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Ultra Low Current Low Noise Wide Band VCO Design Based On RSSI Tracking Algorithm and RF Level Shifter

IP.com Disclosure Number: IPCOM000022257D
Original Publication Date: 2004-Mar-03
Included in the Prior Art Database: 2004-Mar-03
Document File: 3 page(s) / 32K

Publishing Venue

Motorola

Related People

Nir Corse: AUTHOR [+3]

Abstract

A Circuit for reducing Voltage Controlled Oscillator (VCO) current consumption using a RSSI tracking algorithm.

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Ultra Low Current Low Noise Wide Band VCO Design

Based On RSSI Tracking Algorithm and RF Level Shifter

Nir Corse, Ronen Klaiman, Haim Malka

Abstract

A Circuit for reducing Voltage Controlled Oscillator (VCO) current consumption using a RSSI tracking algorithm.

Description

The following article presents a new method for reducing Voltage Controlled Oscillator (VCO) current consumption using RSSI tracking algorithm and simple low cost RF level shifter. In direct conversion systems the main VCO serves as a single local oscillator in the RX section. The VCO current is set by the need to provide sufficient phase noise performance, RF level and oscillator loop gain for start up. A 760 MHz – 860 MHz, 2.4 V, 5.2 MA GMT VCO was designed. Minimum –122 dBc / Hz @ 50 KHz was measured over the frequency band.

The VCO will present –115.5 dBc / Hz @ 50 KHz for 2.4 MA. In our system the typical in band noise is limited to ~ -127 dBc/Hz causing the synthesizer phase noise performance to be limited by the VCO performance. The synthesizer is followed by a divide by 2 improving the over all phase noise by ~ 6 dB. The over all system performance is ~ -121.5 dBc/Hz @ 50 KHz for 2.4 MA. When the VCO is set to 5.2 MA the over all estimated performance is ~ -127.5 dBc/Hz.

In TETRA systems the phase noise performance is set by the need to provide sufficient receiver blocking and adjacent channel performance. The blocking is calculated as follows:

 
 

Desired Channel

 
 

TETRA Receiver blocking

 
 

Noise

 
 

Rx interference @ 50 - 100 KHz = -40 dBm

Distortion

 
@ 100 - 200 KHz = -35 dBm

@ 200 - 500 KHz = -30 dBm

@ > 500 KHz = -25 dBm

Desired Channel [dBm] – (Noise [dBm/BW] + Distortion [dBm]) = C/N [dB]

Desired Channel = -109 dBm (In order to establish the sensitivity requirements).

At worst case Noise = Distortion

C / N at TETRA = 8.25 dB

-109 [dBm] – (3 dB + Distortion [dBm]) = 8.25 dB

Max. Distortion [dBm] = -120.25 dBm

The distortion at the antenna is at 50 kHz offset and –40 dBm power level. In order to achieve –120.25 dBm, we need minimum signal attenuation of 80.25 dB...