Trimmer capacitors serve an invaluable circuit function, or a necessary evil, depending upon an engineer's viewpoint. Although the presence of a trimmer in a circuit implies a need to tune, some applications, such as filters and oscillators, require precise tuning to achieve a desired operating frequency. Of course, most engineers will gripe about the size that a trimmer adds to a printed-circuit board (PCB)that is, until they have tried the new J Series of ceramic chip capacitors from Voltronics Corp. (Denville, NJ). With capacitance ranges as wide as 10 to 120 pF in a single component, and self-resonant frequencies reaching 6 GHz for a wide range of applications, engineers no longer have to sacrifice PCB space for the capacitance tuning function.

The J Series ceramic chip capacitors (see figure) are ideal for surface-mount and PCB applications. With seven different package styles in the series, engineers can easily trade off size for tuning range: the largest of the J Series trimmers provide the widest capacitance tuning ranges. The JB series, which measures a "whopping" 0.236 0.236 0.189 in. (6 6 4.8 mm), offer the greatest available capacitance tuning range, with models JB900 and JB1200 providing adjustable ranges of 9 to 90 pF and 10 to 120 pF, respectively. The self-resonant frequencies (SRFs) for these trimmers, which are specified at the highest available capacitance setting, are 200 and 170 MHz, respectively. Other members of the JB series include models JB023, with a capacitance tuning range of 1.25 to 2.3 pF and SRF of 1.4 GHz, and JB050, with a capacitance tuning range of 1.5 to 5.0 pF and SRF of 0.9 GHz.

For engineers needed only a few picofarads of adjustable capacitance, the tiny JN series trimmer capacitors measure only 0.067 0.059 0.035 in (1.7 1.5 0.9 mm) but provide adjustable capacitance from 1.5 to 4.0 pF for the model JN040 and from 3 to 8 pF for the model JN080. The SRFs for the JN040 and JN080specified at their maximum capacitance settingsare 2.7 and 1.8 GHz, respectively. The JN series trimmers, and the J Series components in general, exhibit minimal changes in capacitance as a function of changing temperature, as evidenced by temperature coefficient of 0 500 PPM/C for the JN040 and 750 500 PPM/C for the JN080, across an operating temperature range of 25 to +85C.

For particularly critical mounting requirements, the JZ and JR series feature no exposed metal mechanism underneath the ceramic chip packaging. The JZ series measures 0.177 0.126 0.059 in. (4.5 3.2 1.5 mm). Capacitance tuning ranges in the series include 1.5 to 3.0 pF (model JZ030), 2 to 6 pF (model JZ060), 3 to 8 pF (model JZ080), 5.5 to 30 pF (model JZ300), and 8 to 40 pF (model JZ400). Minimum Q ranges from 500 to 1500 at 1 MHz. The temperature coefficients are as tight as 0 200 PPM/C for the JZ030.

The J Series ceramic chip capacitors are available in tape-and-reel format for use with automated manufacturing equipment. Voltronics Corp., 100 Ford Rd., Denville, NJ 07834; (973) 586- 8585, FAX: (973) 586-3404, e-mail: info@voltronicscorp.com, Internet: www.voltronicscorp.com.