SA602A Datasheet, PDF (4/11 Pages) NXP Semiconductors – Double-balanced mixer and oscillator

Philips Semiconductors
Double-balanced mixer and oscillator
Product specification
SA602A
The oscillator is capable of sustaining oscillation beyond 200MHz in
crystal or tuned tank configurations. The upper limit of operation is
determined by tank “Q” and required drive levels. The higher the
“Q” of the tank or the smaller the required drive, the higher the
permissible oscillation frequency. If the required LO is beyond
oscillation limits, or the system calls for an external LO, the external
signal can be injected at Pin 6 through a DC blocking capacitor.
External LO should be at least 200mV_P-P.
Figure 7 shows several proven oscillator circuits. Figure 7a is
appropriate for cellular radio. As shown, an overtone mode of
operation is utilized. Capacitor C3 and inductor L1 suppress
oscillation at the crystal fundamental frequency. In the fundamental
mode, the suppression network is omitted.
Figure 8 shows a Colpitts varactor tuned tank oscillator suitable for
synthesizer-controlled applications. It is important to buffer the
output of this circuit to assure that switching spikes from the first
counter or prescaler do not end up in the oscillator spectrum. The
dual-gate MOSFET provides optimum isolation with low current.
The FET offers good isolation, simplicity, and low current, while the
bipolar transistors provide the simple solution for non-critical
applications. The resistive divider in the emitter-follower circuit
should be chosen to provide the minimum input signal which will
assure correct system operation.
When operated above 100MHz, the oscillator may not start if the Q
of the tank is too low. A 22kΩ resistor from Pin 7 to ground will
increase the DC bias current of the oscillator transistor. This
improves the AC operating characteristic of the transistor and
should help the oscillator to start. A 22kΩ resistor will not upset the
other DC biasing internal to the device, but smaller resistance
values should be avoided.
V_CC
6.8µF
5.5µH
100nF
0.5 to 1.3µH
1nF
22pF
10pF
34.545MHz THIRD OVERTONE CRYSTAL
10nF
8
7
6
5
602A
1.5 to
44.2µH
150pF
OUTPUT
330pF
INPUT
47pF
220pF
1
2
3
4
0.209 to 0.283µH
100nF
Figure 3. Test Configuration
120pF
SR00070
1997 Nov 07
4