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SA612AD-SA612AN
Double-balanced mixer and oscillator
Philips Semiconductors
Product specification
Replaces data of September 17, 1990 1997 Nov 07
IC17 Data Handbook
Philips Semiconductors Product specification
SA612ADouble-balanced mixer and oscillator
DESCRIPTIONThe SA612A is a low-power VHF monolithic double-balanced mixer
with on-board oscillator and voltage regulator. It is intended for low
cost, low power communication systems with signal frequencies to
500MHz and local oscillator frequencies as high as 200MHz. The
mixer is a “Gilbert cell” multiplier configuration which provides gain
of 14dB or more at 45MHz.
The oscillator can be configured for a crystal, a tuned tank
operation, or as a buffer for an external L.O. Noise figure at 45MHz
is typically below 6dB and makes the device well suited for high
performance cordless phone/cellular radio. The low power
consumption makes the SA612A excellent for battery operated
equipment. Networking and other communications products can
benefit from very low radiated energy levels within systems. The
SA612A is available in an 8-lead dual in-line plastic package and an
8-lead SO (surface mounted miniature package).
FEATURES Low current consumption Low cost Operation to 500MHz Low radiated energy Low external parts count; suitable for crystal/ceramic filter Excellent sensitivity, gain, and noise figure
PIN CONFIGURATION
Figure 1. Pin Configuration
APPLICATIONS Cordless telephone Portable radio VHF transceivers RF data links Sonabuoys Communications receivers Broadband LANs HF and VHF frequency conversion Cellular radio mixer/oscillator
ORDERING INFORMATION
BLOCK DIAGRAM
Figure 2. Block Diagram
Philips Semiconductors Product specification
SA612ADouble-balanced mixer and oscillator
ABSOLUTE MAXIMUM RATINGS
AC/DC ELECTRICAL CHARACTERISTICS TA=25°C, VCC = 6V, Figure 3
DESCRIPTION OF OPERATIONThe SA612A is a Gilbert cell, an oscillator/buffer, and a temperature
compensated bias network as shown in the equivalent circuit. The
Gilbert cell is a differential amplifier (Pins 1 and 2) which drives a
balanced switching cell. The differential input stage provides gain
and determines the noise figure and signal handling performance of
the system.
The SA612A is designed for optimum low power performance.
When used with the SA614A as a 45MHz cordless phone/cellular
radio 2nd IF and demodulator, the SA612A is capable of receiving
-119dBm signals with a 12dB S/N ratio. Third-order intercept is
typically -15dBm (that’s approximately +5dBm output intercept
because of the RF gain). The system designer must be cognizant of
this large signal limitation. When designing LANs or other closed
systems where transmission levels are high, and small-signal or
signal-to-noise issues not critical, the input to the SA612A should be
appropriately scaled.
Philips Semiconductors Product specification
SA612ADouble-balanced mixer and oscillator
TEST CONFIGURATION
Figure 3. Test Configuration
Figure 4. Equivalent Circuit
Philips Semiconductors Product specification
SA612ADouble-balanced mixer and oscillator
Besides excellent low power performance well into VHF, the
SA612A is designed to be flexible. The input, output, and oscillator
ports can support a variety of configurations provided the designer
understands certain constraints, which will be explained here.
The RF inputs (Pins 1 and 2) are biased internally. They are
symmetrical. The equivalent AC input impedance is approximately
1.5k || 3pF through 50MHz. Pins 1 and 2 can be used
interchangeably, but they should not be DC biased externally. Figure
5 shows three typical input configurations.
The mixer outputs (Pins 4 and 5) are also internally biased. Each
output is connected to the internal positive supply by a 1.5kΩ
resistor. This permits direct output termination yet allows for
balanced output as well. Figure 6 shows three single-ended output
configurations and a balanced output.
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 L.O. is beyond
oscillation limits, or the system calls for an external L.O., the
external signal can be injected at Pin 6 through a DC blocking
capacitor. External L.O. should be 200mVP-P minimum to 300mVP-P
maximum.
Figure 7 shows several proven oscillator circuits. Figure 7a is
appropriate for cordless phones/cellular radio. In this circuit a third
overtone parallel-mode crystal with approximately 5pF load
capacitance should be specified. Capacitor C3 and inductor L1 act
as a fundamental trap. In fundamental mode oscillation the trap is
omitted.
Figure 8 shows a Colpitts varacter 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 circuits 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
assume correct system operation.
Figure 5. Input Configuration
Philips Semiconductors Product specification
SA612ADouble-balanced mixer and oscillator
Figure 6. Output Configuration
Figure 7. Oscillator Circuits
