Delay line filter

Details Delay line filter Delay line filter

2000-06-14

2001-11-13

Lee, Benny T. (Department: 2817)

Wave transmission lines and networks

Plural channel systems

Having branched circuits

C333S140000, C333S167000, C333S175000, C333S185000

Reexamination Certificate

active

06317013

ABSTRACT:

FIELD OF THE INVENTION
The present invention is directed generally to systems and methods for filtering and/or delaying transmission signals, and, more particularly, to systems and methods for providing integrated filters with a flat delay response.
DESCRIPTION OF THE RELATED ART
The popularity of cellular phones and other wireless communication equipment over the last several years has resulted in the need to obtain greater utilization from the existing frequency spectrum while at the same time reducing the cost of technology used to operate at high frequencies. An important component of any cellular system is the high power amplifier which amplifies signals associated with the cellular system. A particular effective high power amplifier is a feed forward design which typically includes one or more delay lines along a main path and one or more delay lines along a secondary feed forward path.
FIG. 1
shows an exemplary feed forward high power amplifier
1
. In this embodiment, the main path includes a hybrid splitter
2
, a phase and amplitude adjustment
3
, a main amplifier
4
, an output coupler
5
, a delay line
6
, and an error injection coupler
7
, feeding output
13
. The secondary path in the embodiment shown in
FIG. 1
includes a delay line
8
, a hybrid combiner
9
, phase and amplitude adjustment circuits
10
,
11
, and an error amplifier
12
. The high power amplifier shown in
FIG. 1
is suitable for use as a multi-carrier power amplifier.
The delay lines ideally have a uniform, temperature stable, and fixed amount of insertion delay and constant phase over a predetermined frequency range. Conventionally, the delay lines
6
along the main path is implemented using multi-path delay equalization cavity filters. The multi-path delay equalization cavity filters are configured to utilize cross coupling techniques available due to the greater isolation of cavity filters to minimize delay variations across the passband while handling very high levels of power, e.g., in excess of 1,000 watts for most designs, and over 2,000 watts on a custom basis, even for small cavity diameters. Examples of this type of delay line are available from the assignee of the present application as a standard product line. Filters of this type are typically large measuring from around 15 in
2
to more than 40 in
2
.
Other cavity filter delay lines are, for example, shown in U.S. Pat. Nos. 4,622,523 and 3,699,480. Again, these cavity filters are typically used on the main path of the power amplifier shown in FIG.
1
.
On the secondary “feed forward” path, the conventional implementation of the delay lines (e.g., delay line
8
in
FIG. 1
) is a coiled coaxial cable or micro-strip printed on a high dielectric material. Examples of devices falling within this category are shown in U.S. Pat. Nos. 4,409,568, 5,252,934, and 4,218,664 and in conventional components such as Murata LDH33, LDH36, and LDH46 series delay lines. However, conventional printed micro-strip delay lines are disadvantageous in that there is coupling between the various turns across the high dielectric material and a high insertion loss. Coaxial cable type delay lines have little cross coupling but still are characterized by high insertion loss, and require a large amount of area to implement. Accordingly, a suitable secondary delay circuit is not now available conventionally.
Various attempts have been made to achieve delay equalization using active components to shift various delay response curves and add them together. For example, U.S. Pat. No. 3,942,118, issued to Haruo Shiki suggests cascading together a first frequency converter, a first filter, a first series of all-frequency pass filters having successively rising resonant frequencies and successively lowering Q-values (first delay equalizer), a second frequency converter, with a second filter circuit, a local oscillator, and a second series of all-frequency pass filters having successively rising resonant frequencies and successively lowering Q-values (second delay equalizer). However, this circuit has the disadvantage in that there are large insertion losses, large volume resulting from the large number of components, and temperature instability due to the number of active components. Other attempts at active delay equalization, such as, U.S. Pat. No. 4,491,808, suffer from similar problems.
In 1964, Dr. S. B. Cohn proposed using a four port coupler or a three port circulator to achieve equalization of non-linear phase angle or time delay characteristics of other components. See, for example, U.S. Pat. No. 3,277,403, herein incorporated by reference. U.S. Pat. Nos. 4,197,514 and 4,988,962 cite examples of Dr. Cohn's earlier work as prior art in the background portions of the respective specifications. Over the years, there has been several attempts at implementing the structures suggested by S. B. Cohn through the use of bulky, costly, and large devices such as that shown by the above mentioned U.S. Pat. No. 3,699,480 showing a cavity filter circulator coupled to an impedance circuit. Heretofore, none of these devices has been practical for low cost applications such as the secondary delay line in the multi-carrier power amplifiers discussed in connection with FIG.
1
.
Attempts to configure miniaturized implementations using the same designs employed in delay equalized cavity filters have thus far proved unsuccessful due to the cross coupling between the various lumped components of the filter. Heretofore, it was not thought possible to implement such a filter using discrete components.
The lack of shielding in the lumped elements necessarily influences and has a deleterious effect on the overall operation of delay equalization implementations using lumped elements. Conventionally, it was thought that cross coupling in this circuit would result in a device which is nonfunctional for its intended purpose. In the secondary loop, heretofore, it has been thought to be impossible to construct a flat delay response using lumped components configured in a miniaturized configuration because of the numerous stray inductances and the lack of shielding between resonators.
Because of these problems, the present state of the art is to use a coaxial delay line in the secondary path of the feed forward power amplifier. However, the coaxial delay line in the secondary path has many of the problems discussed above and thus is not satisfactory. Accordingly, the present invention seeks to take an altogether new approach to equalizing the delay across the passband using lumped discrete components. The present invention further seeks to provide improved high and low power delay lines in the main and secondary paths, respectively.
SUMMARY OF THE INVENTION
The goal of one or more aspects of the invention is to define a lumped element delay line which has a flat delay characteristic over the passband in a similar manner to how the cavity delay line has a relatively flat delay characteristic over the passband. The present invention utilizes a new configuration for lumped elements previously thought not to be practical in a miniaturized structure. The new architecture utilizes conventional theories to provide a highly improved structure for delay equalization using lumped components to form a flat delay response. This is particularly useful in the secondary feed forward path of the linear amplifier.
One or more aspects of the present invention may solve one or more of the above problems and/or provide improved techniques for implementing delay lines using lumped components.
In one aspect of the invention, a miniaturized delay line assembly is configured using lumped components comprising a miniaturized 3 dB quadrature hybrid coupler (having resonators using lumped components) coupled to two ports and connected in series with a discrete implementation of a band pass filter.
In another aspect of the invention, the lumped components are tuned and mounted in a metal canister prior to shipping to a customer in order to provide the proper equalization. Proper equalization is difficult to

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