The trend for lightweight, low voltage battery operation in many of today’s consumer and communications equipment has driven the need for low voltage, high performance products for use in these systems. To meet these needs a new series of 5 × 7 mm surface-mount HCMOS crystal oscillators has been developed that operates from a 1.8 V supply and still maintains excellent phase noise and stability.
The R1800/R3800 series HCMOS clock oscillators permit the design of high frequency circuit boards that operate from a single 1.8 V DC supply, without the need for expensive and cumbersome special voltage supplies to feed more typical 3.3 and 5 V oscillators. In addition, the lower operating voltage curbs heat dissipation, increases reliability and extends the operating life of battery-powered equipment.
The new surface-mount oscillators are designed to provide clock waveforms needed for standard HCMOS circuits. The series also features low power consumption, low phase jitter, fixed frequency or Tristate operation, and a start up time of less than 5 ms. Tristate operation (R3800 series) is when the oscillation is halted so that automatic test equipment can inject special diagnostic waveforms. Tristating shuts down oscillation and reduces the power consumption to microwatts. The technique also provides a sleep mode for conserving battery life.
Of course, with the oscillators turned off there is the need for them to restart virtually instantly when required. The R1800/R3800 series oscillators guarantee that oscillations will take place regardless of how the supply voltage is applied. Oscillation begins within 5 ms of the DC supply voltage reaching rated level.
The new oscillators feature a frequency range of 850 kHz to 165 MHz and stability options from ±100 to ±25 ppm, as listed in Table 1. The phase noise performance is nearly as good as its big brother 3.3 and 5.0 V oscillators. Stability specifications include the worst-case effects of supply voltage and load variation. Typical aging is ±3 ppm during the first year and ±1 ppm/year in subsequent years. The oscillators are based on CMOS logic, guarantee 10 ps RMS max jitter and feature 45/55 typical waveform symmetry. Table 2 lists the oscillators’ electrical performance specifications.
The crystal resonator is the primary factor in maintaining good phase noise performance at the lower supply voltage. The R1800/R3800 oscillators utilize both fundamental mode and third-overtone mode resonators with specific attention given to the electrode geometry and surface finish of the quartz resonator to achieve superior phase stability. The lower supply voltage limits the options for accurate crystal drive control and wave shaping is more difficult. Figure 1 shows the phase noise performance of a 125 MHz R3800 1.8 V oscillator utilizing a third-overtone AT cut resonator.
Fig. 1 R3800 single sideband
phase noise performance at 125 MHz.
Typical application for this series of oscillators is for use in a surface-mount PCB that requires a standard HCMOS/TTL 1.8 V clock, including microprocessors and microcontrollers. The R1800/R3800 oscillators are hermetically sealed, operate from 0° to +70°C and meet typical Mil Std shock, vibration and humidity requirements for this type of device.