ML2724

The RF mixer down-converts the 2.4GHz RF input signal to the first intermediate frequency (IF), where it is filtered to

remove adjacent channel signals. An active image reject mixer converts this signal down to a Low IF frequency, where

the data is limited, filtered, and demodulated. This architecture provides all the benefits of direct conversion to

baseband while maintaining the stability and robustness of a traditional super-heterodyne.

A single synthesizer is used for both the receiver and the FSK transmitter. The phase locked loop (PLL) is completely

integrated, including the voltage controlled oscillator (VCO), tuning circuits, and VCO resonator.

In RECEIVE MODE, the ML2724 is a dual conversion Low IF receiver. No external SAW filters are required. The

integrated image reject mixer gives sufficient rejection in this channel. All channel filtering and demodulation is

performed using active filters, which are automatically aligned. A matched bit rate filter and a data slicer follow the

demodulator. The sliced data is provided at the DOUT pin, and the analog data is available at AOUT.

In TRANSMIT MODE, the ML2724 generates a 2.4GHz output using the transmit mixer. An auto-aligned transmit data

filter and modulation compensation circuit results in an adjustment-free transmitter. The VCO is modulated by the

transmit data, which is put through a sigma-delta fractional-N PLL ensuring modulation accuracy. This modulation

occurs while the phase locked loop is closed, thus allowing practically infinite transmit or receive times with excellent

frequency accuracy and stability. A 3dBm FSK-modulated differential signal is output at the TXO/TXOB pins at the

2.4GHz carrier frequency.

The integrated PLL frequency synthesizer includes a fully integrated VCO, prescaler, phase detector and charge pump.

The reference frequency is generated from the incoming signal at the FREF pin, which can be either 6.144MHz or

12.288MHz. The loop filter is external to allow customers to optimize their loop bandwidth to their system’s lock time

and in-band phase noise requirements. This frequency-agile synthesizer allows the ML2724 to be used in frequency

hopped spread spectrum (FHSS) applications with nominal channel spacing of 2.048MHz. Carrier frequency is

programmed via the configuration registers and 3-wire serial interface. The VCO tank circuit (inductor and varactor) is

fully integrated.

QPO

RVVCO

220nF

150

Ω

33nF

VTUNE

Example 13KHz Loop Filter

MODES OF OPERATION

There are three key modes of operation:

STANDBY:

All circuits powered down, except the control interface (Static CMOS)

RECEIVE:

Receiver circuits active

TRANSMIT:

Modulated RF output from IC

The two operational modes are RECEIVE and TRANSMIT, controlled by RXON. XCEN is the chip enable/disable

control pin, which sets the part in operational or STANDBY modes. The relationship between the parallel control lines

and the mode of operation of the IC is given in Table 1.

XCEN

RXON

MODE

FUNCTION

0

X

STANDBY

Control interfaces active, all other circuits powered down

1

1

RECEIVE

Receiver time slot

1

0

TRANSMIT

Transmit time slot

Table 1: Modes of Operation

DS2724-F-01

FINAL DATASHEET

APRIL 2003

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