max2620euat Maxim Integrated Products, Inc., max2620euat Datasheet - Page 7

• Manufacturer Part Number: max2620euat
• Description: Max2620 10mhz To 1050mhz Integrated Rf Oscillator With Buffered Outputs
• Manufacturer: Maxim Integrated Products, Inc.

The oscillator is a common-collector, negative-
resistance type that uses the IC’s internal parasitic ele-
ments to create a negative resistance at the base-
emitter port. The transistor oscillator has been opti-
mized for low-noise operation. Base and emitter leads
are provided as external connections for a feedback
capacitor and resonator. A resonant circuit, tuned to
the appropriate frequency and connected to the base
lead, will cause oscillation. Varactor diodes may be
used in the resonant circuit to create a voltage-con-
trolled oscillator (VCO). The oscillator is internally
biased to an optimal operating point, and the base and
emitter leads need to be capacitively coupled due to
the bias voltages present.
The output buffers (OUT and OUT) are an open-
collector, differential-pair configuration and provide
load isolation to the oscillator. The outputs can be used
differentially to drive an integrated circuit mixer.
Alternatively, isolation is provided between the buffer
outputs when one output drives a mixer (either upcon-
version or downconversion) and the other output drives
a prescaler. The isolation in this configuration prevents
prescaler noise from corrupting the oscillator signal’s
spectral purity.
A logic-controlled SHDN pin turns off all bias to the IC
when pulled low.
Figure 1. 900MHz Test Circuit
_______________Detailed Description
TEST PORT
V
CC
ON
1000pF
_______________________________________________________________________________________
C2*
OFF
1000pF
V
CC
10
10
C3*
2.7pF
C4*
1pF
RF Oscillator with Buffered Outputs
1000pF
1
2
3
4
Output Buffers
TANK
FDBK
SHDN
V
CC
1
SUPPLY
10MHz to 1050MHz Integrated
Oscillator
BIAS
MAX2620
At the frequency of interest, the MAX2620 portion of
Figure 2 shows the one-port circuit model for the TANK
pin (test port in Figure 1).
For the circuit to oscillate at a desired frequency, the res-
onant tank circuit connected to TANK must present an
impedance that is a complement to the network
(Figure 2). This resonant tank circuit must have a positive
real component that is a maximum of one-half the magni-
tude of the negative real part of the oscillator device, as
well as a reactive component that is opposite in sign to
the reactive component of the oscillator device.
Figure 2. Simplified Oscillator Circuit Model
__________Applications Information
1000pF
LESS THAN 1/2
V
GND
OUT
OUT
CC
TIMES R
2
220nH
L3*
8
7
6
5
L
V
CC
1000pF
51
RESONANT
TANK
V
1000pF
jX
CC
VCC
L
1000pF
1000pF
C13*
C10*
*AT 10MHz, CHANGE TO:
C3 = C4 = 270pF
L3 = 10 H
C2 = C10 = C13 = 0.01 F
TANK
Design Principles
OUT
OUT
OSCILLATOR
DEVICE
Z
Z
O
O
-jX
= 50
= 50
T
-R
n
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