CMX993 Datasheet, PDF(8/26 Page) CML Microcircuits – Programmable 30dB Output Gain Range

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CMX993 Datasheet, PDF (8/26 Pages) CML Microcircuits – Programmable 30dB Output Gain Range

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Quadrature Modulator

CMX993/CMX993W

4.2 Quadrature Modulator

Typical values for the quadrature modulator output circuits are shown in Figure 3/Table 3 and typical

configuration and values for the input circuits in Figure 4/4a and Table 4. Concerning Figure 3, the

transformer T1 should be located close to the CMX993/CMX993W and tracks from the MOP and MON

pins to T1 should be as close to equal in length as possible, preferably with a symmetrical layout. The

decoupling capacitor (C1) should be close to the centre tap of T1.

Note: Details of a simpler alternative output configuration are provided in an Application Note available

from www.cmlmicro.com.

MODQP

MODQN

MODIN

MODIP

Bandgap

MOP

MON

R3 AVDD T1 Output

R4 C1

VREF

BVREF

CMX993

CMX993W

Figure 3 Modulator Output External Components (30MHz to 1GHz)

10nF

Balun 4:1 (See Note 1)

1ÂµF

R3, R4

(See Note 2)

Note 1: For example TC4-14+ from mini circuits; for applications

between 200MHz and 1GHz or Coilcraft WBC4-1WL for

applications between 30MHz and 300MHz.

Note 2: The resistors R3 and R4 are optional. Fitting these with

110ï resistors will give a good broadband match

however will reduce output level available. For many

applications they will be unnecessary.

Table 3 Quadrature Modulator Output Components

The input configuration in Figure 4/4a is a possible solution for a single ended input with 0V dc bias. The

input amplifiers are used to translate the input to BVREF. In order to balance the small bias current drawn

by the modulator, the filter amplifiers are used to buffer BVREF. RC filters are used on the input to the

modulator to remove wideband noise generated by the differential amplifiers. The values of the resistors

and capacitors should be selected based on the bandwidths of the modulation. It is important to keep the

values of R6, R7, R8 and R9 the same so that small dc offsets generated by the modulator input bias

currents are matched, thereby providing the best carrier rejection. The networks R6/C1, R7/C2, R8/C3 and

R9/C4 should be placed close to the modulator input pins of the CMX993/CMX993W to ensure optimum

noise performance. It is important to note that due to small input bias currents, offset voltages and

component tolerances it is impractical to expect this type of input configuration to give ideal carrier

suppression. To achieve optimal carrier suppression it is recommended to have the ability to finely adjust

the dc offsets (see section 5.1.1).

ï£ 2013 CML Microsystems Plc

D/993/10

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