing a transconductance amplifier (will be referred to as a “gm amplifier” hereinafter)
1
a
and a capacitor
1
b,
and may constitute, for example, a low-pass filter. On the other hand, the adjusting circuit
1
b
is provided with an oscillator
3
having a gm amplifier
3
a
and a capacitor
3
b
, comparators
14
and
15
designed for waveform shaping operation, and a frequency comparator
13
. In this case, the gm amplifier
3
a
of the oscillator
3
owns the same structure as that of the gm amplifier
1
a
of the gm-C filter circuit
1
.
In the gm-C filter system arranged in the above-explained manner, an oscillation signal OSC is supplied from the oscillator
3
via the comparator
14
to the frequency comparator
13
, and also a reference clock signal CK is supplied from an externally provided crystal oscillator (not shown) via the comparator
15
to this frequency comparator
13
, so that the frequency of the oscillation signal OSC is compared with the frequency of the reference clock signal CK. In other words, in the frequency comparator
13
, a bias current “i
BIAS
” is produced based upon a frequency error of the oscillation signal OSC with respect to the reference clock signal CK. This bias current “i
BIAS
” is supplied to the gm amplifier
3
a
employed in the oscillator
3
so as to adjust a value of a transconductance (will be referred to as a “gm value” hereinafter) of the gm amplifier
3
a
. For example, in such a case that the oscillation frequency of the oscillator
3
is higher than the frequency of the reference clock signal CK corresponding to the set value, such a bias current “i
BIAS
” capable of reducing the gm value of the gm amplifier
3
a
employed in the oscillator
3
is outputted from the frequency comparator
13
, so that the oscillation frequency of the oscillator
3
is reduced. Conversely, in such a case that the oscillation frequency of the oscillator
3
is lower than the frequency of the reference clock signal CK corresponding to the set value, such a bias current “i
BIAS
” capable of increasing the gm value of the gm amplifier
3
a
employed in the oscillator
3
is outputted from the frequency comparator
13
, so that the oscillation frequency of the oscillator
3
is increased. In other words, the bias current “i
BIAS
” is varied in such a manner that the oscillation frequency of the oscillator
3
is made coincident with the frequency of the reference clock signal CK, so that the gm value of the gm amplifier
3
a
employed in the oscillator
3
is adjusted.
On the other hand, the bias current “i
BIAS
” supplied from the frequency comparator
13
is also supplied to the gm amplifier
1
a
provided in the gm-C filter circuit
1
so as to adjust the gm value of this gm amplifier. As a result, the cut-off frequency is adjusted. In this case, since the gm amplifier
3
a
of the oscillator
3
owns the same structure as that of the gm-C filter circuit
1
, the oscillation frequency of the oscillator
3
may correspond to the cut-off frequency of the gm-C filter circuit
1
in an one-to-one correspondence relationship. As a consequence, in order to set the cut-off frequency of the gm-C filter circuit
1
to a desirable frequency value, the oscillation frequency of the oscillator
3
may be adjusted based upon such a frequency clock signal CK having a frequency corresponding to this desirable frequency value.
However, in the above-explained conventional gm-C filter system, there is such a serious problem. That is, the adjusting circuit
16
arranged by the oscillator
3
, the comparators
14
/
15
, and the frequency comparator
13
is continuously operated so as to adjust the cut-off frequency of the gm-C filter circuit
1
. Since this adjusting circuit
16
is continuously operated, the power consumption of the entire gm-C filter system would be increased.
SUMMARY OF THE INVENTION
The present invention has been made to solve such a conventional problem, and therefore, has an object to provide a gm-C filter system having low power consumption.
To achieve the above-described object, according to a first aspect of the present invention, a transconductance-capacitance filter system comprises: a transconductance-capacitance filter circuit including a transconductance amplifier and a capacitor; an adjusting circuit including an oscillator containing a transconductance amplifier having the same structure as that of the transconductance amplifier of the transconductance-capacitance filter circuit, the adjusting circuit producing a digital adjusting value used to adjust the transconductance of the transconductance amplifier of the oscillator based upon an oscillation signal outputted from the oscillator; a register for holding the digital adjusting value supplied from the adjusting circuit; and a D/A converter for converting the digital adjusting value held in the register into an analog adjusting value which is used to adjust the transconductance of the transconductance amplifier of the transconductance capacitance filter circuit; wherein the adjusting circuit is operated in an intermittent manner.
A transconductance-capacitance filter system, according to a second aspect of the present invention, transconductance further comprises a temperature sensing circuit for sensing an ambient temperature of the transconductance-capacitance filter system, and wherein the adjusting circuit is operated in the intermittent manner based upon a change contained in the ambient temperatures.
A transconductance-capacitance filter system, according to a third aspect of the present invention, transconductance further comprises a power supply voltage sensing circuit for sensing a power supply voltage of the transconductance-capacitance filter system, and wherein the adjusting circuit is operated in the intermittent manner based upon a change contained in the power supply voltages.
A transconductance-capacitance filter system, according to a fourth aspect of the present invention, transconductance further comprises a temperature sensing circuit for sensing an ambient temperature of the transconductance capacitance filter system, and a power supply voltage sensing circuit for sensing a power supply voltage of the transconductance-capacitance filter system, and wherein the adjusting circuit is operated in the intermittent manner based upon either a change contained in the ambient temperatures or a variation of the power supply voltages.
Also, according to a fifth aspect of the present invention, a transconductance-capacitance filter system comprises: a transconductance-capacitance filter circuit including a transconductance amplifier and a capacitor; an adjusting circuit including an oscillator containing a transconductance amplifier having the same structure as that of the transconductance amplifier of the transconductance-capacitance filter circuit, the adjusting circuit producing a digital adjusting the transconductance of the transconductance amplifier of the oscillator based upon an oscillation signal outputted from the oscillator; a register for holding the digital adjusting value supplied from the adjusting circuit; a D/A converter for converting the digital adjusting value held in the register into an analog adjusting value which is used to adjust the transconductance of the transconductance amplifi
Doushoh Shiro
Fujiyama Kunihiro
Hayashi Hiroki
Katada Tomoyuki
Morie Takashi
Matsushita Electric - Industrial Co., Ltd.
Nguyen Hai L.
Pearne & Gordon LLP
Wells Kenneth B.
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