Filter having resonators coupled by a saw filter and a duplex filter formed therefrom

• US 5,467,065 A
• Filed: 02/28/1994
• Issued: 11/14/1995
• Est. Priority Date: 03/03/1993
• Status: Expired due to Fees

• Current Assignee: Pulse Finland Oy (Yageo Corporation)
• Original Assignee: Pulse Finland Oy (Yageo Corporation)
• Inventors: Jantunen, Heli, Turunen, Aimo
• Primary Examiner(s): LEE, BENNY T
• Application Number:
  US08/202,901
• Time in Patent Office: 624 Days
• Field of Search: 333/126, 333/129, 333/132-135, 333/193, 333/202, 370/38, 370/123
• US Class Current: 333/132
• CPC Class Codes: H01P 1/203 Strip line filters
• CPC Class Codes: H01P 1/2039 Galvanic coupling between Input/Output

Abstract

A filter, particularly suitable for radio frequency applications comprises a first filter which, in turn, comprises at least a pair of intercoupled resonators (RES1, RES2), and a SAW filter (SAW) which is coupled between the two intercoupled resonators so that a signal input to the filter at its input (IN) is coupled through the SAW filter to provide an output signal at its output (OUT). This provides a filter with all the advantages of a SAW filter, but with the ability to withstand the high power requirements of radio frequency applications. If three or more resonators are present in the first filter, then an amplifier can also be integrated in the filter. The SAW filter (and the amplifier if present) are inductively or capacitively coupled to the resonators depending upon the type of filter that is required.

Claims

1. A filter having an input and an output for providing an output signal at the output from an input signal applied at the input, the output signal having a frequency in a frequency range, the filter comprising:

a first filter comprising at least a pair of intercoupled resonators; and

a SAW filter coupled between the pair of intercoupled resonators to provide intercoupling therebetween, whereby the input is coupled to the output through the SAW filter to provide the output signal.

2. A filter as claimed in claim 1 characterised in that the SAW filter is capacitively coupled to each of the pair of resonators.

3. A filter as claimed in claim 1, characterised in that the SAW filter is inductively coupled to each of the resonators of the pair of resonators.

4. A filter having an input and an output, the filter providing an output signal at the output from an input signal input at the applied, the output signal having a frequency in a predetermined frequency range, the filter comprising:

first, second and third resonators;

a SAW filter coupled between the second and third resonators; and

an amplifier coupled between the first and second resonators, and also coupled to the SAW filter, such that the input signal is coupled to the output through the amplifier and the SAW filter to provide an amplified output signal.

5. A radio transceiver comprising:

an antenna;

a receiver section;

a transmitter section; and

a duplex filter coupling the antenna to both the receiver and transmitter sections, the duplex filter comprising a receiver branch filter with an output coupled to the receiver section and with an input coupled to the antenna for filtering a received signal coupled from the antenna, and a transmitter branch filter with an input coupled to the transmitter section and with an output coupled the antenna for filtering a signal coupled from the transmitter section to the antenna, at least one of the receiver branch filter and transmitter branch filter respectively comprising at least one filter, the at least one filter comprising;

a first filter comprising at least a pair of intercoupled resonators; and

a SAW filter coupled between the pair of intercoupled resonators to provide the intercoupling, whereby the input is coupled to the output through the SAW filter to provide the output signal.

6. A radio transceiver as claimed in claim 5 wherein the one filter is in the receiver branch of the duplex filter.