Data Sheet HMC1169
Rev. 0 | Page 9 of 12
THEORY OF OPERATION
The HMC1169 voltage controlled oscillator is a free running
voltage controlled frequency source. The output frequency is
controlled by applying a variable tune voltage to the VTUNE port.
Because VTUNE is varied from the lowest to the highest allowed
voltage, the VCO output frequency increases from the lowest to
the highest operating frequency. This VCO output frequency
change with the applied VTUNE input results in the VCO
frequency sensitivity characteristic (MHz/V). The VCO
frequency sensitivity is not constant and varies across the
tunable range.
The HMC1169 VCO is specified to cover the minimum to
maximum frequencies specified in this data sheet over the entire
specified temperature range, including the VCO frequency drift
(MHz/°C). In addition, for low phase noise operation, drive the
VTUNE port from a low noise voltage source. Excessive noise
on the VTUNE port results in poor phase noise performance.
The tune port modulation bandwidth is typically greater than
10 MHz.
To achieve optimum VCO phase noise performance when using
the HMC1169, it is important to use a low noise power supply
for V
CC
biasing. Because the VCO output frequency changes
with small changes in the V
CC
bias voltage (pushing), noise on
the V
CC
bias pin results in increased phase noise. Take care to
use low noise regulators, otherwise, bias line noise may corrupt
the low phase noise output of the HMC1169.
Internally, the radio frequency (RF) output frequency is generated
from a doubler circuit. This generation results in an unwanted
low level output signal present at half the RFOUT frequency
(RFOUT/2). If necessary, this undesired spurious signal can be
further filtered on the customer application board using a filter.
The RFOUT/2 output signal is available directly at the RFOUT/2
port. The RFOUT/2 port commonly drives a phase-locked loop
(PLL) synthesizer for phase locking the HMC1169 output if
needed.
Lastly, the HMC1169 RFOUT port incorporates an internal
buffer amplifier to provide good output matching. The internal
buffer amplifier also isolates the VCO core from the output load
and minimizes the VCO frequency change with the changes to
the output load impedance (pulling).
