_______________Detailed Description

The MAX1005 is designed to operate with the Maxim

PWT1900 (TAG-6) wireless transceiver chipset consisting

of the MAX2411 RF transceiver, the MAX2511 IF trans-

ceiver, and the MAX1007 power-control/diversity IC. The

MAX1005 integrates all the functions of an IF undersam-

pler into a single low-power integrated circuit. It is also

well suited for other time-division duplex (TDD) communi-

cations systems. This device includes a 7-bit transmit

DAC, a 5-bit receive ADC, two internal bandgap refer-

ences, clock drivers, and all necessary interface and

control logic.

Transmit DAC

generated by the MAX1005’s 7-bit DAC is used to recre-

ate the IF sub-carrier and transmission data in TDD and

other communications systems. The DAC accepts CMOS

input data in the twos-complement format and outputs a

corresponding analog voltage differentially between

AIO+ and AIO-. The full-scale output voltage range is typ-

ically ±400mV. The DAC code table is shown in Table 1.

Table 1. Transmit DAC Code Table

Receive ADC

The 5-bit receive ADC is used to directly sample or

undersample a downconverted RF signal. The ADC

converts an analog input signal to a 5-bit digital output

code in the twos-complement format. Figure 1 shows

the ADC transfer function.

Analog input signals are applied differentially between

AIO+ and AIO-, with a full-scale range of ±200mV. An

internal amplifier buffers the input signal and drives the

comparator array, minimizing loading on the external

signal source. The input amplifier has a full-power -1dB

bandwidth of at least 15MHz, making this device ideally

suited for undersampling applications.

IF Undersampler

6

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______________________________________________________________Pin Description

Two MSBs for DAC input data. D6 is the MSB.

D6, D5

9, 10

Data Input/Output Pins. If RXEN = 0 and TXEN = 1, then D4–D0 function as the five lower bits of DAC input

data, with D0 as the LSB. If RXEN = 1 and TXEN = 0, then D4–D0 function as the five data outputs for the

ADC, with D4 as the MSB and D0 as the LSB. In low-power shutdown mode (RXEN = TXEN), D0–D4 should

not be externally held high, to prevent excessive input leakage currents.

D4–D0

11–15

Clock Input. If the receive ADC is active (RXEN = 1, TXEN = 0), the analog input is sampled on the falling

edge of clock and the data outputs (D4-D0) are updated on the rising edge of CLK. If the transmit DAC is

active (TXEN = 1, RXEN = 0), input data is clocked in on the falling edge of CLK and the DAC output is

updated on the rising edge of CLK. The input clock may continue to run when the MAX1005 is shut down

(TXEN = RXEN).

CLK

16

Negative Analog Input/Output Pin. If RXEN = 1 and TXEN = 0, then AIO- is the negative analog input to the

receive ADC. If RXEN = 0 and TXEN = 1, then AIO- is the negative transmit DAC output pin.

AIO-

5

Transmit DAC Enable Input. A logic-high level on this input combined with a logic-low level on RXEN

enables the transmit DAC and disables the receive ADC. If RXEN = TXEN, the MAX1005 enters its low-

power shutdown mode.

TXEN

6

Analog Ground. Connect to analog ground plane.

AGND

7

Analog Supply Voltage, +2.7V to +5.5V

VCCA

8

Positive Analog Input/Output Pin. If RXEN = 1 and TXEN = 0, then AIO+ is the positive analog input to the

receive ADC. If RXEN = 0 and TXEN = 1, then AIO+ is the positive transmit DAC output pin.

AIO+

4

Receive ADC Enable Input. A logic-high level on this input combined with a logic-low level on TXEN enables

the receive ADC and disables the transmit DAC. If RXEN = TXEN, the MAX1005 enters its low-power shut-

down mode.

RXEN

3

PIN

Digital Ground. Connect to digital ground plane.

DGND

2

Digital Supply Voltage, +2.7V to +5.5V

VCCD

1

FUNCTION

NAME

DAC INPUT DATA

ANALOG OUTPUT

011 1111

+FS

000 0000

0

100 0000

-FS