CMX017D6 데이터 시트보기 (PDF) - MX-COM Inc

부품명

상세내역

제조사

CMX017D6

UHF FM/FSK Transmitter

MX-COM Inc  

UHF FM/FSK Transmitter

6

CMX017 Advance Information

4 General Description

The CMX017 is a single chip UHF FM/FSK transmitter that combines both the RF VCO Modulator and RF

Power Amplifier. It is suitable for both audio FM and digital FSK transmissions.

A buffered oscillator output provides the RF signal drive to an external synthesizer or fixed frequency phase-

locked loop for channel frequency selection. Modulator output power is adjustable over a 20dB range and the

integrated power amplifier delivers up to +20dBm. The device also includes a powersave mode: “Transmit

Standby” and a zero-power mode: “Sleep”. These allow independent power down control of both the

modulator and power amplifier, thereby maximizing battery life. The device can be used in conjunction with

the CMX018 a double-conversion super-heterodyne receiver, to implement a complete UHF radio link.

4.1 FM/FSK Modulator + PA Driver

The modulator circuit uses an integrated oscillator whose frequency can be directly modulated by the DC-

coupled input base-band signal, at the MODIN pin, to generate a frequency modulated (FM or FSK) RF

signal. The oscillator requires an external varactor and resonator circuit, connected at the TANK pin, to tune

to the required RF channel. A buffered oscillator signal is provided from an open-collector output, at the

OSCOUT pin, to drive an external frequency synthesizer for the channel selection.

The output power, at the MODOUT pin, is variable over a 20dB range. The output power is maximum when

the GAIN pin is connected to VCC and is reduced by typically 20dB when this pin is connected to 0V. The

output impedance at the MODOUT pin is typically 50Ω.

4.2 Power Amplifier (PA)

The power amplifier has two internal stages, each biased for class-B operation, and is designed to have a

fixed overall power gain. The input and output impedances can be terminated with 50Ω. A typical power gain

improvement of 2dB is achieved using simple external matching networks.

4.3 Powersave and Zero-Power Modes

The Modulator and Buffered Oscillator stages are powered down independently of the PA Driver + Power

Amplifier stages by means of the ENLMOD and ENLPA logic inputs:

A logic ‘0’ at ENLMOD powers down the Modulator and Buffered Oscillator stages.

A logic ‘0’ at ENLPA powers down the PA Driver and Power Amplifier stages.

Refer to the block diagram in Figure 1 and to Section 5.

5 Application Notes

5.1 Generation of the Modulated RF Signal

The modulator on the CMX017 relies on the direct modulation of the RF Voltage Controlled Oscillator (VCO),

which is stabilized to the channel center frequency by an external Frequency Synthesizer or Phase Locked

Loop (PLL). The user has control over the external PLL filter and VCO tank components and choice of these

components will have an impact upon the following PLL parameters:-

Closed loop bandwidth, settling time and transient response

Modulation linearity

VCO phase noise

Three modulation requirements may be achieved as follows:

5.1.1 The minimum modulation signal frequency is above the PLL Closed Loop Bandwidth

In applications where the transmit channel frequency is fixed or occasionally changed, a narrow PLL

bandwidth can be chosen such that the minimum modulation frequency is in excess of the PLL bandwidth.

With the PLL active whilst the base-band signal is applied to the modulator there will be negligible distortion of

the modulated RF output signal. A benefit of this technique is that an output phase noise improvement is

achieved, compared to the free running VCO phase noise characteristic.

5.1.2 The minimum modulation signal frequency is within the PLL Closed Loop Bandwidth

In Frequency Hopped Spread Spectrum applications the frequency synthesizer must be agile. Consequently

the PLL bandwidth should be designed to achieve the required hop-rate and, in most systems this bandwidth

will exceed the minimum modulation frequency. With the PLL active during modulation, the loop will

©1999 MX-COM, Inc.

www.mxcom.com Tel: 800 638 5577 336 744 5050 Fax: 336 744 5054

Doc. # 20480193.003

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA

All trademarks and service marks are held by their respective companies

Share Link: