LTC5599IUFPBF View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC5599IUFPBF' PDF : 42 Pages View PDF
LTC5599
Applications Information
The LTC5599 consists of I and Q input differential voltage-
to-current converters, I and Q upconverting mixers, an
RF output buffer and an LO quadrature phase generator.
An SPI bus addresses nine control registers, enabling
optimization of side-band suppression, LO leakage, and
adjustment of the modulator gain. See Table 1 for a sum-
mary of the writable registers and their default values.
A full map of all the registers in the LTC5599 is listed in
Table 10 and Table 11 in the Appendix.
Table 1. SPI Writable Registers and Default Register Values.
ADDRESS
0x00
0x01
0x02
0x03
0x04
0x05
0x06
0x07
0x08
DEFAULT
VALUE
0x2E
0x84
0x80
0x80
0x80
0x10
0x50
0x06
0x00
SETTING
490MHz
DG = –4
0mV
0mV
0dB
0°
OFF
OFF
NORMAL
REGISTER FUNCTION
LO Frequency Tuning
Gain
Offset I-Channel
Offset Q-Channel
I/Q Gain Ratio
I/Q Phase Balance
LO Port Matching Override
Temperature Correction
Override
Operating Mode
Without using the SPI the registers will use the default
values which may not result in the optimum side-band
suppression (SB). For example: for LO frequency from
about 400MHz to about 580MHz, the SB is about –45dBc;
from 380MHz to 400MHz and 580MHz to 630MHz it falls
to about –40dBc; from 350MHz to 380MHz and 630MHz
to 690MHz the SB falls to about –35dBc.
Aside of powering up the LTC5599, the register values can
be reset to the default values by setting SRESET = 1 (bit 3,
register 0x08). After about 50ns SRESET is automatically
set back to 0.
External I and Q baseband signals are applied to the dif-
ferential baseband input pins: BBPI, BBMI and BBPQ,
BBMQ. These voltage signals are converted to currents and
translated to RF frequency by means of double-balanced
upconverting mixers. The mixer outputs are combined at
the inputs of the RF output buffer, which also transforms
the output impedance to 50Ω. The center frequency of the
resulting RF signal is equal to the LO signal frequency.
The LO inputs drive a phase shifter which splits the LO
signal into in-phase and quadrature signals which drive the
upconverting mixers. In most applications, the LOL input
is driven by the LO source via a 39nH inductor, while the
LOC input is driven by the LO source via a 15pF capacitor.
This inductor and capacitor form a diplexer circuit tuned
to 200MHz. The RF output is single-ended and internally
50Ω matched across a wide RF frequency range from
0.6MHz to 6GHz with better than 10dB return loss using
C4 = 10nF. See Figure 13.
Baseband Interface
The baseband inputs (BBPI, BBMI, BBPQ, BBMQ) present
a differential input impedance of about 1.8kΩ, as depicted
in Figure 1. The baseband bandwidth depends on the
source impedance and the frequency setting (register
0x00). It is recommended to compensate the baseband
input impedance in the baseband lowpass filter design in
order to achieve best gain flatness vs baseband frequency.
The S-parameters for (each of) the baseband inputs are
given in Table 2 for various LO frequency and gain settings.
VCC = 3.3V
1 VCTRL
+
1.4V
EN
2.5mA
8 BBPI
9 BBMI
1kΩ 1kΩ
VCM = 1.4V
35Ω
10pF
40Ω
3pF
40Ω
3pF
5599 F01
Figure 1. Simplified Circuit Schematic of the Base Band Input
Interface (Only One Channel Is Shown).
For more information www.linear.com/LTC5599
5599f
19
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