A phase equalizer with a pair of ceramic resonators with different resonant frequencies than each other provides convex group delay time characteristics, which compensates for the concave group delay time characteristics of a ceramic filter. Thus, the flat group delay time characteristics in the combination of a ceramic filter and a phase equalizer is obtained, and excellent speech quality in analog signal transmission and/or excellent error rate in data transmission is obtained, while keeping excellent selectivity in a wireless communication system.
An IF crystal filter for a VHF receiver including: a crystal filter (18) having an input (22) and an output (24) a reactive impedance means (26) coupled across the crystal filter input and output for changing the selectivity characteristics of the crystal filter by a predetermined amount; and switching means (32) having a control input responsive to a control voltage, and coupled to said reactive impedance means for selectively shunting the reactive impedance means to ground, whereby to change the selectivity of the filter.
A plurality of quartz crystal resonators having different resonance frequencies are connected in parallel. A combined admittance of the resonators is measured. Equivalent circuit constants of all the resonators are obtained by a method of least squares from admittance characteristics. A change in the resonance frequency is measured and mass of a substance adsorbed to a piezoelectric transducer is calculated.
The present invention concerns a high impedance signal source driving a relatively low input impedance mechanical resonating device such as a ceramic filter having an input impedance which varies with frequency. The high impedance source is further loaded by a resonant circuit tuned to the center frequency of the mechanical resonating device. The skirts of the resonant tuned circuit decrease in impedance on both sides of the center frequency of interest substantially compensating for the change of circuit gain with frequency due to the change of input impedance with frequency of the ceramic filter.
An in-band group delay equalizer is formed in a simple circuit configuration so as to have a flat group delay characteristic over a wide frequency band without having a peak of group delay near each passband edge. The in-band group delay equalizer includes a plurality of convex group delay circuits. Each convex group delay circuit is formed of one hybrid coupler and two resonators connected to respective divided output ports of the hybrid coupler. The center frequencies of the respective convex group delay circuits are set to be different from each other so that the overall group delay characteristic of the in-band group delay equalizer becomes flat. The bandwidth and the group delay can be easily adjusted. A distortion compensation amplifier with very low distortion can be realized using such an in-band group delay equalizer.
An electric filter comprises a plurality of thin film bulk acoustic resonants (10, 11) arranged in series and in parallel which have electrodes (24, 25) of different working area (L) and optionally a piezoelectric layer (23) of different thickness (T).
