Wave transmission lines and networks – Coupling networks – Delay lines including a lumped parameter
Reexamination Certificate
2001-09-20
2003-07-01
Tokar, Michael (Department: 2819)
Wave transmission lines and networks
Coupling networks
Delay lines including a lumped parameter
C333S032000, C333S138000, C333S164000, C327S252000, C327S237000
Reexamination Certificate
active
06587017
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and/or architecture for calibrating phase-shift networks generally and, more particularly, to high frequency or narrowband signal processing.
BACKGROUND OF THE INVENTION
Referring to
FIGS. 1
a
and
1
b
, a pair of high-frequency (or narrowband) signal processing applications
10
utilizing phase-shift networks are shown. The signal processing application
10
of
FIG. 1
a
synthesizes (or generates) two signals with a specific, 90 degree (i.e., quadrature) phase relationship to each other. A narrowband input RF (i.e., a single sinusoid) is fed into the phase shift network
10
of
FIG. 1
a
, which then outputs two desired quadrature signals of equal amplitude and 90 degree phase relationship. A second input to the phase-shift network
10
of
FIG. 1
a
is coupled to ground.
The signal processing application
10
of
FIG. 1
b
is an image-rejection mixer (found in cellular phones, wireless local-area networks, television tuners, etc.). An incoming radio-frequency (RF) signal is fed into two separate mixers, one driven by a sine wave, and the other driven by a cosine wave. The filter is typically implemented as a low pass filter (or as no filter at all). The output of each mixer has the classic problem of undesired image-band conversion, where not only the desired signal (i.e.,
1
and
4
) is converted into the mixer output, but also any signal at the associated image frequency (i.e.,
2
and
3
). The phase-shift network
10
of
FIG. 1
b
combines the outputs of both mixers, due to the 90 degree phase relationship of the undesired image and the desired signal, the phase-shift network
10
of
FIG. 1
b
can then separate the two signals, leaving only the desired signal.
In the phase-shift networks
10
, the critical performance metric of the phase-shift network is in gain/phase matching. How well balanced the outputs of
FIG. 1
a
, or how well separated the undesired image of
FIG. 1
b
, is determined by how accurately the phase-shift network
10
can achieve the desired 90 degree phase relationship.
Referring to
FIG. 2
a
, a conventional resistor-capacitor (RC) ladder network method for implementing a phase-shift network
20
is shown. Since the PSN
20
is implemented using only resistors and capacitors, integration in standard silicon is amenable. However, such PSN architectures have the drawback of only achieving precision 90 degree phase shifts at one specific frequency (i.e., &ohgr;=1/(R*C)). Furthermore, typical applications only allow for a phase shift error of approximately 1 degree (i.e., the PSN must shift somewhere between 89 and 91 degrees). Thus, any on-chip variability will substantially limit the effectiveness of such a PSN. For example, a 500 MHz PSN meeting a 1 degree phase error specification would require on-chip resistors and capacitors accurate to better than 0.5%. Laser trimming can achieve the exceptionally high level of accuracy. However, laser trimming is expensive and difficult to implement (i.e.; inappropriate for high-volume consumer applications such as cellular phones).
Referring to
FIG. 2
b
, a conventional cascaded multiple phase-shift network circuit
30
is shown. The cascaded PSN circuit
30
provides a range of frequencies over which accurate phase shift occurs. The circuit
30
allows for on-chip resistor and capacitor tolerances. Therefore, the circuit
30
is insensitive to on-chip variability. However, every additional stage of phase shift results in signal attenuation (since the circuit
30
is passive), as well as additional noise from the resistors. Thus, a designer is strongly motivated to utilize as few stages of phase-shift as possible, while meeting the performance requirements.
SUMMARY OF THE INVENTION
The present invention concerns an apparatus comprising a first calibration circuit and a phase shift network stage. The first calibration circuit may be configured to generate a control signal. The phase shift network stage may comprise one or more tunable phase shift elements and be configured to provide a tunable impedance. The phase shift network stage may be tuned in response to the control signal and a conductance of the tunable phase shift elements.
The objects, features and advantages of the present invention include providing a method and/or architecture for calibrating phase-shift networks that may (i) be automatically calibrated, (ii) be implemented without requiring laser trim, (iii) implement fewer stages and/or (iv) be implemented without other costly per-part manufacturing adjustments.
REFERENCES:
patent: 4532518 (1985-07-01), Gaglione et al.
patent: 4599585 (1986-07-01), Vorhaus et al.
patent: 4682128 (1987-07-01), Sproul et al.
patent: 4733203 (1988-03-01), Ayasli
patent: 4961062 (1990-10-01), Wendler
patent: 4978931 (1990-12-01), Carp et al.
patent: 5136265 (1992-08-01), Pritchett
patent: 5237629 (1993-08-01), Hietala et al.
patent: 6137377 (2000-10-01), Wallace et al.
“Integrated Continuous-Time Balanced Filters for 16-b DSP Interfaces”, By Anna M. Durham and William Redman-White, IEEE Journal of Solid-State Circuits, vol. 28, No. 7, Jul. 1993, pp. 835-839.
Lynn Lapoe E.
Sheng Samuel W.
LSI Logic Corporation
Mai Lam T.
Maiorana P.C. Christopher P.
Tokar Michael
LandOfFree
Method and apparatus for calibrated phase-shift networks does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for calibrated phase-shift networks, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for calibrated phase-shift networks will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3053480