Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – Unwanted signal suppression
Reexamination Certificate
2002-07-24
2004-10-19
Le, Dinh T (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
Unwanted signal suppression
C327S552000
Reexamination Certificate
active
06806765
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transconductance-capacitance filter, and a method of verifying transfer characteristics in a transconductance-capacitance filter. More particularly, the present invention relates to a transconductance-capacitance filter, and a method of verifying the transfer characteristic of a high-frequency integrated continuous-time filter of a transconductance-capacitance (gm-C) type.
2. Description of the Background Art
The four basic linear operations (integration, scaling, summation, inversion) used to synthesize a large class of transfer functions can be easily implemented using only transconductors and capacitors. For example, a transconductor loaded with a capacitor acts as a voltage input—voltage output integrator. Scaling is done by changing the transconductance of the transconductor and/or the capacitance of the load capacitor. The output currents of a plurality of transconductors can be summed by tying the outputs to a same node. Also, inversion can be done for instance by crossing inputs of a transconductor.
The basic building block of a transconductance-capacitance filter is a multiple input transconductance-capacitance integrator. This block can perform all of the above noted basic operations. The filter appears as a collection of interconnected multiple input transconductance-capacitance integrators. In an integrated circuit, both the transconductance of the transconductor and the capacitance of the capacitor are subject to influences such as fabrication processes, power supply and temperature variations. Thus, it is required to check the conformity of the implemented transfer function and to tune the filter so as to fulfill the designed function. Most of the tuning effort is directed toward adjusting the transconductance of the transconductors.
One of the conventional direct methods of checking the transfer function of a continuous-time filter consists of applying a constant amplitude, variable (sweeping) frequency sinusoidal signal at the input of the filter and measuring the amplitude and the phase of the resulting waveform at the output of the filter. Indirect methods, in contrast, analyze the step response of the filter. These known methods require the generation of a test signal (either on-chip or off-chip), applying the test signal at the input of the circuit under test (CUT), and reading and processing the response of the circuit. This can be done either on-chip or off-chip. For tuning purposes, the response of the filter is used in a feedback configuration to adjust its parameters.
FIGS. 1-5
are block diagrams showing circuit configurations of conventional checking methods.
FIG. 1
is a block diagram showing a testing circuit
100
for an integrated filter with an external test signal source
105
and an external generic analyzer
145
. As shown in
FIG. 1
, the testing circuit
100
includes an input buffer
110
coupled to the output of external test signal source
105
, a circuit under test (CUT)
115
, an output buffer
140
that provides an output to external analyzer
145
, first switch
130
connected between input buffer
110
and CUT
115
, second switch
135
connected between CUT
115
and output buffer
140
, and an internal circuit
120
connected to receive a signal from second switch
135
and to provide a signal to first switch
130
. In this circuit, input buffer
110
, CUT
115
, internal circuit
120
, first and second switches
130
and
135
, and output buffer
140
are all formed on a semiconductor chip
150
, while the external test signal source
105
and the external analyzer
145
are formed off the chip
150
.
The CUT
115
can be connected through the first and second switches
130
and
135
either to the internal circuit
120
, or to the input and output buffers
110
and
140
. When connected to input and output buffers
110
and
140
by first and second switches
130
and
135
, CUT
115
is connected to the external test signal source
105
and the external analyzer
145
. The first and second switches are controlled by switching signals SW. The switching signals SW indicate either a normal operation state (connecting the switches
130
and
135
to normal nodes N), or a test operation state (connecting the switches
130
and
135
to test nodes T).
FIG. 2
is a block diagram showing a testing circuit
200
for an integrated filter that is similar to the circuit shown in FIG.
1
. However, an external analog-to-digital converter (ADC)
255
and digital signal processor (DSP)
260
are included in place of external analyzer
145
of FIG.
1
. The testing circuit
200
of
FIG. 2
is thus similar to the testing circuit
100
of
FIG. 1
, but the analyzer device is DSP-based. In this circuit shown in
FIG. 2
, input buffer
110
, CUT
115
, internal circuit
120
, first and second switches
130
and
135
, and output buffer
140
are all formed on a semiconductor chip
250
, while the external test signal source
105
, the external ADC
255
, and the external DSP
260
are formed off chip
250
. The external ADC
255
of the testing circuit
200
acts as the interface between the CUT
115
and the DSP
260
. Since the ADC
255
is external, it can also be used for other functions external to the chip
250
.
FIG. 3
is a block diagram showing a testing circuit
300
for an integrated filter that is similar to the circuit shown in FIG.
2
. However, an internal ADC
355
is provided on the semiconductor chip
350
, in place of output buffer
140
of FIG.
2
. Also, external ADC
255
of
FIG. 2
is not included in the circuit as shown in FIG.
3
. The internal ADC
355
is coupled to receive an output from second switch
135
and provides an output directly to external DSP
260
. Internal ADC
355
is dedicated to test/tuning purposes. In this circuit as shown in
FIG. 3
, input buffer
110
, CUT
115
, internal circuit
120
, first and second switches
130
and
135
, and internal ADC
355
are all formed on semiconductor chip
350
, while the external test signal source
105
and the external DSP
260
are formed off chip
350
. Since the internal ADC
355
is disposed on semiconductor chip
350
, there is no need for an analog output buffer on chip
350
for testing the CUT
115
. In operation, the chip
350
receives an analog test signal, and outputs a digital test signal.
FIG. 4
is a block diagram showing a testing circuit
400
for an integrated filter that is similar to the circuit shown in FIG.
3
. However, internal test signal source
405
is provided on semiconductor chip
450
, in place of external test signal source
105
of FIG.
3
. Internal test signal source
405
provides a test signal directly to first switch
130
. Input buffer
110
of
FIG. 3
is not included in the circuit as shown in FIG.
4
. Also, an internal DSP
460
is provided on chip
450
, in place of external DSP
260
of FIG.
3
. Internal DSP
460
directly receives an output of internal ADC
355
. Internal DSP
460
is dedicated to test/tuning purposes. In this circuit as shown in
FIG. 4
, internal test signal source
405
, CUT
115
, internal circuit
120
, first and second switches
130
and
135
, internal ADC
355
, and internal DSP
460
are all formed on semiconductor chip
450
. Since the signal source
405
and the ADC
355
are both internal, there is no need for input and output buffers on chip
450
for testing the CUT
115
. In operation, chip
450
generates input signals internally, and outputs a digital signal.
FIG. 5
is a block diagram showing a testing circuit
500
for an integrated filter that is similar to the circuit shown in FIG.
4
. However, CUT
115
and internal ADC
555
are formed on main circuit
570
. In other words, the internal ADC
355
of
FIG. 4
is moved to be part of main circuit
570
as shown in FIG.
5
. Internal ADC
555
receives an output directly from CUT
115
, and provides an output to second switch
135
. As previously, CUT
115
receives an input from first switch
130
. In the circuit of
FIG. 5
, the internal
Le Dinh T
Oki America Inc.
Volentine & Francos, PLLC
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