Data Sheet HMC8038
Rev. A | Page 9 of 11
THEORY OF OPERATION
The HMC8038 requires a single-supply voltage applied to the
V
DD
pin. Bypassing capacitors are recommended on the supply
line to minimize RF coupling.
The HMC8038 is controlled via two digital control voltages
applied to the V
CTL
pin and the EN pin. A small bypassing
capacitor is recommended on these digital signal lines to
improve the RF signal isolation.
The HMC8038 is internally matched to 50 Ω at the RF input
port (RFC) and the RF output ports (RF1 and RF2); therefore,
no external matching components are required. The RFx pins
are dc-coupled, and dc blocking capacitors are required on the
RF lines. The design is bidirectional; the input and outputs are
interchangeable.
The ideal power-up sequence is as follows:
1. Power up GND.
2. Power up V
DD
.
3. Power up the digital control inputs. The relative order of
the logic control inputs are not important. Powering the digital
control inputs before the V
DD
supply can inadvertently
forward bias and damage ESD protection structures.
4. Power up the RF input.
With the EN pin is logic low, the HMC8038 has two operation
modes: on and off. Depending on the logic level applied to the
V
CTL
pin, one RF output port (for example, RF1) is set to on
mode, by which an insertion loss path is provided from the
input to the output, as the other RF output port (for example,
RF2) is set to off mode, by which the output is isolated from the
input. When the RF output port (RF1 or RF2) is in isolation
mode, internally terminate it to 50 Ω, and the port absorbs the
applied RF signal.
When the EN pin is logic high, the EN pin sets the HMC8038
switch to off mode. In off mode, both output ports are isolated
from the input, and the RFC port is open reflective.
Table 7. Switch Operation Mode
Digital Control Inputs Switch Mode
V
EN
V
CTL
RFC to RF1 RFC to RF2
0 0
Off mode. The RF1 port is isolated from the RFC port and
is internally terminated to a 50 Ω load to absorb the
applied RF signals.
On mode. A low insertion loss path from the RFC
port to the RF2 port.
0 1
On mode. A low insertion loss path from the RFC port to
the RF1 port.
Off mode. The RF2 port is isolated from the RFC port
and is internally terminated to a 50 Ω load to absorb
the applied RF signals.
1 X
1
All in off mode. Both the RF1 and RF2 ports are isolated from the RFC port, and the RFC port is reflective.
1
X stands for don’t care.
