Ultra Low Current Low Noise Wide Band VCO Design Based On RSSI Tracking Algorithm and RF Level Shifter
Original Publication Date: 2004-Mar-03
Included in the Prior Art Database: 2004-Mar-03
Nir Corse: AUTHOR [+3]
AbstractA Circuit for reducing Voltage Controlled Oscillator (VCO) current consumption using a RSSI tracking algorithm.
Based On RSSI Tracking Algorithm and RF Level Shifter
Nir Corse, Ronen Klaiman, Haim Malka
A Circuit for reducing Voltage Controlled Oscillator (VCO) current consumption using a RSSI tracking algorithm.
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:
TETRA Receiver blocking
Rx interference @ 50 - 100 KHz = -40 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...