Mini Circuits has developed three LTCC thru lines that operate up to 20 GHz and are compatible with the most common LTCC filter footprints (0603, 0805 and 1206) and achieve excellent frequency responses to 20 GHz. The TPCW-203+, TPCG-203+, and TPCN-203+ thru lines give designers almost limitless options for drop-in replacement of the right filters wherever they are needed in the signal chain. The thru lines are available in 0603, 0805, and 1206 packages, respectively.
Built with rugged LTCC construction and wraparound terminations, these parts are well suited to the rigors of hand soldering when in the experimental phase, or reflow operations in production.
Preserving a thru line in a circuit where a filter might go allows the designer to observe system performance without any signal conditioning in order to determine precisely how much suppression is required from the desired filter. Traditionally, this was often accomplished by cutting the center conductor (50 ohm trace) on the circuit board and installing a section of copper ribbon to bridge the gap. Having the ability to insert a thru line block with a whole library of LTCC filters for drop-in replacement is a breakthrough, saving time and significantly simplifying the design and test processes.
These solutions can be used with LO Harmonic Filters. A thru line in lieu of the LO bandpass filter will help the designer determine the suppression necessary for the sub-harmonics and undesired harmonics since these signals will pass through the LO amplifier unfiltered. Additionally, the designer can examine the net effect on the desired harmonic level when passing unfiltered LO-related signals through the amplifier.
They can also be used in RF preselectors. Replacing the input BPF/preselector with a thru line and utilizing high-level interferers near the carrier enables the designer to examine the desensitization effect on the receiver LNA, and to ensure sufficient design margin is incorporated into the design when reinserting the LTCC BPF/preselector.
Another application is in IF Filters. The analysis of the IF BPF and the circuitry is perhaps the most complex of all the analyses that can be performed by inserting a thru line as a placeholder for a BPF. The previous signals such as the LO sub-harmonics/harmonics and receiver interferers that are now sufficiently suppressed by LTCC filters, are still incident upon the mixer at some level. The mixer has its own characteristic spur profile as well for any given range of RF and IF frequencies at a fixed LO frequency. Often shown graphically in the mixer spur chart, it is incumbent upon the designer to not only understand these spurs, but to suppress them adequately prior to amplification and digitization. The insertion of a thru line for the IF BPF combined with the utilization of a spectrum analyzer-based ATE setup to test for mixer spurs enables the designer to pinpoint the amount of spur suppression required.
Click here to learn more about the LTCC thru lines from Mini Circuits.
