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BROADBAND DC BIAS CIRCUIT FOR HIGH LINEARITY CELLULAR AMPLIFIERS

IP.com Disclosure Number: IPCOM000009850D
Original Publication Date: 2000-May-01
Included in the Prior Art Database: 2002-Sep-24
Document File: 1 page(s) / 57K

Publishing Venue

Motorola

Related People

Glenn Watanabe: AUTHOR [+3]

Abstract

A broadband DC bias circuit for high linearity cellular amplifiers is presented which has an IIP3 of +15dBm at 1.96GHz. CDMA specifications for the low noise amplifiers are very stringent with regards to the IP3. To achieve this, it is important to provide a low impedance at the difference frequency of the two-tone spacing for high llP3 and a large impedance at the high frequencies to preserve the noise figure and S parameters.

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MOTOROLA

Technical Developments

BROADBAND DC BIAS CIRCUIT FOR HIGH LINEARITY CELLULAR AMPLIFIERS

by Glenn Watanabe, Henry Lau and Tom Schiltz

ABSTRACT

A broadband DC bias circuit for high linearity cellular amplifiers is presented which has an IIP3 of +15dBm at 1.96GHz. CDMA specifications for the low noise amplifiers are very stringent with regards to the IP3. To achieve this, it is important to provide a low impedance at the difference frequency of the two-tone spacing for high llP3 and a large impedance at the high frequencies to preserve the noise figure and S parameters.

PROBLEM STATEMENT

It is very difficult to design a low noise amplifi~ er at high frequencies (i.e. 1.96GHz) that has very high linearity with low noise. We needed to achieve at IIP3 specification of +8dBm with a two-tone spacing from DC to 1.25MHz which is the two-tone spacing. One way to do this is to provide a very low resistance at low frequencies and high resistance at the RF frequencies. Currently, this is done with an RF choke (Figure. I). But, an ideal RF choke is not possible and the large inductance value resembling an ideal RF choke requires it to be placed off-chip which is not desirable. A better way to obtain the desired result is to use a feedback amplifier to provide the desired gain to lower the resistance.

RF choke/LC Trap Filter

DC Vbias LNA

. RFIn

Fig. 1 Schematic representation of an ideal RF choke used to provide DC bias and low Rout at low frequencies and high Rout at the high freq...