adl5386 Analog Devices, Inc., adl5386 Datasheet - Page 19

• Manufacturer Part Number: adl5386
• Description: 50 Mhz To 2200 Mhz Quadrature Modulator With Integrated Detector And Vva
• Manufacturer: Analog Devices, Inc.

CIRCUIT DESCRIPTION
OVERVIEW
The ADL5386 consists of three sections: a quadrature modulator, a
logarithmic detector, and a voltage variable attenuator (VVA).
The modulator section contains the circuitry for the following
functions:
•
•
•
•
•
The detector section contains the logarithmic detector and
amplifiers interfacing to the VSET input and VDET output.
The variable attenuator section consists of a PI network of
PHEMTs and resistors implemented on a GaAs die separate
from the silicon die where the rest of the circuits reside. A
detailed block diagram of the device is shown in Figure 39.
QUADRATURE MODULATOR SECTION
The LO interface generates two LO signals at 90° of phase
difference to drive two mixers in quadrature. Baseband signals
are converted into currents by the V-to-I converters that feed
into the two mixers. The outputs of the mixers are combined in
the differential-to-single-ended amplifier, which provides a 50 Ω
output interface. Reference currents to each section are generated
by the bias circuit. A detailed description of each section follows.
LO Interface
The LO interface consists of a buffer amplifier followed by a
pair of frequency dividers that generate two carriers at half the
input frequency and in quadrature with each other. Each carrier
is then amplified and amplitude-limited to drive the double-
balanced mixers.
Local oscillator (LO) interface
Baseband voltage-to-current (V-to-I) converter
Mixers
Differential-to-single-ended (D-to-S) amplifier
Temperature sensor and bias circuit
QBBN
QBBP
IBBP
IBBN
LOIN
LOIP
30
25
26
33
34
29
TEMPERATURE
38 37
SENSOR
TEMP
VPOS
QUADRATURE
8
SPLITTER
36
PHASE
35
INLO
1
INHI
2
23
VPOS
22 21
Figure 39. Block Diagram
DETECTOR
Rev. 0 | Page 19 of 36
LOG
IQ MOD
ENBL
TADJ
BIAS
24
39
ADL5386
5
11
V-to-I Converter
The differential baseband input voltages that are applied to the
baseband input pins are fed to a pair of common-emitter, voltage-
to-current converters. The output currents then modulate the
two half-frequency LO carriers in the mixer stage.
Mixers
The ADL5386 has two double-balanced mixers: one for the
in-phase channel (I channel) and one for the quadrature channel
(Q channel). These mixers are based on the Gilbert cell design
of four cross-connected transistors. The output currents from
the two mixers are summed together in the resistor-inductor
loads in the D-to-S amplifier.
D-to-S Amplifier
The output D-to-S amplifier consists of two emitter followers
driving a totem-pole output stage. Output impedance is established
by the emitter resistors in the output transistors. The output of
this stage connects to the output (VOUT) pin.
Bias Circuits
A band gap based bias circuit provides proportional-to-absolute
temperature as well as temperature stable reference currents for
the different circuits in the modulator section. The ENBL input
controls the operation of this bias circuit. When ENBL is pulled
to a low level, the bias references are turned off, and the whole
modulator section is turned off as a result. A voltage that is
proportional to the absolute temperature of the circuit is also
available at the TEMP pin.
A separator bias circuit provides the reference currents as well
as the reference voltages for the detector and voltage variable
attenuator sections. This bias circuit can also be disabled by
pulling the TADJ pin high, which in turn shuts down the
detector section.
13
MODOUT
15
COMM
10
16 18
19 27
ATTI
12
15dB
28
I
31
I
V
32
NC
9
V
40
17
14
20
6
4
3
7
ATTCM
ATTCM
ATTO
VREF
VDET/VCTL
CLPF
VSET
ADL5386