Dual-mode crystal oscillators with resonators excited on B and C modes

There is very attractive idea to use SC-cut resonators excited on B and C modes for frequency stabilization (in particular, for digital thermocompensation) but up to now these operating regimes are used very seldom. The cause consists in a difficulty to get stable excitation in wide temperature range. Due to development of original resonator excitation networks, of special geometry of piezoelement and due to original technology of its manufacture, we succeeded in developing of B and C modes in wide (-60...+85)°C temperature range. 70% yield of suitable units is attainable when resonators are exited on 10 MHz frequency using 1st mechanical harmonic. The requirements to a circuit of a dual-mode oscillator (that is oscillator capable of simultaneous exiting on two asynchronous frequencies) are presented. A lot of experiments have been involved to design double-mode crystal meeting the requirements assigned above. To avoid the dips of activity of the B-mode being inherent property of overton SC-cut crystals due to nonlinear interaction of the thickness modes the fundamental mode TD-cut (yxb1/23°25´/34°) crystal plate has been used here. Exploration of the modes activity behavior over a wide temperature range has shown that the motional resistance remains within (8-12) Ohms for C-mode and (50-65) Ohms for B-mode. Practical realization of the dual-modes oscillator in the form of a hybrid LCI is described. The dual-mode crystal oscillator parameters are: output frequency 10 MHz; supply voltage 5V; consumption current 5-7 mA; output levels TTL