HMC8108LC5TR-R5 datasheet(15/18 Pages) AD

15 / 18 page

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:

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.

Set the LNA_VD1, LNA_VD2, and BUFF_VD power

supplies to 3 V. Do not turn on the power supplies.

Set the VCTRL power supply to −1 V. Do not turn on the

power supply.

Turn on the power supplies in Step 1, Step 2, and Step 3 in

order.

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.

Connect the signal generator to the RF and LO input.

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.

Turn on the LO and RF input to see the output on the

spectrum analyzer.

To turn off the HMC8108, take the following steps:

Turn off the LO and RF signal source.

Turn off the LNA_VD1, LNA_VD2, and BUFF_VD power

supplies.

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.

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.

–100

–80

–90

–70

–60

–50

–40

–30

–20

–10

CENTER 59.511MHz

SPAN 16.3MHz

1.63MHz/

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

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