# Frequency Multiplier Circuits

Frequency Tripler Using the CA3028 - Here is a simple frequency tripler using a CA3028 differential amplifier. The CA3028 has internal bias resistors for setting the differential amplifier's current at about 7 mA when connected as shown. With this current, the output level is about 0 dBm at 30 MHz with a 1v p-p, 10 MHz input. Other frequencies and multiplication factors are possible and the CA3028 may be replaced by discrete transistors.

Gyrator Circuit: The gyrator principle uses the effect that the value of input capacitance at the base of a transistor is effectively multiplied by the current gain of the transistor.

HCMOS Gates Make Frequency Multipliers

Q Multiplier

Two Diode Odd-Order Multiplier

CMOS Crystal Frequency Multiplier - Crystals usually operate at fundamental frequencies up to about 15 MHz. Whenever higher frequencies are required a frequency multiplier is placed after the crystal oscillator. The resulting output signal is then a whole multiple of the crystal frequency. Other frequency multipliers often use transistors, which produce harmonics due to their non-linearity. These are subsequently filtered from the signal. One way of doing this is to put a parallel L-C filter in the collector arm. This filter could then be tuned to three times the input frequency. A disadvantage is that such a circuit would quickly become quite substantial.

Frequency Multiplication or Frequency Synthesis - The block diagram of a frequency muliplier (or synthesizer) is shown in figure. In this circuit, a frequency divider is inserted between the output of the VCO and the phase comparator (PC) so that the loop signal to the PC is at frequency fOUT while the output of VCO is N fOUT. This output is a multiple of the input frequency as long as the loop is in lock. The desired amount of multiplication can be obtained by selecting a proper divide- by N network where N is an integer. Figure shows this function performed by a 7490 configured as a divide-by-4 circuit.

Frequency multiplier and wireless device incorporating same - A compact frequency multiplier can perform high-degree frequency multiplication and can be incorporated in a wireless device. The frequency multiplier includes an input terminal for inputting an input signal, a first resonant circuit resonating with the frequency ω of the input signal, a second resonant circuit and an idler circuit, which resonate with the frequency n·ω that is, n times the frequency of the input signal, a variable reactor such as a varactor diode, coupling-adjusting capacitors, a bias resistor, and an output terminal for outputting multiplied output signals.