The SA615 is a high performance monolithic low-power mixer FM IF system incorporating a mixer/oscillator, two limiting intermediate frequency amplifiers, quadrature detector, muting, logarithmic received signal strength indicator (RSSI), and voltage regulator. The SA615 combines the functions of Signetics’ SA602 and SA604A, but features a higher mixer input intercept point, higher IF bandwidth (25MHz) and temperature compensated RSSI and limiters permitting higher performance application.

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NE615 DOUBLE BALANCED MIXER FM IF SYSTEM


What is the 615 low-power mixer FM IF system?

The SA615 is a high performance monolithic low-power mixer FM IF system incorporating a mixer/oscillator, two limiting intermediate frequency amplifiers, quadrature detector, muting, logarithmic received signal strength indicator (RSSI), and voltage regulator. The SA615 combines the functions of Signetics’ SA602 and SA604A, but features a higher mixer input intercept point, higher IF bandwidth (25MHz) and temperature compensated RSSI and limiters permitting higher performance application.

The SA605 and SA615 are functionally the same device types. The difference between the two devices lies in the guaranteed specifications. The SA615 has a higher I CC , lower input third order intercept point, lower conversion mixer gain, lower limiter gain, lower AM rejection, lower SINAD, higher THD, and higher RSSI error than the SA615.

I am particularly indebted to Philips Components and Semiconductors Australia for their most generous assistance in giving me access to material presented on this page.

Features of the 615 mixer

 Low power consumption: 5.7mA typical at 6V
 Mixer input to >500MHz
 Mixer conversion power gain of 13dB at 45MHz
 Mixer noise figure of 4.6dB at 45MHz
 XTAL oscillator effective to 150MHz (L.C. oscillator to 1GHz local oscillator can be injected)
 102dB of IF Amp/Limiter gain
 25MHz limiter small signal bandwidth
 Temperature compensated logarithmic Received Signal Strength Indicator (RSSI) with a dynamic range in excess of 90dB
 Two audio outputs – muted and unmuted
 Low external component count; suitable for crystal/ceramic/LC filters
 Excellent sensitivity: 0.22mV into 50W matching network for 12dB SINAD (Signal to Noise and Distortion ratio) for 1kHz tone with RF at 45MHz and IF at 455kHz
 SA615 meets cellular radio specifications

Applications of the 615 mixer

 Cellular radio FM IF
 High performance communications receivers
 Single conversion VHF/UHF receivers
 SCA receivers
 RF level meter
 Spectrum analyzer
 Instrumentation
 FSK and ASK data receivers
 Log amps
 Wideband low current amplification

Pin configuration of the 615 mixer

Here is the pin configuration of the 615 mixer FM IF system in figure 1 below.

This image is copyright © by Ian C. Purdie VK2TIP - 615 mixer FM IF system pin configuration

Figure 1 - 615 mixer FM IF system pin configuration

Block diagram of the 615 mixer FM IF system



This image is copyright © by Ian C. Purdie VK2TIP - block diagram of the 615 mixer FM IF system

Figure 2 - block diagram of the 615 mixer FM IF system

General considerations with using a 615 mixer FM IF system

Vcc should lie between 4.5V DC min. and 8V DC max regulated.

Input signal frequency is typically up to about 500 Mhz, while typically the oscillator will work beyond 200 Mhz.

At 45 Mhz signal input the noise figure is quoted as 5.5 dB max although typically less than that.

High performance low power mixer FM IF system

Circuit Description

The SA615 is an IF signal processing system suitable for second IF or single conversion systems with input frequency as high as 1GHz.

The bandwidth of the IF amplifier is about 40MHz, with 39.7dB(v) of gain from a 50 ohm source. The bandwidth of the limiter is about 28MHz with about 62.5dB(v) of gain from a 50 ohm source. However, the gain/bandwidth distribution is optimized for 455kHz, 1.5K source applications. The overall system is well-suited to battery operation as well as high performance and high quality products of all types.

The input stage is a Gilbert cell mixer with oscillator. Typical mixer characteristics include a noise figure of 5dB, conversion gain of 13dB, and input third-order intercept of –10dBm. The oscillator will operate in excess of 1GHz in L/C tank configurations. Hartley or Colpitts circuits can be used up to 100MHz for xtal configurations. Butler oscillators are recommended for xtal configurations up to 150MHz.

The output of the mixer is internally loaded with a 1.5K resistor permitting direct connection to a 455kHz ceramic filter. The input resistance of the limiting IF amplifiers is also 1.5K. With most 455kHz ceramic filters and many crystal filters, no impedance matching network is necessary. To achieve optimum linearity of the log signal strength indicator, there must be a 12dB(v) insertion loss between the first and second IF stages. If the IF filter or interstage network does not cause 12dB(v) insertion loss, a fixed or variable resistor can be added between the first IF output (Pin 16) and the interstage network.

The signal from the second limiting amplifier goes to a Gilbert cell quadrature detector. One port of the Gilbert cell is internally driven by the IF. The other output of the IF is AC-coupled to a tuned quadrature network. This signal, which now has a 90° phase relationship to the internal signal, drives the other port of the multiplier cell.

Overall, the IF section has a gain of 90dB. For operation at intermediate frequencies greater than 455kHz, special care must be given to layout, termination, and interstage loss to avoid instability. The demodulated output of the quadrature detector is available at two pins, one continuous and one with a mute switch. Signal attenuation with the mute activated is greater than 60dB. The mute input is very high impedance and is compatible with CMOS or TTL levels.

A log signal strength completes the circuitry. The output range is greater than 90dB and is temperature compensated.

NOTE: dB(v) = 20log V OUT /V IN

This image is copyright © by Ian C. Purdie VK2TIP - a possible configuration for the SA/NE615 mixer FM IF system

Figure 3 - a possible configuration for the SA/NE615 mixer FM IF system

Component values



This image is copyright © by Ian C. Purdie VK2TIP - component values for the possible configuration of the SA/NE615 mixer

Figure 3 - component values for the possible configuration of the SA/NE615 mixer FM IF system

You really should download the 615 mixer data sheet - (130K) which is in PDF format. This way you get all the needed information.

OBTAINING THE NE615

You might still be able to obtain the NE/SA615 from my friend Dieter (DIZ) Gentzow - W8DIZ - Loveland, Ohio U.S.A.

Pay by PayPal or check!

http://kitsandparts.com/

 

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RELATED TOPICS on 615

NE602 or NE612 Double Balanced Mixer

615 mixer data sheet - (130K) in PDF format.

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Bibliography: - Philips Semiconductors - Semiconductors for Wireless Communications 1999 - IC17

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Updated 18th February, 2002

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