Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – Nonlinear amplifying circuit
Reexamination Certificate
2002-12-12
2004-02-24
Zweizig, Jeffrey (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
Nonlinear amplifying circuit
Reexamination Certificate
active
06696888
ABSTRACT:
BACKGROUND OF THE INVENTION
FIG. 1
is a schematic diagram of a prior art RMS-DC converter system. The system of
FIG. 1
includes an RMS-DC converter subsystem
10
, a variable gain amplifier (VGA)
12
, and an operational amplifier (op amp)
14
.
The subsystem
10
performs an implicit RMS computation and includes an absolute value/voltage-current converter
16
, a one-quadrant squarer/divider
18
, and a current mirror
20
. The input voltage V
1
, which can be either AC or DC, is converted to a unipolar current I
1
by an active rectifier formed by op amps A
1
and A
2
. The current I
1
drives the input of the squarer/divider. The output current I
4
of the squarer/divider drives the current mirror through a low-pass filter formed by resistor R
1
and capacitor C
AV
. If the R
1
,C
AV
time constant is much greater than the longest period of the input signal, then I
4
is effectively averaged.
The current mirror returns a current I
3
, which equals the average of I
4
, back to the squarer/divider to complete the implicit RMS computation. The current mirror also produces the output current I
OUT
, which can be used directly or converted to a voltage with R
L
. An optional dB output can be derived from the emitter of Q
3
since the voltage at this point is proportional to −log V
1
. Emitter follower transistor Q
5
buffers and level shifts this voltage so that the dB output voltage is zero when the externally supplied emitter current I
REF
to Q
5
approximates I
3
.
The RMS subsystem
10
of
FIG. 1
can operate independently as a complete RMS-DC converter. However, it suffers from numerous problems such as limited dynamic range, and bandwidth that depends on the signal level. To overcome these problems, the system of
FIG. 1
utilizes the RMS subsystem as merely the detector element in an automatic gain control (AGC) loop in which the difference between the RMS output of the subsystem
10
and a fixed DC reference are nulled in a loop integrator. The loop integrator includes an op amp
16
and a variable gain amplifier (VGA)
12
. The op amp generates the output voltage V
OUT
in response to the output voltage V
RMS
from the RMS subsystem and the reference voltage V
REF
. Resistors R
6
and R
7
divide V
OUT
to generate the gain control signal V
G
, which controls the gain of the VGA. The dynamic range and accuracy with which the signal can be determined are now entirely dependent on the VGA. Since the input to the RMS subsystem is forced to a constant amplitude, close to its maximum input capability, the bandwidth is no longer signal dependent.
Although the system of
FIG. 1
can perform wide dynamic range RMS-DC measurements, it suffers from other limitations. For example, the circuitry in the RMS subsystem limits the maximum frequency at which the system can operate. There is also some redundancy, inasmuch as there is no need to compute the full root mean-square value.
SUMMARY
In one aspect of the present invention, an RMS-DC converter utilizes a variable gain amplifier to drive a squaring cell. In another aspect of the present invention, an RMS-DC converter drives a first squaring cell with a variable gain amplifier and drives a second squaring cell with a reference signal. In a further aspect of the present invention, an RMS-DC converter drives a first detector with a signal to be measured, and a second detector with a replica signal. In another aspect of the present invention, a variable gain amplifier is utilized to amplify either the signal to be measured or the replica signal.
In an additional aspect of the present invention, an input system for a continuously interpolated amplifier includes gm stages wherein the current from one of the transistors in each gm stage is diverted to an AC ground through a feedforward path.
REFERENCES:
patent: 4502020 (1985-02-01), Nelson et al.
patent: 4713628 (1987-12-01), Nelson
patent: 4994756 (1991-02-01), Brilka
patent: 5077541 (1991-12-01), Gilbert
patent: 5359293 (1994-10-01), Boksiner et al.
patent: 5444413 (1995-08-01), Kimura et al.
patent: 5473244 (1995-12-01), Libove et al.
patent: 5684431 (1997-11-01), Gilbert et al.
patent: 6204719 (2001-03-01), Gilbert
patent: 6335655 (2002-01-01), Yamamoto
patent: 6445248 (2002-09-01), Gilbert
Analog DeviceHigh Precision, Wide-Band RMS-to-DC Converter(AD637)Rev. E, 10 pages, 1999.
Analog Devices data sheets entitled “Dual, Low Noise, Wideband Variable Gain Amplifiers”, AD600/AD602, Rev. A, 20 pages, published Apr. 1992.
Analog Devices data sheets entitled “Low Level, True RMS-to-DC Converter”, AD636, Rev. A, 8 pages, published Sep. 1992.
Analog Devices data sheets for60 MHz, 2000 V/&mgr;S Monolithic Op Amp AD844, 12 pages, 1990.
Analog Devices Inc.
Marger & Johnson & McCollom, P.C.
Zweizig Jeffrey
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