Data Sheet HMC8108
Rev. 0 | Page 15 of 18
APPLICATIONS INFORMATION
A typical lower sideband application circuit is shown in Figure 57.
The IF_Q output signal of the HMC8108 is connected to the
90° port of the hybrid coupler followed by a low-pass filter to
produce a lower sideband IF output signal. The LO input signal
passes through a voltage control oscillator (VCO) followed by
an optional buffer amplifier, a 2× frequency multiplier, and an
optional band-pass filter before entering the LO port of the
device. Band-pass filter and LO buffer are optional and depend
on the VCO specification and the LO input power requirement.
External capacitors of 0.6 pF, 1 nF, 10 nF, and 100 nF, and 5.6 nH
inductors are connected to the input voltage pin of the device.
The IF_I and IF_Q pins are dc-coupled and must not source or
sink more than 3 mA of current or device malfunction or possible
device failure may result. For applications not requiring
operation to dc, use an off chip dc blocking capacitor.
BIASING SEQUENCE
The HMC8108 uses amplifier and LO buffer stages. These active
stages use depletion mode, pseudomorphic high electron
mobility transfer (pHEMT) transistors.
To avoid transistor damage, follow these power-up bias
sequence steps:
1. Set the LNA_VG1, LNA_VG2, and BUFF_VG power
supplies to −2 V and the MIX_VG power supply to +1.4 V.
Do not turn on the power supplies.
2. Set the LNA_VD1, LNA_VD2, and BUFF_VD power
supplies to 3 V. Do not turn on the power supplies.
3. Set the VCTRL power supply to −1 V. Do not turn on the
power supply.
4. Turn on the power supplies in Step 1, Step 2, and Step 3 in
order.
5. Adjust the LNA_VG1, LNA_VG2, and BUFF_VG power
supplies between −2 V and 0 V to achieve an quiescent
current LNA_ID1, LNA_ID2, and BUFF_ID = 20 mA,
30 mA, and 40 mA, respectively.
6. Connect the signal generator to the RF and LO input.
7. Connect the 90° hybrid to the IF_I and IF_Q output. Note
that IF_Q is connected to the 90° port of the hybrid. Under
this condition, the lower sideband is selected.
8. Turn on the LO and RF input to see the output on the
spectrum analyzer.
To turn off the HMC8108, take the following steps:
1. Turn off the LO and RF signal source.
2. Turn off the LNA_VD1, LNA_VD2, and BUFF_VD power
supplies.
3. Turn off the LNA_VG1, LNA_VG2, BUFF_VG, MIX_VG,
and VCTRL power supplies. Refer to Figure 55 for the
HMC8108 lab bench setup.
15133-056
SPECTRUM
ANALYZER
RF INPUT
LO INPUT
POWER
SUPPLY
POWER
SUPPLY
POWER
SUPPLY
90°
90° HYBRID FOR
I/Q IF OUTPUT
0°
Figure 55. HMC8108 Lab Bench Setup
RESULTS
Figure 56 shows the expected results when testing the HMC8108
with the following operating conditions:
RF = −15 dBm at 9.44 GHz
LO = −5 dBm at 9.5 GHz
The on board IF_Q port is connected to the 90° port of the
hybrid.
The lower sideband is selected.
Note that hybrid, cable, and board loss were not deembedded.
0
–100
–80
–90
–70
–60
–50
–40
–30
–20
–10
CENTER 59.511MHz SPAN 16.3MHz1.63MHz/
(dBm)
15133-057
1
REF 0dBm ATT 5dB
RWB 6.25kHz
VBW 20kHz
SWT 420ms
MARKER 1 [T1]
–4.31dBm
60.00MHz
Figure 56. Test Results at IF = 60 MHz
