Complete Dual-Band

Quadrature Transmitters

______________________________________________________________________________________

11

Detailed Description

The MAX2360 complete quadrature transmitter accepts

differential I/Q baseband inputs with external common-

mode bias. A modulator upconverts this to IF frequency

in the 120MHz to 300MHz range. A gain control voltage

pin (VGC) controls the gain of both the IF and RF VGAs

simultaneously to achieve best noise and linearity per-

formance. The IF signal is brought off-chip for filtering,

then fed to a single sideband upconverter followed by

the RF VGA and PA driver. The RF upconverter requires

an external VCO for operation. The IF PLL, RF PLL, and

operating mode can be programmed by an SPI/QSPI/

MICROWIRE-compatible 3-wire interface.

The following sections describe each block in the

MAX2360 Functional Diagram.

I/Q Modulator

Differential in-phase (I) and quadrature-phase (Q) input

pins are designed to be DC-coupled and biased with the

baseband output from a digital-to-analog converter

current-drive capability of 6µA. Common-mode voltage

Typically, I and Q will be driven differentially with a

bit in the configuration register. The IF VCO output is fed

into a divide-by-two/quadrature generator block to derive

quadrature components to drive the IQ modulator. The

output of the modulator is fed into the VGA.

IF VCOs

There are two VCOs to support high IF and low IF appli-

cations. The VCOs oscillate at twice the desired IF fre-

quency. Oscillation frequency is determined by external

tank components (see Applications Information).

Typical phase-noise performance for the tank is as

shown in Table 1. The high-band and low-band VCOs

can be selected independently of the IF port being

used.

IFLO Output Buffer

IFLO provides a buffered LO output when BUF_EN is 1.

The IFLO output frequency is equal to the VCO fre-

quency when BUF_DIV is 0, and half the VCO frequen-

cy when BUF_DIV is 1. The output power is -6dBm. This

output is intended for applications where the receive IF

is the same frequency as the transmit IF.

IF/RF PLL

The IF/RF PLL uses a charge-pump output to drive a

loop filter. The loop filter will typically be a passive sec-

ond-order lead lag filter. Outside the filter’s bandwidth,

phase noise will be determined by the tank compo-

nents. The two components that contribute most signifi-

cantly to phase noise are the inductor and varactor.

Use high-Q inductors and varactors to maximize equiv-

alent parallel resistance. The IF_TURBO_CHARGE and

the RF_TURBO_CHARGE bits in the CONFIG register

can be set to 1 to enable turbo mode. Turbo mode pro-

vides maximum charge-pump current during frequency

acquisition. Turbo mode is disabled after the second

transition from phase lead to phase lag or from phase

lag to phase lead. Turbo mode is also disabled after

frequency acquisition is achieved. When turbo mode is

disabled, charge-pump current will return to the pro-

grammed levels as set by ICP and RCP bits in the

CONFIG register (Table 4).

IF VGA

The IF VGA allows varying an IF output level that is con-

trolled by the VGC. The voltage range on VGC of 0.5V

to 2.6V. provide a gain-control range of 85dB. There

are two differential IF output ports from the VGA.

IFOUTL+/IFOUTL- are optimized for low IF operation

(120MHz to 235MHz) for IFOUTH+/IFOUTH- support

high IF operation (120MHz to 300MHz). IFOUTL ports

support direct VCO FM modulation. The differential IF

output port has an output impedance of 600

Ω when

Single Sideband Mixer

The RF transmit mixer uses a single sideband architec-

ture to eliminate an off-chip RF filter. The single sideband

mixer has IF input stages that correspond to IF output

ports of the VGA. The mixer is followed by the RF VGA.

The RF VGA is controlled by the same VGC pin as the IF

VGA to provide optimum linearity and noise perfor-

mance. The total power control range is >100dB.

PA Driver

The MAX2360 includes three power-amplifier (PA) dri-

vers. Each is optimized for the desired operating fre-

quency. RFL is optimized for cellular-band operation.

Table 1. Typical VCO Phase Noise

(IF = 130.38MHz)

30

12.5

1

OFFSET (kHz)

PHASE NOISE (dBc)

-80

-105

-111

900

120

-121

-128