MAX2426

________________General Description

The MAX2424/MAX2426 evaluation kits (EV kits) simplify
evaluation of the MAX2424/MAX2426 900MHz image-
reject transceiver.

The EV kits provide 50

SMA connectors for all RF

inputs and outputs. A varactor-based tank circuit is pro-
vided for the MAX2424/MAX2426 VCO and can be tuned
by a potentiometer or external voltage. The VCO can be
overdriven by an external source, if desired. (See exter-
nal LO input under

Adjustments and Control section).

Switches are provided to control power-management
features.

____________________________Features

SMA Ports for Testing Transmit and Receive

Paths

SMA Port for Prescaler Output

Switches Included to Control Power-Management
Features

VCO Frequency and Receiver Adjustable via
On-Board Potentiometers or External Inputs

Fully Assembled and Tested

Evaluate: MAX2424/MAX2426

MAX2424/MAX2426 Evaluation Kits

________________________________________________________________

Maxim Integrated Products

QTY

DESCRIPTION

C1, C4, C5, C7,

C9, C10, C12,

C15, C19,
C22C24,

C28, C32

C8, C11, C13,

C29, C30, C31

C16

1000pF ceramic capacitor

C17, C18

2.0pF ceramic capacitor
(0603) (MAX2424)

Dual-varactor diode Alpha SMV1299-004

0.01µF ceramic capacitors

47pF ceramic capacitors

DESIGNATION

10µF, ±10%, 10V tantalum capacitors
AVX TAJB106K010 or
Sprague 2930106X90010B

______________________________________________________________Component List

PART

MAX2424

EVKIT

-40°C to +85°C

TEMP. RANGE

IC PACKAGE

28 SSOP

DESIGNATION QTY

DESCRIPTION

L5, L7

Not installed

12nH inductor
Coilcraft 0805CS-120XMBC

18nH inductor
Coilcraft 0805CS-180XMBC

82nH inductor
Coilcraft 0805CS-820XKBC

R2, R3

10k

potentiometers

R4, R5

, 5% resistors

, 5% resistors (0402) (MAX2424)

47k

, 5% resistor

R9, R14R17

10k

, 5% resistors

R11, R21

Not installed

R12

301

, 1% resistor

R18, R20

49.9

, 1% resistors

_______________Ordering Information

MAX2426

EVKIT

-40°C to +85°C

28 SSOP

C2, C3

C6, C14

0.1µF ceramic capacitors

100nH inductor
Coilcraft 0805CS-101XKBC

C27, C33

Not installed

R10, R13

10k

, 5% resistors

R19

resistor

6.8nH, 5% inductor (MAX2424)
Coilcraft 0805HS-060TJBC

19-1350 Rev 2; 2/99

C26

4.0pF ceramic capacitor
(0603) (MAX2426)

3.3nH, 5% inductor (MAX2426)
Coilcraft 0805HS-030TJBC

22nH inductor
Coilcraft 0805CS-220XMBC

R6, R7

, 5% resistors (0402) (MAX2426)

For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.

8.2nH inductor
Coilcraft 0805CS-080XMBC

Component List continues on next page.

Note: All resistors and capacitors have a 0805 footprint, unless otherwise noted.

8.0pF ceramic capacitors
(0603) (MAX2426)

3.3pF ceramic capacitors
(0603) (MAX2424)

_________________________Quick Start

The MAX2424/MAX2426 EV kits are fully assembled
and factory tested.

Do not turn on the DC power and

signal sources until all connections are made.

The

following discussion is based on the MAX2424 with a
receive IF frequency of 10.7MHz, high-side LO injection
and 1MHz transmit input with a 915MHz LO frequency.

Test Equipment Required

RF-signal generator capable of generating frequen-
cies up to 1GHz

Spectrum analyzer with frequency range at least to
3GHz, such as the HP8561

Two power supplies capable of up to +5.5V output at
100mA

Connections and Signal Conditions

1) Verify that all shunts are installed across jumpers

JU2, JU4, JU7, and JU8.

2) Verify that switch positions 1 through 5 on SW1 are

set at the "logic 0" position.

3) Set a power supply to 3.3V and set the current limit

to 100mA.

4) Connect the power supply to the VEXT and GND

terminals on the EV kit.

5) Set a power supply to 2.3V and set the current limit

to 100mA.

6) Connect the power supply to the BPSK and GND

terminals on the EV kit.

7) For testing the receive path, set the signal source

frequency to 915MHz (RF) and the power level to
-35dBm. For testing the transmit path, set the signal
source frequency to 1MHz and the signal level to
250mVp-p. Note that TXIN is terminated with a 50

load.

Analysis

1) Turn on the on-chip oscillator by setting switch

VCOON to "logic 1." To observe the VCO frequen-
cy, set switch DIV 1 to "logic 1" (disabling the
prescaler and enabling the buffer amplifier) and
connect an SMA cable from the spectrum analyzer
to the PREOUT port. Set the VCO frequency to
925.7MHz by adjusting VCOADJ (R3).

2) The receive conversion gain can be evaluated by

setting switch RXON to "logic 1," applying a
915MHz signal to the RXIN port, and observing the
RXOUT port at 10.7MHz with the spectrum analyz-
er. The gain of the LNA in the receiver path can be
adjusted by varying R2.

Note:

R12 and R18 are used as a resistive match-

ing network to present an optimum 330

imped-

ance to the RXOUT pin. This network results in a
14.2dB loss in the receiver path. Therefore, 14.2dB
must be added to the power level observed on the
spectrum analyzer to obtain the true receive output
power. For example, with LNAGAIN set at V

and

the receive input level set at -35dBm, the receive
output observed on the spectrum analyzer is
approximately -27.2dBm. The true receive conver-
sion gain is -27.2 - (-35) + 14.2 = 22dB.

If desired, pads for C8, R18, C30, R12, L5, and
C20 can be used to build a custom reactive-
matching network.

Evaluate: MAX2424/MAX2426

MAX2424/MAX2426 Evaluation Kits

_______________________________________________________________________________________

SUPPLIER*

PHONE

FAX

Alpha Industries

(617) 935-5150

(617) 933-2359

Coilcraft

(847) 639-6400

(847) 639-1469

Sprague

(603) 224-1961

(603) 224-1430

_______Component List (continued)

______________Component Suppliers

AVX

(803) 946-0690

(803) 626-3123

Please indicate that you are using the MAX2424/MAX2426

when contacting these suppliers.

DESIGNATION QTY

DESCRIPTION

JU2, JU4,

JU7, JU8

Shunts

SW1

5-position dip switch

MAX2424EAI 28-pin SSOP

MAX2426EAI 28-pin SSOP

RXIN, RXOUT,

TXOUT, TXIN,

PREOUT,

EXT LO INPUT

SMA connectors (PC edge mount)

JU2, JU4, JU7,

JU8, GND,

VEXT, BPSK,

DGND

2-pin headers

LNAGAIN,

VCOADJ

1-pin headers

3) Receive image rejection can be evaluated by chang-

ing the receive input frequency to 936.4MHz (while
keeping the LO at 925.7MHz) and comparing the out-
put signal level against the one measured in step 2.

4) Before evaluating the transmitter, ensure that the

receiver is disabled by setting switch RXON to
"logic 0." Set the VCO frequency to 915MHz by
adjusting VCOADJ (R3). The transmit output power
can be evaluated by setting switch TXON to "logic
1," applying a 1MHz signal at 250mVp-p to the
TXIN port, and observing the TXOUT spectrum at
914MHz and 916MHz with a spectrum analyzer.

Adjustments and Control

VCOADJ

The VCO frequency can be tuned by adjusting on-
board potentiometer R3. It can also be tuned by first
removing the shunt from jumper JU7 and then applying
an external voltage via the VCOADJ terminal. The sup-
ply providing the external voltage must be properly
bypassed to minimize noise added to the LO.

LNAGAIN

The LNA gain can be adjusted using on-board poten-
tiometer R2. LNA gain control can also be accom-
plished by first removing the shunt from jumper JU2
and then applying an external voltage via the LNA
GAIN terminal.

RXON and TXON

The receive and transmit sections are enabled by set-
ting switches RXON and TXON to "logic 1," respectively.
Interference will result if both sections are active at the
same time. When testing either the receive or transmit
section, always disable the other section.

To disable all chip functions, set all switches to "logic 0."
To obtain an accurate reading of the device shutdown
current, remove the shunt from JU4 and move the V

connection from the VEXT terminal to the left side of JU4.

Prescaler Control

The function of PREOUT is controlled by the switches
labeled "DIV1" and "64" (Table 1).

EXT LO Input

An external LO input may be applied by making the fol-
lowing board changes: Remove R6, R7, L3, L4, C2,
C3, and C26. Add two 47pF in place of C27 and C33.
Add three 49.9

(0402) resistors in place of R6, R7,

and R21. Add three shorts in place of R11, L3, and L4.
Apply the LO signal at 0dBm to EXTLO INPUT.

Layout Considerations

The MAX2424/MAX2426 EV boards can serve as a
guide for your board layout. Take care in laying out the
oscillator tank circuit. Oscillation frequency is sensitive
to parasitic PC board capacitance, trace inductance,
and package inductance. Keep the tank layout as sym-
metrical, tightly packed, and close to the device as
possible to minimize LO feedthrough. When using a PC
board with a ground plane, a cutout in the ground
plane below the oscillator tank reduces parasitic
capacitance. Also, keep traces carrying the receive
and transmit signals as short as possible to minimize
radiation and insertion loss due to the PC board.

Evaluate: MAX2424/MAX2426

MAX2424/MAX2426 Evaluation Kits

_______________________________________________________________________________________

PREOUT

FUNCTION

SWITCH "SW1" POSITIONS

LO buffered output

Logic 1

Don't care

Prescaler, ÷64

Logic 0

Logic 1

Prescaler, ÷65

Logic 0

DIV1

Table 1. PREOUT Function Control
Switches

Evaluate: MAX2424/MAX2426

MAX2424/MAX2426 Evaluation Kits

_______________________________________________________________________________________

Figure 1. MAX2424/MAX2426 EV Kits Schematic

C28

47pF

C14
0.1

0.1

VCC

C19
47

MAX2424
MAX2426

47pF

RXIN

SMA

12nH

8.2nH

C30
0.01

C20
OPEN

L5
OPEN

R12

301

RXOUT

SMA

0.01

R18

49.9

VCC

C15
47pF

18nH

22nH

C10

47pF

TXOUT

SMA

47pF

JU6

PREOUT
SMA

C12
47pF

C31
0.01

VCC2

C32
47pF

C16

1000pF

CAP1

RXOUT

GND

RXIN

GND

TXOUT

LNAGAIN

TXIN

CAP2

GND

TANK

PREOUT

PREGND

MOD

DIV1

VCOON

RXON

TXON

C29

0.01

47pF

C25

OPEN

VCC

R13

10k

C11

0.01

OPEN

TXIN

SMA

R19

R20

49.9

R10

10k

C22

47pF

LNA

GAIN

C13

0.01

BPSK

C24

47pF

10k

VEXT

JU2

VEXT

VCC2

VCC

JU4

JU5

JU8

GND

DGND

C18

6.3V

C17
10

6.3V

C23
47pF

VCO ADJ

C1
47pF

R3
10k

VEXT

VCC2

JU7

EXTLO

INPUT

SMA

C27

OPEN

C33

OPEN

R21

OPEN

C26

C7
47pF

100nH

J13

R11

OPEN

R5
1k

R4
1k

82nH

47k

DIV1

VCOON

SW1

RXON

TXON

64/65

OFF

VEXT

10k

R14

10k

R15

10k

R16

10k

R17

10k

MAX2424

MAX2426

3.3

8.0

2.0

4.0

C2, C3

(pF)

C26
(pF)

R6, R7

(

)

6.8

3.3

Part Number MAX2424EVKIT